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://www.opensource.org/licenses/osl-1.1.txt">http://www.opensource.org/licenses/osl-1.1.txt</ulink> and is included herein 26 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<->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() and ata_bus_reset() error paths, 85 as well as when unregistering from the SCSI module (rmmod, hot 86 unplug). 87 This function should do whatever needs to be done to take the 88 port out of use. In most cases, ata_port_disable() can be used 89 as this hook. 90 </para> 91 <para> 92 Called from ata_bus_probe() on a failed probe. 93 Called from ata_bus_reset() on a failed bus reset. 94 Called from ata_scsi_release(). 95 </para> 96 97 </sect2> 98 99 <sect2><title>Post-IDENTIFY device configuration</title> 100 <programlisting> 101void (*dev_config) (struct ata_port *, struct ata_device *); 102 </programlisting> 103 104 <para> 105 Called after IDENTIFY [PACKET] DEVICE is issued to each device 106 found. Typically used to apply device-specific fixups prior to 107 issue of SET FEATURES - XFER MODE, and prior to operation. 108 </para> 109 <para> 110 Called by ata_device_add() after ata_dev_identify() determines 111 a device is present. 112 </para> 113 <para> 114 This entry may be specified as NULL in ata_port_operations. 115 </para> 116 117 </sect2> 118 119 <sect2><title>Set PIO/DMA mode</title> 120 <programlisting> 121void (*set_piomode) (struct ata_port *, struct ata_device *); 122void (*set_dmamode) (struct ata_port *, struct ata_device *); 123void (*post_set_mode) (struct ata_port *); 124unsigned int (*mode_filter) (struct ata_port *, struct ata_device *, unsigned int); 125 </programlisting> 126 127 <para> 128 Hooks called prior to the issue of SET FEATURES - XFER MODE 129 command. The optional ->mode_filter() hook is called when libata 130 has built a mask of the possible modes. This is passed to the 131 ->mode_filter() function which should return a mask of valid modes 132 after filtering those unsuitable due to hardware limits. It is not 133 valid to use this interface to add modes. 134 </para> 135 <para> 136 dev->pio_mode and dev->dma_mode are guaranteed to be valid when 137 ->set_piomode() and when ->set_dmamode() is called. The timings for 138 any other drive sharing the cable will also be valid at this point. 139 That is the library records the decisions for the modes of each 140 drive on a channel before it attempts to set any of them. 141 </para> 142 <para> 143 ->post_set_mode() is 144 called unconditionally, after the SET FEATURES - XFER MODE 145 command completes successfully. 146 </para> 147 148 <para> 149 ->set_piomode() is always called (if present), but 150 ->set_dma_mode() is only called if DMA is possible. 151 </para> 152 153 </sect2> 154 155 <sect2><title>Taskfile read/write</title> 156 <programlisting> 157void (*tf_load) (struct ata_port *ap, struct ata_taskfile *tf); 158void (*tf_read) (struct ata_port *ap, struct ata_taskfile *tf); 159 </programlisting> 160 161 <para> 162 ->tf_load() is called to load the given taskfile into hardware 163 registers / DMA buffers. ->tf_read() is called to read the 164 hardware registers / DMA buffers, to obtain the current set of 165 taskfile register values. 166 Most drivers for taskfile-based hardware (PIO or MMIO) use 167 ata_tf_load() and ata_tf_read() for these hooks. 168 </para> 169 170 </sect2> 171 172 <sect2><title>PIO data read/write</title> 173 <programlisting> 174void (*data_xfer) (struct ata_device *, unsigned char *, unsigned int, int); 175 </programlisting> 176 177 <para> 178All bmdma-style drivers must implement this hook. This is the low-level 179operation that actually copies the data bytes during a PIO data 180transfer. 