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   1<?xml version="1.0" encoding="UTF-8"?>
   2<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN"
   3        "http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" []>
   4
   5<book id="libataDevGuide">
   6 <bookinfo>
   7  <title>libATA Developer's Guide</title>
   8  
   9  <authorgroup>
  10   <author>
  11    <firstname>Jeff</firstname>
  12    <surname>Garzik</surname>
  13   </author>
  14  </authorgroup>
  15
  16  <copyright>
  17   <year>2003-2006</year>
  18   <holder>Jeff Garzik</holder>
  19  </copyright>
  20
  21  <legalnotice>
  22   <para>
  23   The contents of this file are subject to the Open
  24   Software License version 1.1 that can be found at
  25   <ulink url="http://fedoraproject.org/wiki/Licensing:OSL1.1">http://fedoraproject.org/wiki/Licensing:OSL1.1</ulink>
  26   and is included herein by reference.
  27   </para>
  28
  29   <para>
  30   Alternatively, the contents of this file may be used under the terms
  31   of the GNU General Public License version 2 (the "GPL") as distributed
  32   in the kernel source COPYING file, in which case the provisions of
  33   the GPL are applicable instead of the above.  If you wish to allow
  34   the use of your version of this file only under the terms of the
  35   GPL and not to allow others to use your version of this file under
  36   the OSL, indicate your decision by deleting the provisions above and
  37   replace them with the notice and other provisions required by the GPL.
  38   If you do not delete the provisions above, a recipient may use your
  39   version of this file under either the OSL or the GPL.
  40   </para>
  41
  42  </legalnotice>
  43 </bookinfo>
  44
  45<toc></toc>
  46
  47  <chapter id="libataIntroduction">
  48     <title>Introduction</title>
  49  <para>
  50  libATA is a library used inside the Linux kernel to support ATA host
  51  controllers and devices.  libATA provides an ATA driver API, class
  52  transports for ATA and ATAPI devices, and SCSI&lt;-&gt;ATA translation
  53  for ATA devices according to the T10 SAT specification.
  54  </para>
  55  <para>
  56  This Guide documents the libATA driver API, library functions, library
  57  internals, and a couple sample ATA low-level drivers.
  58  </para>
  59  </chapter>
  60
  61  <chapter id="libataDriverApi">
  62     <title>libata Driver API</title>
  63     <para>
  64     struct ata_port_operations is defined for every low-level libata
  65     hardware driver, and it controls how the low-level driver
  66     interfaces with the ATA and SCSI layers.
  67     </para>
  68     <para>
  69     FIS-based drivers will hook into the system with ->qc_prep() and
  70     ->qc_issue() high-level hooks.  Hardware which behaves in a manner
  71     similar to PCI IDE hardware may utilize several generic helpers,
  72     defining at a bare minimum the bus I/O addresses of the ATA shadow
  73     register blocks.
  74     </para>
  75     <sect1>
  76        <title>struct ata_port_operations</title>
  77
  78        <sect2><title>Disable ATA port</title>
  79        <programlisting>
  80void (*port_disable) (struct ata_port *);
  81        </programlisting>
  82
  83        <para>
  84        Called from ata_bus_probe() error path, as well as when
  85        unregistering from the SCSI module (rmmod, hot unplug).
  86        This function should do whatever needs to be done to take the
  87        port out of use.  In most cases, ata_port_disable() can be used
  88        as this hook.
  89        </para>
  90        <para>
  91        Called from ata_bus_probe() on a failed probe.
  92        Called from ata_scsi_release().
  93        </para>
  94
  95        </sect2>
  96
  97        <sect2><title>Post-IDENTIFY device configuration</title>
  98        <programlisting>
  99void (*dev_config) (struct ata_port *, struct ata_device *);
 100        </programlisting>
 101
 102        <para>
 103        Called after IDENTIFY [PACKET] DEVICE is issued to each device
 104        found.  Typically used to apply device-specific fixups prior to
 105        issue of SET FEATURES - XFER MODE, and prior to operation.
 106        </para>
 107        <para>
 108        This entry may be specified as NULL in ata_port_operations.
 109        </para>
 110
 111        </sect2>
 112
 113        <sect2><title>Set PIO/DMA mode</title>
 114        <programlisting>
 115void (*set_piomode) (struct ata_port *, struct ata_device *);
 116void (*set_dmamode) (struct ata_port *, struct ata_device *);
 117void (*post_set_mode) (struct ata_port *);
 118unsigned int (*mode_filter) (struct ata_port *, struct ata_device *, unsigned int);
 119        </programlisting>
 120
 121        <para>
 122        Hooks called prior to the issue of SET FEATURES - XFER MODE
 123        command.  The optional ->mode_filter() hook is called when libata
 124        has built a mask of the possible modes. This is passed to the 
 125        ->mode_filter() function which should return a mask of valid modes
 126        after filtering those unsuitable due to hardware limits. It is not
 127        valid to use this interface to add modes.
 128        </para>
 129        <para>
 130        dev->pio_mode and dev->dma_mode are guaranteed to be valid when
 131        ->set_piomode() and when ->set_dmamode() is called. The timings for
 132        any other drive sharing the cable will also be valid at this point.
 133        That is the library records the decisions for the modes of each
 134        drive on a channel before it attempts to set any of them.
 135        </para>
 136        <para>
 137        ->post_set_mode() is
 138        called unconditionally, after the SET FEATURES - XFER MODE
 139        command completes successfully.
 140        </para>
 141
 142        <para>
 143        ->set_piomode() is always called (if present), but
 144        ->set_dma_mode() is only called if DMA is possible.
 145        </para>
 146
 147        </sect2>
 148
 149        <sect2><title>Taskfile read/write</title>
 150        <programlisting>
 151void (*sff_tf_load) (struct ata_port *ap, struct ata_taskfile *tf);
 152void (*sff_tf_read) (struct ata_port *ap, struct ata_taskfile *tf);
 153        </programlisting>
 154
 155        <para>
 156        ->tf_load() is called to load the given taskfile into hardware
 157        registers / DMA buffers.  ->tf_read() is called to read the
 158        hardware registers / DMA buffers, to obtain the current set of
 159        taskfile register values.
 160        Most drivers for taskfile-based hardware (PIO or MMIO) use
 161        ata_sff_tf_load() and ata_sff_tf_read() for these hooks.
 162        </para>
 163
 164        </sect2>
 165
 166        <sect2><title>PIO data read/write</title>
 167        <programlisting>
 168void (*sff_data_xfer) (struct ata_device *, unsigned char *, unsigned int, int);
 169        </programlisting>
 170
 171        <para>
 172All bmdma-style drivers must implement this hook.  This is the low-level
 173operation that actually copies the data bytes during a PIO data
 174transfer.
 175Typically the driver will choose one of ata_sff_data_xfer_noirq(),
 176ata_sff_data_xfer(), or ata_sff_data_xfer32().
 177        </para>
 178
 179        </sect2>
 180
 181        <sect2><title>ATA command execute</title>
 182        <programlisting>
 183void (*sff_exec_command)(struct ata_port *ap, struct ata_taskfile *tf);
 184        </programlisting>
 185
 186        <para>
 187        causes an ATA command, previously loaded with
 188        ->tf_load(), to be initiated in hardware.
 189        Most drivers for taskfile-based hardware use ata_sff_exec_command()
 190        for this hook.
 191        </para>
 192
 193        </sect2>
 194
 195        <sect2><title>Per-cmd ATAPI DMA capabilities filter</title>
 196        <programlisting>
 197int (*check_atapi_dma) (struct ata_queued_cmd *qc);
 198        </programlisting>
 199
 200        <para>
 201Allow low-level driver to filter ATA PACKET commands, returning a status
 202indicating whether or not it is OK to use DMA for the supplied PACKET
 203command.
 204        </para>
 205        <para>
 206        This hook may be specified as NULL, in which case libata will
 207        assume that atapi dma can be supported.
 208        </para>
 209
 210        </sect2>
 211
 212        <sect2><title>Read specific ATA shadow registers</title>
 213        <programlisting>
 214u8   (*sff_check_status)(struct ata_port *ap);
 215u8   (*sff_check_altstatus)(struct ata_port *ap);
 216        </programlisting>
 217
 218        <para>
 219        Reads the Status/AltStatus ATA shadow register from
 220        hardware.  On some hardware, reading the Status register has
 221        the side effect of clearing the interrupt condition.
 222        Most drivers for taskfile-based hardware use
 223        ata_sff_check_status() for this hook.
 224        </para>
 225
 226        </sect2>
 227
 228        <sect2><title>Write specific ATA shadow register</title>
 229        <programlisting>
 230void (*sff_set_devctl)(struct ata_port *ap, u8 ctl);
 231        </programlisting>
 232
 233        <para>
 234        Write the device control ATA shadow register to the hardware.
 235        Most drivers don't need to define this.
 236        </para>
 237
 238        </sect2>
 239
 240        <sect2><title>Select ATA device on bus</title>
 241        <programlisting>
 242void (*sff_dev_select)(struct ata_port *ap, unsigned int device);
 243        </programlisting>
 244
 245        <para>
 246        Issues the low-level hardware command(s) that causes one of N
 247        hardware devices to be considered 'selected' (active and
 248        available for use) on the ATA bus.  This generally has no
 249        meaning on FIS-based devices.
 250        </para>
 251        <para>
 252        Most drivers for taskfile-based hardware use
 253        ata_sff_dev_select() for this hook.
 254        </para>
 255
 256        </sect2>
 257
 258        <sect2><title>Private tuning method</title>
 259        <programlisting>
 260void (*set_mode) (struct ata_port *ap);
 261        </programlisting>
 262
 263        <para>
 264        By default libata performs drive and controller tuning in
 265        accordance with the ATA timing rules and also applies blacklists
 266        and cable limits. Some controllers need special handling and have
 267        custom tuning rules, typically raid controllers that use ATA
 268        commands but do not actually do drive timing.
 269        </para>
 270
 271        <warning>
 272        <para>
 273        This hook should not be used to replace the standard controller
 274        tuning logic when a controller has quirks. Replacing the default
 275        tuning logic in that case would bypass handling for drive and
 276        bridge quirks that may be important to data reliability. If a
 277        controller needs to filter the mode selection it should use the
 278        mode_filter hook instead.
 279        </para>
 280        </warning>
 281
 282        </sect2>
 283
 284        <sect2><title>Control PCI IDE BMDMA engine</title>
 285        <programlisting>
 286void (*bmdma_setup) (struct ata_queued_cmd *qc);
 287void (*bmdma_start) (struct ata_queued_cmd *qc);
 288void (*bmdma_stop) (struct ata_port *ap);
 289u8   (*bmdma_status) (struct ata_port *ap);
 290        </programlisting>
 291
 292        <para>
 293When setting up an IDE BMDMA transaction, these hooks arm
 294(->bmdma_setup), fire (->bmdma_start), and halt (->bmdma_stop)
 295the hardware's DMA engine.  ->bmdma_status is used to read the standard
 296PCI IDE DMA Status register.
 297        </para>
 298
 299        <para>
 300These hooks are typically either no-ops, or simply not implemented, in
 301FIS-based drivers.
 302        </para>
 303        <para>
 304Most legacy IDE drivers use ata_bmdma_setup() for the bmdma_setup()
 305hook.  ata_bmdma_setup() will write the pointer to the PRD table to
 306the IDE PRD Table Address register, enable DMA in the DMA Command
 307register, and call exec_command() to begin the transfer.
 308        </para>
 309        <para>
 310Most legacy IDE drivers use ata_bmdma_start() for the bmdma_start()
 311hook.  ata_bmdma_start() will write the ATA_DMA_START flag to the DMA
 312Command register.
 313        </para>
 314        <para>
 315Many legacy IDE drivers use ata_bmdma_stop() for the bmdma_stop()
 316hook.  ata_bmdma_stop() clears the ATA_DMA_START flag in the DMA
 317command register.
 318        </para>
 319        <para>
 320Many legacy IDE drivers use ata_bmdma_status() as the bmdma_status() hook.
 321        </para>
 322
 323        </sect2>
 324
 325        <sect2><title>High-level taskfile hooks</title>
 326        <programlisting>
 327void (*qc_prep) (struct ata_queued_cmd *qc);
 328int (*qc_issue) (struct ata_queued_cmd *qc);
 329        </programlisting>
 330
 331        <para>
 332        Higher-level hooks, these two hooks can potentially supercede
 333        several of the above taskfile/DMA engine hooks.  ->qc_prep is
 334        called after the buffers have been DMA-mapped, and is typically
 335        used to populate the hardware's DMA scatter-gather table.
 336        Most drivers use the standard ata_qc_prep() helper function, but
 337        more advanced drivers roll their own.
 338        </para>
 339        <para>
 340        ->qc_issue is used to make a command active, once the hardware
 341        and S/G tables have been prepared.  IDE BMDMA drivers use the
 342        helper function ata_qc_issue_prot() for taskfile protocol-based
 343        dispatch.  More advanced drivers implement their own ->qc_issue.
 344        </para>
 345        <para>
 346        ata_qc_issue_prot() calls ->tf_load(), ->bmdma_setup(), and
 347        ->bmdma_start() as necessary to initiate a transfer.
 348        </para>
 349
 350        </sect2>
 351
 352        <sect2><title>Exception and probe handling (EH)</title>
 353        <programlisting>
 354void (*eng_timeout) (struct ata_port *ap);
 355void (*phy_reset) (struct ata_port *ap);
 356        </programlisting>
 357
 358        <para>
 359Deprecated.  Use ->error_handler() instead.
 360        </para>
 361
 362        <programlisting>
 363void (*freeze) (struct ata_port *ap);
 364void (*thaw) (struct ata_port *ap);
 365        </programlisting>
 366
 367        <para>
 368ata_port_freeze() is called when HSM violations or some other
 369condition disrupts normal operation of the port.  A frozen port
 370is not allowed to perform any operation until the port is
 371thawed, which usually follows a successful reset.