181Typically the driver 182will choose one of ata_pio_data_xfer_noirq(), ata_pio_data_xfer(), or 183ata_mmio_data_xfer(). 184 </para> 185 186 </sect2> 187 188 <sect2><title>ATA command execute</title> 189 <programlisting> 190void (*exec_command)(struct ata_port *ap, struct ata_taskfile *tf); 191 </programlisting> 192 193 <para> 194 causes an ATA command, previously loaded with 195 ->tf_load(), to be initiated in hardware. 196 Most drivers for taskfile-based hardware use ata_exec_command() 197 for this hook. 198 </para> 199 200 </sect2> 201 202 <sect2><title>Per-cmd ATAPI DMA capabilities filter</title> 203 <programlisting> 204int (*check_atapi_dma) (struct ata_queued_cmd *qc); 205 </programlisting> 206 207 <para> 208Allow low-level driver to filter ATA PACKET commands, returning a status 209indicating whether or not it is OK to use DMA for the supplied PACKET 210command. 211 </para> 212 <para> 213 This hook may be specified as NULL, in which case libata will 214 assume that atapi dma can be supported. 215 </para> 216 217 </sect2> 218 219 <sect2><title>Read specific ATA shadow registers</title> 220 <programlisting> 221u8 (*check_status)(struct ata_port *ap); 222u8 (*check_altstatus)(struct ata_port *ap); 223 </programlisting> 224 225 <para> 226 Reads the Status/AltStatus ATA shadow register from 227 hardware. On some hardware, reading the Status register has 228 the side effect of clearing the interrupt condition. 229 Most drivers for taskfile-based hardware use 230 ata_check_status() for this hook. 231 </para> 232 <para> 233 Note that because this is called from ata_device_add(), at 234 least a dummy function that clears device interrupts must be 235 provided for all drivers, even if the controller doesn't 236 actually have a taskfile status register. 237 </para> 238 239 </sect2> 240 241 <sect2><title>Select ATA device on bus</title> 242 <programlisting> 243void (*dev_select)(struct ata_port *ap, unsigned int device); 244 </programlisting> 245 246 <para> 247 Issues the low-level hardware command(s) that causes one of N 248 hardware devices to be considered 'selected' (active and 249 available for use) on the ATA bus. This generally has no 250 meaning on FIS-based devices. 251 </para> 252 <para> 253 Most drivers for taskfile-based hardware use 254 ata_std_dev_select() for this hook. Controllers which do not 255 support second drives on a port (such as SATA contollers) will 256 use ata_noop_dev_select(). 257 </para> 258 259 </sect2> 260 261 <sect2><title>Private tuning method</title> 262 <programlisting> 263void (*set_mode) (struct ata_port *ap); 264 </programlisting> 265 266 <para> 267 By default libata performs drive and controller tuning in 268 accordance with the ATA timing rules and also applies blacklists 269 and cable limits. Some controllers need special handling and have 270 custom tuning rules, typically raid controllers that use ATA 271 commands but do not actually do drive timing. 272 </para> 273 274 <warning> 275 <para> 276 This hook should not be used to replace the standard controller 277 tuning logic when a controller has quirks. Replacing the default 278 tuning logic in that case would bypass handling for drive and 279 bridge quirks that may be important to data reliability. If a 280 controller needs to filter the mode selection it should use the 281 mode_filter hook instead. 282 </para> 283 </warning> 284 285 </sect2> 286 287 <sect2><title>Control PCI IDE BMDMA engine</title> 288 <programlisting> 289void (*bmdma_setup) (struct ata_queued_cmd *qc); 290void (*bmdma_start) (struct ata_queued_cmd *qc); 291void (*bmdma_stop) (struct ata_port *ap); 292u8 (*bmdma_status) (struct ata_port *ap); 293 </programlisting> 294 295 <para> 296When setting up an IDE BMDMA transaction, these hooks arm 297(->bmdma_setup), fire (->bmdma_start), and halt (->bmdma_stop) 298the hardware's DMA engine. ->bmdma_status is used to read the standard 299PCI IDE DMA Status register. 