 372        </para>
 373
 374        <para>
 375The optional ->freeze() callback can be used for freezing the port
 376hardware-wise (e.g. mask interrupt and stop DMA engine).  If a
 377port cannot be frozen hardware-wise, the interrupt handler
 378must ack and clear interrupts unconditionally while the port
 379is frozen.
 380        </para>
 381        <para>
 382The optional ->thaw() callback is called to perform the opposite of ->freeze():
 383prepare the port for normal operation once again.  Unmask interrupts,
 384start DMA engine, etc.
 385        </para>
 386
 387        <programlisting>
 388void (*error_handler) (struct ata_port *ap);
 389        </programlisting>
 390
 391        <para>
 392->error_handler() is a driver's hook into probe, hotplug, and recovery
 393and other exceptional conditions.  The primary responsibility of an
 394implementation is to call ata_do_eh() or ata_bmdma_drive_eh() with a set
 395of EH hooks as arguments:
 396        </para>
 397
 398        <para>
 399'prereset' hook (may be NULL) is called during an EH reset, before any other actions
 400are taken.
 401        </para>
 402
 403        <para>
 404'postreset' hook (may be NULL) is called after the EH reset is performed.  Based on
 405existing conditions, severity of the problem, and hardware capabilities,
 406        </para>
 407
 408        <para>
 409Either 'softreset' (may be NULL) or 'hardreset' (may be NULL) will be
 410called to perform the low-level EH reset.
 411        </para>
 412
 413        <programlisting>
 414void (*post_internal_cmd) (struct ata_queued_cmd *qc);
 415        </programlisting>
 416
 417        <para>
 418Perform any hardware-specific actions necessary to finish processing
 419after executing a probe-time or EH-time command via ata_exec_internal().
 420        </para>
 421
 422        </sect2>
 423
 424        <sect2><title>Hardware interrupt handling</title>
 425        <programlisting>
 426irqreturn_t (*irq_handler)(int, void *, struct pt_regs *);
 427void (*irq_clear) (struct ata_port *);
 428        </programlisting>
 429
 430        <para>
 431        ->irq_handler is the interrupt handling routine registered with
 432        the system, by libata.  ->irq_clear is called during probe just
 433        before the interrupt handler is registered, to be sure hardware
 434        is quiet.
 435        </para>
 436        <para>
 437        The second argument, dev_instance, should be cast to a pointer
 438        to struct ata_host_set.
 439        </para>
 440        <para>
 441        Most legacy IDE drivers use ata_sff_interrupt() for the
 442        irq_handler hook, which scans all ports in the host_set,
 443        determines which queued command was active (if any), and calls
 444        ata_sff_host_intr(ap,qc).
 445        </para>
 446        <para>
 447        Most legacy IDE drivers use ata_sff_irq_clear() for the
 448        irq_clear() hook, which simply clears the interrupt and error
 449        flags in the DMA status register.
 450        </para>
 451
 452        </sect2>
 453
 454        <sect2><title>SATA phy read/write</title>
 455        <programlisting>
 456int (*scr_read) (struct ata_port *ap, unsigned int sc_reg,
 457                 u32 *val);
 458int (*scr_write) (struct ata_port *ap, unsigned int sc_reg,
 459                   u32 val);
 460        </programlisting>
 461
 462        <para>
 463        Read and write standard SATA phy registers.  Currently only used
 464        if ->phy_reset hook called the sata_phy_reset() helper function.
 465        sc_reg is one of SCR_STATUS, SCR_CONTROL, SCR_ERROR, or SCR_ACTIVE.
 466        </para>
 467
 468        </sect2>
 469
 470        <sect2><title>Init and shutdown</title>
 471        <programlisting>
 472int (*port_start) (struct ata_port *ap);
 473void (*port_stop) (struct ata_port *ap);
 474void (*host_stop) (struct ata_host_set *host_set);
 475        </programlisting>
 476
 477        <para>
 478        ->port_start() is called just after the data structures for each
 479        port are initialized.  Typically this is used to alloc per-port
 480        DMA buffers / tables / rings, enable DMA engines, and similar
 481        tasks.  Some drivers also use this entry point as a chance to
 482        allocate driver-private memory for ap->private_data.
 483        </para>
 484        <para>
 485        Many drivers use ata_port_start() as this hook or call
 486        it from their own port_start() hooks.  ata_port_start()
 487        allocates space for a legacy IDE PRD table and returns.
 488        </para>
 489        <para>
 490        ->port_stop() is called after ->host_stop().  Its sole function
 491        is to release DMA/memory resources, now that they are no longer
 492        actively being used.  Many drivers also free driver-private
 493        data from port at this time.
 494        </para>
 495        <para>
 496        ->host_stop() is called after all ->port_stop() calls
 497have completed.  The hook must finalize hardware shutdown, release DMA
 498and other resources, etc.
 499        This hook may be specified as NULL, in which case it is not called.
 500        </para>
 501
 502        </sect2>
 503
 504     </sect1>
 505  </chapter>
 506
 507  <chapter id="libataEH">
 508        <title>Error handling</title>
 509
 510        <para>
 511        This chapter describes how errors are handled under libata.
 512        Readers are advised to read SCSI EH
 513        (Documentation/scsi/scsi_eh.txt) and ATA exceptions doc first.
 514        </para>
 515
 516        <sect1><title>Origins of commands</title>
 517        <para>
 518        In libata, a command is represented with struct ata_queued_cmd
 519        or qc.  qc's are preallocated during port initialization and
 520        repetitively used for command executions.  Currently only one
 521        qc is allocated per port but yet-to-be-merged NCQ branch
 522        allocates one for each tag and maps each qc to NCQ tag 1-to-1.
 523        </para>
 524        <para>
 525        libata commands can originate from two sources - libata itself
 526        and SCSI midlayer.  libata internal commands are used for
 527        initialization and error handling.  All normal blk requests
 528        and commands for SCSI emulation are passed as SCSI commands
 529        through queuecommand callback of SCSI host template.
 530        </para>
 531        </sect1>
 532
 533        <sect1><title>How commands are issued</title>
 534
 535        <variablelist>
 536
 537        <varlistentry><term>Internal commands</term>
 538        <listitem>
 539        <para>
 540        First, qc is allocated and initialized using
 541        ata_qc_new_init().  Although ata_qc_new_init() doesn't
 542        implement any wait or retry mechanism when qc is not
 543        available, internal commands are currently issued only during
 544        initialization and error recovery, so no other command is
 545        active and allocation is guaranteed to succeed.
 546        </para>
 547        <para>
 548        Once allocated qc's taskfile is initialized for the command to
 549        be executed.  qc currently has two mechanisms to notify
 550        completion.  One is via qc->complete_fn() callback and the
 551        other is completion qc->waiting.  qc->complete_fn() callback
 552        is the asynchronous path used by normal SCSI translated
 553        commands and qc->waiting is the synchronous (issuer sleeps in
 554        process context) path used by internal commands.
 555        </para>
 556        <para>
 557        Once initialization is complete, host_set lock is acquired
 558        and the qc is issued.
 559        </para>
 560        </listitem>
 561        </varlistentry>
 562
 563        <varlistentry><term>SCSI commands</term>
 564        <listitem>
 565        <para>
 566        All libata drivers use ata_scsi_queuecmd() as
 567        hostt->queuecommand callback.  scmds can either be simulated
 568        or translated.  No qc is involved in processing a simulated
 569        scmd.  The result is computed right away and the scmd is
 570        completed.
 571        </para>
 572        <para>
 573        For a translated scmd, ata_qc_new_init() is invoked to
 574        allocate a qc and the scmd is translated into the qc.  SCSI
 575        midlayer's completion notification function pointer is stored
 576        into qc->scsidone.
 577        </para>
 578        <para>
 579        qc->complete_fn() callback is used for completion
 580        notification.  ATA commands use ata_scsi_qc_complete() while
 581        ATAPI commands use atapi_qc_complete().  Both functions end up
 582        calling qc->scsidone to notify upper layer when the qc is
 583        finished.  After translation is completed, the qc is issued
 584        with ata_qc_issue().
 585        </para>
 586        <para>
 587        Note that SCSI midlayer invokes hostt->queuecommand while
 588        holding host_set lock, so all above occur while holding
 589        host_set lock.
 590        </para>
 591        </listitem>
 592        </varlistentry>
 593
 594        </variablelist>
 595        </sect1>
 596
 597        <sect1><title>How commands are processed</title>
 598        <para>
 599        Depending on which protocol and which controller are used,
 600        commands are processed differently.  For the purpose of
 601        discussion, a controller which uses taskfile interface and all
 602        standard callbacks is assumed.
 603        </para>
 604        <para>
 605        Currently 6 ATA command protocols are used.  They can be
 606        sorted into the following four categories according to how
 607        they are processed.
 608        </para>
 609
 610        <variablelist>
 611           <varlistentry><term>ATA NO DATA or DMA</term>
 612           <listitem>
 613           <para>
 614           ATA_PROT_NODATA and ATA_PROT_DMA fall into this category.
 615           These types of commands don't require any software
 616           intervention once issued.  Device will raise interrupt on
 617           completion.
 618           </para>
 619           </listitem>
 620           </varlistentry>
 621
 622           <varlistentry><term>ATA PIO</term>
 623           <listitem>
 624           <para>
 625           ATA_PROT_PIO is in this category.  libata currently
 626           implements PIO with polling.  ATA_NIEN bit is set to turn
 627           off interrupt and pio_task on ata_wq performs polling and
 628           IO.
 629           </para>
 630           </listitem>
 631           </varlistentry>
 632
 633           <varlistentry><term>ATAPI NODATA or DMA</term>
 634           <listitem>
 635           <para>
 636           ATA_PROT_ATAPI_NODATA and ATA_PROT_ATAPI_DMA are in this
 637           category.  packet_task is used to poll BSY bit after
 638           issuing PACKET command.  Once BSY is turned off by the
 639           device, packet_task transfers CDB and hands off processing
 640           to interrupt handler.
 641           </para>
 642           </listitem>
 643           </varlistentry>
 644
 645           <varlistentry><term>ATAPI PIO</term>
 646           <listitem>
 647           <para>
 648           ATA_PROT_ATAPI is in this category.  ATA_NIEN bit is set
 649           and, as in ATAPI NODATA or DMA, packet_task submits cdb.
 650           However, after submitting cdb, further processing (data
 651           transfer) is handed off to pio_task.
 652           </para>
 653           </listitem>
 654           </varlistentry>
 655        </variablelist>
 656        </sect1>
 657
 658        <sect1><title>How commands are completed</title>
 659        <para>
 660        Once issued, all qc's are either completed with
 661        ata_qc_complete() or time out.  For commands which are handled
 662        by interrupts, ata_host_intr() invokes ata_qc_complete(), and,
 663        for PIO tasks, pio_task invokes ata_qc_complete().  In error
 664        cases, packet_task may also complete commands.
 665        </para>
 666        <para>
 667        ata_qc_complete() does the following.
 668        </para>
 669
 670        <orderedlist>
 671
 672        <listitem>
 673        <para>
 674        DMA memory is unmapped.
 675        </para>
 676        </listitem>
 677
 678        <listitem>
 679        <para>
 680        ATA_QCFLAG_ACTIVE is clared from qc->flags.
 681        </para>
 682        </listitem>
 683
 684        <listitem>
 685        <para>
 686        qc->complete_fn() callback is invoked.  If the return value of
 687        the callback is not zero.  Completion is short circuited and
 688        ata_qc_complete() returns.
 689        </para>
 690        </listitem>
 691
 692        <listitem>
 693        <para>
 694        __ata_qc_complete() is called, which does
 695           <orderedlist>
 696
 697           <listitem>
 698           <para>
 699           qc->flags is cleared to zero.
 700           </para>
 701           </listitem>
 702
 703           <listitem>
 704           <para>
 705           ap->active_tag and qc->tag are poisoned.
 706           </para>
 707           </listitem>
 708
 709           <listitem>
 710           <para>
 711           qc->waiting is claread &amp; completed (in that order).
 712           </para>
 713           </listitem>
 714
 715           <listitem>
 716           <para>
 717           qc is deallocated by clearing appropriate bit in ap->qactive.
 718           </para>
 719           </listitem>
 720
 721           </orderedlist>
 722        </para>
 723        </listitem>
 724
 725        </orderedlist>
 726
 727        <para>
 728        So, it basically notifies upper layer and deallocates qc.  One
 729        exception is short-circuit path in #3 which is used by
 730        atapi_qc_complete().
 731        </para>
 732        <para>
 733        For all non-ATAPI commands, whether it fails or not, almost
 734        the same code path is taken and very little error handling
 735        takes place.  A qc is completed with success status if it
 736        succeeded, with failed status otherwise.
 737        </para>
 738        <para>
 739        However, failed ATAPI commands require more handling as
 740        REQUEST SENSE is needed to acquire sense data.  If an ATAPI
 741        command fails, ata_qc_complete() is invoked with error status,
 742        which in turn invokes atapi_qc_complete() via
 743        qc->complete_fn() callback.
 744        </para>
 745        <para>
 746        This makes atapi_qc_complete() set scmd->result to
 747        SAM_STAT_CHECK_CONDITION, complete the scmd and return 1.  As
 748        the sense data is empty but scmd->result is CHECK CONDITION,
 749        SCSI midlayer will invoke EH for the scmd, and returning 1
 750        makes ata_qc_complete() to return without deallocating the qc.
 751        This leads us to ata_scsi_error() with partially completed qc.
 752        </para>
 753
 754        </sect1>
 755
 756        <sect1><title>ata_scsi_error()</title>
 757        <para>
 758        ata_scsi_error() is the current transportt->eh_strategy_handler()
 759        for libata.  As discussed above, this will be entered in two
 760        cases - timeout and ATAPI error completion.  This function
 761        calls low level libata driver's eng_timeout() callback, the
 762        standard callback for which is ata_eng_timeout().  It checks
 763        if a qc is active and calls ata_qc_timeout() on the qc if so.