300 </para> 301 302 <para> 303These hooks are typically either no-ops, or simply not implemented, in 304FIS-based drivers. 305 </para> 306 <para> 307Most legacy IDE drivers use ata_bmdma_setup() for the bmdma_setup() 308hook. ata_bmdma_setup() will write the pointer to the PRD table to 309the IDE PRD Table Address register, enable DMA in the DMA Command 310register, and call exec_command() to begin the transfer. 311 </para> 312 <para> 313Most legacy IDE drivers use ata_bmdma_start() for the bmdma_start() 314hook. ata_bmdma_start() will write the ATA_DMA_START flag to the DMA 315Command register. 316 </para> 317 <para> 318Many legacy IDE drivers use ata_bmdma_stop() for the bmdma_stop() 319hook. ata_bmdma_stop() clears the ATA_DMA_START flag in the DMA 320command register. 321 </para> 322 <para> 323Many legacy IDE drivers use ata_bmdma_status() as the bmdma_status() hook. 324 </para> 325 326 </sect2> 327 328 <sect2><title>High-level taskfile hooks</title> 329 <programlisting> 330void (*qc_prep) (struct ata_queued_cmd *qc); 331int (*qc_issue) (struct ata_queued_cmd *qc); 332 </programlisting> 333 334 <para> 335 Higher-level hooks, these two hooks can potentially supercede 336 several of the above taskfile/DMA engine hooks. ->qc_prep is 337 called after the buffers have been DMA-mapped, and is typically 338 used to populate the hardware's DMA scatter-gather table. 339 Most drivers use the standard ata_qc_prep() helper function, but 340 more advanced drivers roll their own. 341 </para> 342 <para> 343 ->qc_issue is used to make a command active, once the hardware 344 and S/G tables have been prepared. IDE BMDMA drivers use the 345 helper function ata_qc_issue_prot() for taskfile protocol-based 346 dispatch. More advanced drivers implement their own ->qc_issue. 347 </para> 348 <para> 349 ata_qc_issue_prot() calls ->tf_load(), ->bmdma_setup(), and 350 ->bmdma_start() as necessary to initiate a transfer. 351 </para> 352 353 </sect2> 354 355 <sect2><title>Exception and probe handling (EH)</title> 356 <programlisting> 357void (*eng_timeout) (struct ata_port *ap); 358void (*phy_reset) (struct ata_port *ap); 359 </programlisting> 360 361 <para> 362Deprecated. Use ->error_handler() instead. 363 </para> 364 365 <programlisting> 366void (*freeze) (struct ata_port *ap); 367void (*thaw) (struct ata_port *ap); 368 </programlisting> 369 370 <para> 371ata_port_freeze() is called when HSM violations or some other 372condition disrupts normal operation of the port. A frozen port 373is not allowed to perform any operation until the port is 374thawed, which usually follows a successful reset. 375 </para> 376 377 <para> 378The optional ->freeze() callback can be used for freezing the port 379hardware-wise (e.g. mask interrupt and stop DMA engine). If a 380port cannot be frozen hardware-wise, the interrupt handler 381must ack and clear interrupts unconditionally while the port 382is frozen. 383 </para> 384 <para> 385The optional ->thaw() callback is called to perform the opposite of ->freeze(): 386prepare the port for normal operation once again. Unmask interrupts, 387start DMA engine, etc. 388 </para> 389 390 <programlisting> 391void (*error_handler) (struct ata_port *ap); 392 </programlisting> 393 394 <para> 395->error_handler() is a driver's hook into probe, hotplug, and recovery 396and other exceptional conditions. The primary responsibility of an 397implementation is to call ata_do_eh() or ata_bmdma_drive_eh() with a set 398of EH hooks as arguments: 399 </para> 400 401 <para> 402'prereset' hook (may be NULL) is called during an EH reset, before any other actions 403are taken. 