 764        Actual error handling occurs in ata_qc_timeout().
 765        </para>
 766        <para>
 767        If EH is invoked for timeout, ata_qc_timeout() stops BMDMA and
 768        completes the qc.  Note that as we're currently in EH, we
 769        cannot call scsi_done.  As described in SCSI EH doc, a
 770        recovered scmd should be either retried with
 771        scsi_queue_insert() or finished with scsi_finish_command().
 772        Here, we override qc->scsidone with scsi_finish_command() and
 773        calls ata_qc_complete().
 774        </para>
 775        <para>
 776        If EH is invoked due to a failed ATAPI qc, the qc here is
 777        completed but not deallocated.  The purpose of this
 778        half-completion is to use the qc as place holder to make EH
 779        code reach this place.  This is a bit hackish, but it works.
 780        </para>
 781        <para>
 782        Once control reaches here, the qc is deallocated by invoking
 783        __ata_qc_complete() explicitly.  Then, internal qc for REQUEST
 784        SENSE is issued.  Once sense data is acquired, scmd is
 785        finished by directly invoking scsi_finish_command() on the
 786        scmd.  Note that as we already have completed and deallocated
 787        the qc which was associated with the scmd, we don't need
 788        to/cannot call ata_qc_complete() again.
 789        </para>
 790
 791        </sect1>
 792
 793        <sect1><title>Problems with the current EH</title>
 794
 795        <itemizedlist>
 796
 797        <listitem>
 798        <para>
 799        Error representation is too crude.  Currently any and all
 800        error conditions are represented with ATA STATUS and ERROR
 801        registers.  Errors which aren't ATA device errors are treated
 802        as ATA device errors by setting ATA_ERR bit.  Better error
 803        descriptor which can properly represent ATA and other
 804        errors/exceptions is needed.
 805        </para>
 806        </listitem>
 807
 808        <listitem>
 809        <para>
 810        When handling timeouts, no action is taken to make device
 811        forget about the timed out command and ready for new commands.
 812        </para>
 813        </listitem>
 814
 815        <listitem>
 816        <para>
 817        EH handling via ata_scsi_error() is not properly protected
 818        from usual command processing.  On EH entrance, the device is
 819        not in quiescent state.  Timed out commands may succeed or
 820        fail any time.  pio_task and atapi_task may still be running.
 821        </para>
 822        </listitem>
 823
 824        <listitem>
 825        <para>
 826        Too weak error recovery.  Devices / controllers causing HSM
 827        mismatch errors and other errors quite often require reset to
 828        return to known state.  Also, advanced error handling is
 829        necessary to support features like NCQ and hotplug.
 830        </para>
 831        </listitem>
 832
 833        <listitem>
 834        <para>
 835        ATA errors are directly handled in the interrupt handler and
 836        PIO errors in pio_task.  This is problematic for advanced
 837        error handling for the following reasons.
 838        </para>
 839        <para>
 840        First, advanced error handling often requires context and
 841        internal qc execution.
 842        </para>
 843        <para>
 844        Second, even a simple failure (say, CRC error) needs
 845        information gathering and could trigger complex error handling
 846        (say, resetting &amp; reconfiguring).  Having multiple code
 847        paths to gather information, enter EH and trigger actions
 848        makes life painful.
 849        </para>
 850        <para>
 851        Third, scattered EH code makes implementing low level drivers
 852        difficult.  Low level drivers override libata callbacks.  If
 853        EH is scattered over several places, each affected callbacks
 854        should perform its part of error handling.  This can be error
 855        prone and painful.
 856        </para>
 857        </listitem>
 858
 859        </itemizedlist>
 860        </sect1>
 861  </chapter>
 862
 863  <chapter id="libataExt">
 864     <title>libata Library</title>
 865!Edrivers/ata/libata-core.c
 866  </chapter>
 867
 868  <chapter id="libataInt">
 869     <title>libata Core Internals</title>
 870!Idrivers/ata/libata-core.c
 871  </chapter>
 872
 873  <chapter id="libataScsiInt">
 874     <title>libata SCSI translation/emulation</title>
 875!Edrivers/ata/libata-scsi.c
 876!Idrivers/ata/libata-scsi.c
 877  </chapter>
 878
 879  <chapter id="ataExceptions">
 880     <title>ATA errors and exceptions</title>
 881
 882  <para>
 883  This chapter tries to identify what error/exception conditions exist
 884  for ATA/ATAPI devices and describe how they should be handled in
 885  implementation-neutral way.
 886  </para>
 887
 888  <para>
 889  The term 'error' is used to describe conditions where either an
 890  explicit error condition is reported from device or a command has
 891  timed out.
 892  </para>
 893
 894  <para>
 895  The term 'exception' is either used to describe exceptional
 896  conditions which are not errors (say, power or hotplug events), or
 897  to describe both errors and non-error exceptional conditions.  Where
 898  explicit distinction between error and exception is necessary, the
 899  term 'non-error exception' is used.
 900  </para>
 901
 902  <sect1 id="excat">
 903     <title>Exception categories</title>
 904     <para>
 905     Exceptions are described primarily with respect to legacy
 906     taskfile + bus master IDE interface.  If a controller provides
 907     other better mechanism for error reporting, mapping those into
 908     categories described below shouldn't be difficult.
 909     </para>
 910
 911     <para>
 912     In the following sections, two recovery actions - reset and
 913     reconfiguring transport - are mentioned.  These are described
 914     further in <xref linkend="exrec"/>.
 915     </para>
 916
 917     <sect2 id="excatHSMviolation">
 918        <title>HSM violation</title>
 919        <para>
 920        This error is indicated when STATUS value doesn't match HSM
 921        requirement during issuing or execution any ATA/ATAPI command.
 922        </para>
 923
 924        <itemizedlist>
 925        <title>Examples</title>
 926
 927        <listitem>
 928        <para>
 929        ATA_STATUS doesn't contain !BSY &amp;&amp; DRDY &amp;&amp; !DRQ while trying
 930        to issue a command.
 931        </para>
 932        </listitem>
 933
 934        <listitem>
 935        <para>
 936        !BSY &amp;&amp; !DRQ during PIO data transfer.
 937        </para>
 938        </listitem>
 939
 940        <listitem>
 941        <para>
 942        DRQ on command completion.
 943        </para>
 944        </listitem>
 945
 946        <listitem>
 947        <para>
 948        !BSY &amp;&amp; ERR after CDB transfer starts but before the
 949        last byte of CDB is transferred.  ATA/ATAPI standard states
 950        that &quot;The device shall not terminate the PACKET command
 951        with an error before the last byte of the command packet has
 952        been written&quot; in the error outputs description of PACKET
 953        command and the state diagram doesn't include such
 954        transitions.
 955        </para>
 956        </listitem>
 957
 958        </itemizedlist>
 959
 960        <para>
 961        In these cases, HSM is violated and not much information
 962        regarding the error can be acquired from STATUS or ERROR
 963        register.  IOW, this error can be anything - driver bug,
 964        faulty device, controller and/or cable.
 965        </para>
 966
 967        <para>
 968        As HSM is violated, reset is necessary to restore known state.
 969        Reconfiguring transport for lower speed might be helpful too
 970        as transmission errors sometimes cause this kind of errors.
 971        </para>
 972     </sect2>
 973     
 974     <sect2 id="excatDevErr">
 975        <title>ATA/ATAPI device error (non-NCQ / non-CHECK CONDITION)</title>
 976
 977        <para>
 978        These are errors detected and reported by ATA/ATAPI devices
 979        indicating device problems.  For this type of errors, STATUS
 980        and ERROR register values are valid and describe error
 981        condition.  Note that some of ATA bus errors are detected by
 982        ATA/ATAPI devices and reported using the same mechanism as
 983        device errors.  Those cases are described later in this
 984        section.
 985        </para>
 986
 987        <para>
 988        For ATA commands, this type of errors are indicated by !BSY
 989        &amp;&amp; ERR during command execution and on completion.
 990        </para>
 991
 992        <para>For ATAPI commands,</para>
 993
 994        <itemizedlist>
 995
 996        <listitem>
 997        <para>
 998        !BSY &amp;&amp; ERR &amp;&amp; ABRT right after issuing PACKET
 999        indicates that PACKET command is not supported and falls in
1000        this category.
1001        </para>
1002        </listitem>
1003
1004        <listitem>
1005        <para>
1006        !BSY &amp;&amp; ERR(==CHK) &amp;&amp; !ABRT after the last
1007        byte of CDB is transferred indicates CHECK CONDITION and
1008        doesn't fall in this category.
1009        </para>
1010        </listitem>
1011
1012        <listitem>
1013        <para>
1014        !BSY &amp;&amp; ERR(==CHK) &amp;&amp; ABRT after the last byte
1015        of CDB is transferred *probably* indicates CHECK CONDITION and
1016        doesn't fall in this category.
1017        </para>
1018        </listitem>
1019
1020        </itemizedlist>
1021
1022        <para>
1023        Of errors detected as above, the followings are not ATA/ATAPI
1024        device errors but ATA bus errors and should be handled
1025        according to <xref linkend="excatATAbusErr"/>.
1026        </para>
1027
1028        <variablelist>
1029
1030           <varlistentry>
1031           <term>CRC error during data transfer</term>
1032           <listitem>
1033           <para>
1034           This is indicated by ICRC bit in the ERROR register and
1035           means that corruption occurred during data transfer.  Up to
1036           ATA/ATAPI-7, the standard specifies that this bit is only
1037           applicable to UDMA transfers but ATA/ATAPI-8 draft revision
1038           1f says that the bit may be applicable to multiword DMA and
1039           PIO.
1040           </para>
1041           </listitem>
1042           </varlistentry>
1043
1044           <varlistentry>
1045           <term>ABRT error during data transfer or on completion</term>
1046           <listitem>
1047           <para>
1048           Up to ATA/ATAPI-7, the standard specifies that ABRT could be
1049           set on ICRC errors and on cases where a device is not able
1050           to complete a command.  Combined with the fact that MWDMA
1051           and PIO transfer errors aren't allowed to use ICRC bit up to
1052           ATA/ATAPI-7, it seems to imply that ABRT bit alone could
1053           indicate transfer errors.
1054           </para>
1055           <para>
1056           However, ATA/ATAPI-8 draft revision 1f removes the part
1057           that ICRC errors can turn on ABRT.  So, this is kind of
1058           gray area.  Some heuristics are needed here.
1059           </para>
1060           </listitem>
1061           </varlistentry>
1062
1063        </variablelist>
1064
1065        <para>
1066        ATA/ATAPI device errors can be further categorized as follows.
1067        </para>
1068
1069        <variablelist>
1070
1071           <varlistentry>
1072           <term>Media errors</term>
1073           <listitem>
1074           <para>
1075           This is indicated by UNC bit in the ERROR register.  ATA
1076           devices reports UNC error only after certain number of
1077           retries cannot recover the data, so there's nothing much
1078           else to do other than notifying upper layer.
1079           </para>
1080           <para>
1081           READ and WRITE commands report CHS or LBA of the first
1082           failed sector but ATA/ATAPI standard specifies that the
1083           amount of transferred data on error completion is
1084           indeterminate, so we cannot assume that sectors preceding
1085           the failed sector have been transferred and thus cannot
1086           complete those sectors successfully as SCSI does.
1087           </para>
1088           </listitem>
1089           </varlistentry>
1090
1091           <varlistentry>
1092           <term>Media changed / media change requested error</term>
1093           <listitem>
1094           <para>
1095           &lt;&lt;TODO: fill here&gt;&gt;
1096           </para>
1097           </listitem>
1098           </varlistentry>
1099
1100           <varlistentry><term>Address error</term>
1101           <listitem>
1102           <para>
1103           This is indicated by IDNF bit in the ERROR register.
1104           Report to upper layer.
1105           </para>
1106           </listitem>
1107           </varlistentry>
1108
1109           <varlistentry><term>Other errors</term>
1110           <listitem>
1111           <para>
1112           This can be invalid command or parameter indicated by ABRT
1113           ERROR bit or some other error condition.  Note that ABRT
1114           bit can indicate a lot of things including ICRC and Address
1115           errors.  Heuristics needed.
1116           </para>
1117           </listitem>
1118           </varlistentry>
1119
1120        </variablelist>
1121
1122        <para>
1123        Depending on commands, not all STATUS/ERROR bits are
1124        applicable.  These non-applicable bits are marked with
1125        &quot;na&quot; in the output descriptions but up to ATA/ATAPI-7
1126        no definition of &quot;na&quot; can be found.  However,
1127        ATA/ATAPI-8 draft revision 1f describes &quot;N/A&quot; as
1128        follows.
1129        </para>
1130
1131        <blockquote>
1132        <variablelist>
1133           <varlistentry><term>3.2.3.3a N/A</term>
1134           <listitem>
1135           <para>
1136           A keyword the indicates a field has no defined value in
1137           this standard and should not be checked by the host or
1138           device. N/A fields should be cleared to zero.
1139           </para>
1140           </listitem>
1141           </varlistentry>
1142        </variablelist>
1143        </blockquote>
1144
1145        <para>
1146        So, it seems reasonable to assume that &quot;na&quot; bits are
1147        cleared to zero by devices and thus need no explicit masking.
1148        </para>
1149
1150     </sect2>
1151
1152     <sect2 id="excatATAPIcc">
1153        <title>ATAPI device CHECK CONDITION</title>
1154
1155        <para>
1156        ATAPI device CHECK CONDITION error is indicated by set CHK bit
1157        (ERR bit) in the STATUS register after the last byte of CDB is
1158        transferred for a PACKET command.  For this kind of errors,
1159        sense data should be acquired to gather information regarding
1160        the errors.  REQUEST SENSE packet command should be used to
1161        acquire sense data.
1162        </para>
1163
1164        <para>
1165        Once sense data is acquired, this type of errors can be
1166        handled similary to other SCSI errors.  Note that sense data
1167        may indicate ATA bus error (e.g. Sense Key 04h HARDWARE ERROR
1168        &amp;&amp; ASC/ASCQ 47h/00h SCSI PARITY ERROR).  In such
1169        cases, the error should be considered as an ATA bus error and
1170        handled according to <xref linkend="excatATAbusErr"/>.