404 </para> 405 406 <para> 407'postreset' hook (may be NULL) is called after the EH reset is performed. Based on 408existing conditions, severity of the problem, and hardware capabilities, 409 </para> 410 411 <para> 412Either 'softreset' (may be NULL) or 'hardreset' (may be NULL) will be 413called to perform the low-level EH reset. 414 </para> 415 416 <programlisting> 417void (*post_internal_cmd) (struct ata_queued_cmd *qc); 418 </programlisting> 419 420 <para> 421Perform any hardware-specific actions necessary to finish processing 422after executing a probe-time or EH-time command via ata_exec_internal(). 423 </para> 424 425 </sect2> 426 427 <sect2><title>Hardware interrupt handling</title> 428 <programlisting> 429irqreturn_t (*irq_handler)(int, void *, struct pt_regs *); 430void (*irq_clear) (struct ata_port *); 431 </programlisting> 432 433 <para> 434 ->irq_handler is the interrupt handling routine registered with 435 the system, by libata. ->irq_clear is called during probe just 436 before the interrupt handler is registered, to be sure hardware 437 is quiet. 438 </para> 439 <para> 440 The second argument, dev_instance, should be cast to a pointer 441 to struct ata_host_set. 442 </para> 443 <para> 444 Most legacy IDE drivers use ata_interrupt() for the 445 irq_handler hook, which scans all ports in the host_set, 446 determines which queued command was active (if any), and calls 447 ata_host_intr(ap,qc). 448 </para> 449 <para> 450 Most legacy IDE drivers use ata_bmdma_irq_clear() for the 451 irq_clear() hook, which simply clears the interrupt and error 452 flags in the DMA status register. 453 </para> 454 455 </sect2> 456 457 <sect2><title>SATA phy read/write</title> 458 <programlisting> 459int (*scr_read) (struct ata_port *ap, unsigned int sc_reg, 460 u32 *val); 461int (*scr_write) (struct ata_port *ap, unsigned int sc_reg, 462 u32 val); 463 </programlisting> 464 465 <para> 466 Read and write standard SATA phy registers. Currently only used 467 if ->phy_reset hook called the sata_phy_reset() helper function. 468 sc_reg is one of SCR_STATUS, SCR_CONTROL, SCR_ERROR, or SCR_ACTIVE. 469 </para> 470 471 </sect2> 472 473 <sect2><title>Init and shutdown</title> 474 <programlisting> 475int (*port_start) (struct ata_port *ap); 476void (*port_stop) (struct ata_port *ap); 477void (*host_stop) (struct ata_host_set *host_set); 478 </programlisting> 479 480 <para> 481 ->port_start() is called just after the data structures for each 482 port are initialized. Typically this is used to alloc per-port 483 DMA buffers / tables / rings, enable DMA engines, and similar 484 tasks. Some drivers also use this entry point as a chance to 485 allocate driver-private memory for ap->private_data. 486 </para> 487 <para> 488 Many drivers use ata_port_start() as this hook or call 489 it from their own port_start() hooks. ata_port_start() 490 allocates space for a legacy IDE PRD table and returns. 491 </para> 492 <para> 493 ->port_stop() is called after ->host_stop(). It's sole function 494 is to release DMA/memory resources, now that they are no longer 495 actively being used. Many drivers also free driver-private 496 data from port at this time. 497 </para> 498 <para> 499 Many drivers use ata_port_stop() as this hook, which frees the 500 PRD table. 501 </para> 502 <para> 503 ->host_stop() is called after all ->port_stop() calls 504have completed. The hook must finalize hardware shutdown, release DMA 505and other resources, etc. 506 This hook may be specified as NULL, in which case it is not called. 507 </para> 508 509 </sect2> 510 511 </sect1> 512 </chapter> 513 514 <chapter id="libataEH"> 515 <title>Error handling</title> 516 517 <para> 518 This chapter describes how errors are handled under libata. 