1171        </para>
1172
1173     </sect2>
1174
1175     <sect2 id="excatNCQerr">
1176        <title>ATA device error (NCQ)</title>
1177
1178        <para>
1179        NCQ command error is indicated by cleared BSY and set ERR bit
1180        during NCQ command phase (one or more NCQ commands
1181        outstanding).  Although STATUS and ERROR registers will
1182        contain valid values describing the error, READ LOG EXT is
1183        required to clear the error condition, determine which command
1184        has failed and acquire more information.
1185        </para>
1186
1187        <para>
1188        READ LOG EXT Log Page 10h reports which tag has failed and
1189        taskfile register values describing the error.  With this
1190        information the failed command can be handled as a normal ATA
1191        command error as in <xref linkend="excatDevErr"/> and all
1192        other in-flight commands must be retried.  Note that this
1193        retry should not be counted - it's likely that commands
1194        retried this way would have completed normally if it were not
1195        for the failed command.
1196        </para>
1197
1198        <para>
1199        Note that ATA bus errors can be reported as ATA device NCQ
1200        errors.  This should be handled as described in <xref
1201        linkend="excatATAbusErr"/>.
1202        </para>
1203
1204        <para>
1205        If READ LOG EXT Log Page 10h fails or reports NQ, we're
1206        thoroughly screwed.  This condition should be treated
1207        according to <xref linkend="excatHSMviolation"/>.
1208        </para>
1209
1210     </sect2>
1211
1212     <sect2 id="excatATAbusErr">
1213        <title>ATA bus error</title>
1214
1215        <para>
1216        ATA bus error means that data corruption occurred during
1217        transmission over ATA bus (SATA or PATA).  This type of errors
1218        can be indicated by
1219        </para>
1220
1221        <itemizedlist>
1222
1223        <listitem>
1224        <para>
1225        ICRC or ABRT error as described in <xref linkend="excatDevErr"/>.
1226        </para>
1227        </listitem>
1228
1229        <listitem>
1230        <para>
1231        Controller-specific error completion with error information
1232        indicating transmission error.
1233        </para>
1234        </listitem>
1235
1236        <listitem>
1237        <para>
1238        On some controllers, command timeout.  In this case, there may
1239        be a mechanism to determine that the timeout is due to
1240        transmission error.
1241        </para>
1242        </listitem>
1243
1244        <listitem>
1245        <para>
1246        Unknown/random errors, timeouts and all sorts of weirdities.
1247        </para>
1248        </listitem>
1249
1250        </itemizedlist>
1251
1252        <para>
1253        As described above, transmission errors can cause wide variety
1254        of symptoms ranging from device ICRC error to random device
1255        lockup, and, for many cases, there is no way to tell if an
1256        error condition is due to transmission error or not;
1257        therefore, it's necessary to employ some kind of heuristic
1258        when dealing with errors and timeouts.  For example,
1259        encountering repetitive ABRT errors for known supported
1260        command is likely to indicate ATA bus error.
1261        </para>
1262
1263        <para>
1264        Once it's determined that ATA bus errors have possibly
1265        occurred, lowering ATA bus transmission speed is one of
1266        actions which may alleviate the problem.  See <xref
1267        linkend="exrecReconf"/> for more information.
1268        </para>
1269
1270     </sect2>
1271
1272     <sect2 id="excatPCIbusErr">
1273        <title>PCI bus error</title>
1274
1275        <para>
1276        Data corruption or other failures during transmission over PCI
1277        (or other system bus).  For standard BMDMA, this is indicated
1278        by Error bit in the BMDMA Status register.  This type of
1279        errors must be logged as it indicates something is very wrong
1280        with the system.  Resetting host controller is recommended.
1281        </para>
1282
1283     </sect2>
1284
1285     <sect2 id="excatLateCompletion">
1286        <title>Late completion</title>
1287
1288        <para>
1289        This occurs when timeout occurs and the timeout handler finds
1290        out that the timed out command has completed successfully or
1291        with error.  This is usually caused by lost interrupts.  This
1292        type of errors must be logged.  Resetting host controller is
1293        recommended.
1294        </para>
1295
1296     </sect2>
1297
1298     <sect2 id="excatUnknown">
1299        <title>Unknown error (timeout)</title>
1300
1301        <para>
1302        This is when timeout occurs and the command is still
1303        processing or the host and device are in unknown state.  When
1304        this occurs, HSM could be in any valid or invalid state.  To
1305        bring the device to known state and make it forget about the
1306        timed out command, resetting is necessary.  The timed out
1307        command may be retried.
1308        </para>
1309
1310        <para>
1311        Timeouts can also be caused by transmission errors.  Refer to
1312        <xref linkend="excatATAbusErr"/> for more details.
1313        </para>
1314
1315     </sect2>
1316
1317     <sect2 id="excatHoplugPM">
1318        <title>Hotplug and power management exceptions</title>
1319
1320        <para>
1321        &lt;&lt;TODO: fill here&gt;&gt;
1322        </para>
1323
1324     </sect2>
1325
1326  </sect1>
1327
1328  <sect1 id="exrec">
1329     <title>EH recovery actions</title>
1330
1331     <para>
1332     This section discusses several important recovery actions.
1333     </para>
1334
1335     <sect2 id="exrecClr">
1336        <title>Clearing error condition</title>
1337
1338        <para>
1339        Many controllers require its error registers to be cleared by
1340        error handler.  Different controllers may have different
1341        requirements.
1342        </para>
1343
1344        <para>
1345        For SATA, it's strongly recommended to clear at least SError
1346        register during error handling.
1347        </para>
1348     </sect2>
1349
1350     <sect2 id="exrecRst">
1351        <title>Reset</title>
1352
1353        <para>
1354        During EH, resetting is necessary in the following cases.
1355        </para>
1356
1357        <itemizedlist>
1358
1359        <listitem>
1360        <para>
1361        HSM is in unknown or invalid state
1362        </para>
1363        </listitem>
1364
1365        <listitem>
1366        <para>
1367        HBA is in unknown or invalid state
1368        </para>
1369        </listitem>
1370
1371        <listitem>
1372        <para>
1373        EH needs to make HBA/device forget about in-flight commands
1374        </para>
1375        </listitem>
1376
1377        <listitem>
1378        <para>
1379        HBA/device behaves weirdly
1380        </para>
1381        </listitem>
1382
1383        </itemizedlist>
1384
1385        <para>
1386        Resetting during EH might be a good idea regardless of error
1387        condition to improve EH robustness.  Whether to reset both or
1388        either one of HBA and device depends on situation but the
1389        following scheme is recommended.
1390        </para>
1391
1392        <itemizedlist>
1393
1394        <listitem>
1395        <para>
1396        When it's known that HBA is in ready state but ATA/ATAPI
1397        device is in unknown state, reset only device.
1398        </para>
1399        </listitem>
1400
1401        <listitem>
1402        <para>
1403        If HBA is in unknown state, reset both HBA and device.
1404        </para>
1405        </listitem>
1406
1407        </itemizedlist>
1408
1409        <para>
1410        HBA resetting is implementation specific.  For a controller
1411        complying to taskfile/BMDMA PCI IDE, stopping active DMA
1412        transaction may be sufficient iff BMDMA state is the only HBA
1413        context.  But even mostly taskfile/BMDMA PCI IDE complying
1414        controllers may have implementation specific requirements and
1415        mechanism to reset themselves.  This must be addressed by
1416        specific drivers.
1417        </para>
1418
1419        <para>
1420        OTOH, ATA/ATAPI standard describes in detail ways to reset
1421        ATA/ATAPI devices.
1422        </para>
1423
1424        <variablelist>
1425
1426           <varlistentry><term>PATA hardware reset</term>
1427           <listitem>
1428           <para>
1429           This is hardware initiated device reset signalled with
1430           asserted PATA RESET- signal.  There is no standard way to
1431           initiate hardware reset from software although some
1432           hardware provides registers that allow driver to directly
1433           tweak the RESET- signal.
1434           </para>
1435           </listitem>
1436           </varlistentry>
1437
1438           <varlistentry><term>Software reset</term>
1439           <listitem>
1440           <para>
1441           This is achieved by turning CONTROL SRST bit on for at
1442           least 5us.  Both PATA and SATA support it but, in case of
1443           SATA, this may require controller-specific support as the
1444           second Register FIS to clear SRST should be transmitted
1445           while BSY bit is still set.  Note that on PATA, this resets
1446           both master and slave devices on a channel.
1447           </para>
1448           </listitem>
1449           </varlistentry>
1450
1451           <varlistentry><term>EXECUTE DEVICE DIAGNOSTIC command</term>
1452           <listitem>
1453           <para>
1454           Although ATA/ATAPI standard doesn't describe exactly, EDD
1455           implies some level of resetting, possibly similar level
1456           with software reset.  Host-side EDD protocol can be handled
1457           with normal command processing and most SATA controllers
1458           should be able to handle EDD's just like other commands.
1459           As in software reset, EDD affects both devices on a PATA
1460           bus.
1461           </para>
1462           <para>
1463           Although EDD does reset devices, this doesn't suit error
1464           handling as EDD cannot be issued while BSY is set and it's
1465           unclear how it will act when device is in unknown/weird
1466           state.
1467           </para>
1468           </listitem>
1469           </varlistentry>
1470
1471           <varlistentry><term>ATAPI DEVICE RESET command</term>
1472           <listitem>
1473           <para>
1474           This is very similar to software reset except that reset
1475           can be restricted to the selected device without affecting
1476           the other device sharing the cable.
1477           </para>
1478           </listitem>
1479           </varlistentry>
1480
1481           <varlistentry><term>SATA phy reset</term>
1482           <listitem>
1483           <para>
1484           This is the preferred way of resetting a SATA device.  In
1485           effect, it's identical to PATA hardware reset.  Note that
1486           this can be done with the standard SCR Control register.
1487           As such, it's usually easier to implement than software
1488           reset.
1489           </para>
1490           </listitem>
1491           </varlistentry>
1492
1493        </variablelist>
1494
1495        <para>
1496        One more thing to consider when resetting devices is that
1497        resetting clears certain configuration parameters and they
1498        need to be set to their previous or newly adjusted values
1499        after reset.
1500        </para>
1501
1502        <para>
1503        Parameters affected are.
1504        </para>
1505
1506        <itemizedlist>
1507
1508        <listitem>
1509        <para>
1510        CHS set up with INITIALIZE DEVICE PARAMETERS (seldom used)
1511        </para>
1512        </listitem>
1513
1514        <listitem>
1515        <para>
1516        Parameters set with SET FEATURES including transfer mode setting
1517        </para>
1518        </listitem>
1519
1520        <listitem>
1521        <para>
1522        Block count set with SET MULTIPLE MODE
1523        </para>
1524        </listitem>
1525
1526        <listitem>
1527        <para>
1528        Other parameters (SET MAX, MEDIA LOCK...)
1529        </para>
1530        </listitem>
1531
1532        </itemizedlist>
1533
1534        <para>
1535        ATA/ATAPI standard specifies that some parameters must be
1536        maintained across hardware or software reset, but doesn't
1537        strictly specify all of them.  Always reconfiguring needed
1538        parameters after reset is required for robustness.  Note that
1539        this also applies when resuming from deep sleep (power-off).
1540        </para>
1541
1542        <para>
1543        Also, ATA/ATAPI standard requires that IDENTIFY DEVICE /
1544        IDENTIFY PACKET DEVICE is issued after any configuration
1545        parameter is updated or a hardware reset and the result used
1546        for further operation.  OS driver is required to implement
1547        revalidation mechanism to support this.
1548        </para>
1549
1550     </sect2>
1551
1552     <sect2 id="exrecReconf">
1553        <title>Reconfigure transport</title>
1554
1555        <para>
1556        For both PATA and SATA, a lot of corners are cut for cheap
1557        connectors, cables or controllers and it's quite common to see
1558        high transmission error rate.  This can be mitigated by
1559        lowering transmission speed.
1560        </para>
1561
1562        <para>
1563        The following is a possible scheme Jeff Garzik suggested.
1564        </para>
1565
1566        <blockquote>
1567        <para>
1568        If more than $N (3?) transmission errors happen in 15 minutes,
1569        </para> 
1570        <itemizedlist>
1571        <listitem>
1572        <para>
1573        if SATA, decrease SATA PHY speed.  if speed cannot be decreased,
1574        </para>
1575        </listitem>
1576        <listitem>
1577        <para>
1578        decrease UDMA xfer speed.  if at UDMA0, switch to PIO4,
1579        </para>
1580        </listitem>
1581        <listitem>
1582        <para>
1583        decrease PIO xfer speed.  if at PIO3, complain, but continue
1584        </para>
1585        </listitem>
1586        </itemizedlist>
1587        </blockquote>
1588
1589     </sect2>
1590
1591  </sect1>
1592
1593  </chapter>
1594
1595  <chapter id="PiixInt">
1596     <title>ata_piix Internals</title>
1597!Idrivers/ata/ata_piix.c
1598  </chapter>
1599
1600  <chapter id="SILInt">
1601     <title>sata_sil Internals</title>
1602!Idrivers/ata/sata_sil.c
1603  </chapter>
1604
1605  <chapter id="libataThanks">
1606     <title>Thanks</title>
1607  <para>
1608  The bulk of the ATA knowledge comes thanks to long conversations with
1609  Andre Hedrick (www.linux-ide.org), and long hours pondering the ATA
1610  and SCSI specifications.
1611  </para>
1612  <para>
1613  Thanks to Alan Cox for pointing out similarities 
1614  between SATA and SCSI, and in general for motivation to hack on
1615  libata.
1616  </para>
1617  <para>
1618  libata's device detection
1619  method, ata_pio_devchk, and in general all the early probing was
1620  based on extensive study of Hale Landis's probe/reset code in his
1621  ATADRVR driver (www.ata-atapi.com).
1622  </para>
1623  </chapter>
1624
1625</book>
1626
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