519 Readers are advised to read SCSI EH 520 (Documentation/scsi/scsi_eh.txt) and ATA exceptions doc first. 521 </para> 522 523 <sect1><title>Origins of commands</title> 524 <para> 525 In libata, a command is represented with struct ata_queued_cmd 526 or qc. qc's are preallocated during port initialization and 527 repetitively used for command executions. Currently only one 528 qc is allocated per port but yet-to-be-merged NCQ branch 529 allocates one for each tag and maps each qc to NCQ tag 1-to-1. 530 </para> 531 <para> 532 libata commands can originate from two sources - libata itself 533 and SCSI midlayer. libata internal commands are used for 534 initialization and error handling. All normal blk requests 535 and commands for SCSI emulation are passed as SCSI commands 536 through queuecommand callback of SCSI host template. 537 </para> 538 </sect1> 539 540 <sect1><title>How commands are issued</title> 541 542 <variablelist> 543 544 <varlistentry><term>Internal commands</term> 545 <listitem> 546 <para> 547 First, qc is allocated and initialized using 548 ata_qc_new_init(). Although ata_qc_new_init() doesn't 549 implement any wait or retry mechanism when qc is not 550 available, internal commands are currently issued only during 551 initialization and error recovery, so no other command is 552 active and allocation is guaranteed to succeed. 553 </para> 554 <para> 555 Once allocated qc's taskfile is initialized for the command to 556 be executed. qc currently has two mechanisms to notify 557 completion. One is via qc->complete_fn() callback and the 558 other is completion qc->waiting. qc->complete_fn() callback 559 is the asynchronous path used by normal SCSI translated 560 commands and qc->waiting is the synchronous (issuer sleeps in 561 process context) path used by internal commands. 562 </para> 563 <para> 564 Once initialization is complete, host_set lock is acquired 565 and the qc is issued. 566 </para> 567 </listitem> 568 </varlistentry> 569 570 <varlistentry><term>SCSI commands</term> 571 <listitem> 572 <para> 573 All libata drivers use ata_scsi_queuecmd() as 574 hostt->queuecommand callback. scmds can either be simulated 575 or translated. No qc is involved in processing a simulated 576 scmd. The result is computed right away and the scmd is 577 completed. 578 </para> 579 <para> 580 For a translated scmd, ata_qc_new_init() is invoked to 581 allocate a qc and the scmd is translated into the qc. SCSI 582 midlayer's completion notification function pointer is stored 583 into qc->scsidone. 584 </para> 585 <para> 586 qc->complete_fn() callback is used for completion 587 notification. ATA commands use ata_scsi_qc_complete() while 588 ATAPI commands use atapi_qc_complete(). Both functions end up 589 calling qc->scsidone to notify upper layer when the qc is 590 finished. After translation is completed, the qc is issued 591 with ata_qc_issue(). 592 </para> 593 <para> 594 Note that SCSI midlayer invokes hostt->queuecommand while 595 holding host_set lock, so all above occur while holding 596 host_set lock. 597 </para> 598 </listitem> 599 </varlistentry> 600 601 </variablelist> 602 </sect1> 603 604 <sect1><title>How commands are processed</title> 605 <para> 606 Depending on which protocol and which controller are used, 607 commands are processed differently. For the purpose of 608 discussion, a controller which uses taskfile interface and all 609 standard callbacks is assumed. 610 </para> 611 <para> 612 Currently 6 ATA command protocols are used. They can be 613 sorted into the following four categories according to how 614 they are processed. 615 </para> 616 617 <variablelist> 618 <varlistentry><term>ATA NO DATA or DMA</term> 619 <listitem> 620 <para> 621 ATA_PROT_NODATA and ATA_PROT_DMA fall into this category. 622 These types of commands don't require any software 623 intervention once issued. Device will raise interrupt on 624 completion. 625 </para> 626 </listitem> 627 </varlistentry> 628 629 <varlistentry><term>ATA PIO</term> 630 <listitem> 631 <para> 632 ATA_PROT_PIO is in this category. libata currently 633 implements PIO with polling. ATA_NIEN bit is set to turn 634 off interrupt and pio_task on ata_wq performs polling and 635 IO. 636 </para> 637 </listitem> 638 </varlistentry> 639 640 <varlistentry><term>ATAPI NODATA or DMA</term> 641 <listitem> 642 <para> 643 ATA_PROT_ATAPI_NODATA and ATA_PROT_ATAPI_DMA are in this 644 category. packet_task is used to poll BSY bit after 645 issuing PACKET command. Once BSY is turned off by the 646 device, packet_task transfers CDB and hands off processing 647 to interrupt handler. 648 </para> 649 </listitem> 650 </varlistentry> 651 652 <varlistentry><term>ATAPI PIO</term> 653 <listitem> 654 <para> 655 ATA_PROT_ATAPI is in this category. ATA_NIEN bit is set 656 and, as in ATAPI NODATA or DMA, packet_task submits cdb. 657 However, after submitting cdb, further processing (data 658 transfer) is handed off to pio_task. 659 </para> 660 </listitem> 661 </varlistentry> 662 </variablelist> 663 </sect1> 664 665 <sect1><title>How commands are completed</title> 666 <para> 667 Once issued, all qc's are either completed with 668 ata_qc_complete() or time out. For commands which are handled 669 by interrupts, ata_host_intr() invokes ata_qc_complete(), and, 670 for PIO tasks, pio_task invokes ata_qc_complete(). In error 671 cases, packet_task may also complete commands. 672 </para> 673 <para> 674 ata_qc_complete() does the following. 675 </para> 676 677 <orderedlist> 678 679 <listitem> 680 <para> 681 DMA memory is unmapped. 682 </para> 683 </listitem> 684 685 <listitem> 686 <para> 687 ATA_QCFLAG_ACTIVE is clared from qc->flags. 688 </para> 689 </listitem> 690 691 <listitem> 692 <para> 693 qc->complete_fn() callback is invoked. If the return value of 694 the callback is not zero. Completion is short circuited and 695 ata_qc_complete() returns. 696 </para> 697 </listitem> 698 699 <listitem> 700 <para> 701 __ata_qc_complete() is called, which does 702 <orderedlist> 703 704 <listitem> 705 <para> 706 qc->flags is cleared to zero. 707 </para> 708 </listitem> 709 710 <listitem> 711 <para> 712 ap->active_tag and qc->tag are poisoned. 713 </para> 714 </listitem> 715 716 <listitem> 717 <para> 718 qc->waiting is claread & completed (in that order). 719 </para> 720 </listitem> 721 722 <listitem> 723 <para> 724 qc is deallocated by clearing appropriate bit in ap->qactive. 725 </para> 726 </listitem> 727 728 </orderedlist> 729 </para> 730 </listitem> 731 732 </orderedlist> 733 734 <para> 735 So, it basically notifies upper layer and deallocates qc. One 736 exception is short-circuit path in #3 which is used by 737 atapi_qc_complete(). 738 </para> 739 <para> 740 For all non-ATAPI commands, whether it fails or not, almost 741 the same code path is taken and very little error handling 742 takes place. A qc is completed with success status if it 743 succeeded, with failed status otherwise. 744 </para> 745 <para> 746 However, failed ATAPI commands require more handling as 747 REQUEST SENSE is needed to acquire sense data. If an ATAPI 748 command fails, ata_qc_complete() is invoked with error status, 749 which in turn invokes atapi_qc_complete() via 750 qc->complete_fn() callback. 751 </para> 752 <para> 753 This makes atapi_qc_complete() set scmd->result to 754 SAM_STAT_CHECK_CONDITION, complete the scmd and return 1. As 755 the sense data is empty but scmd->result is CHECK CONDITION, 756 SCSI midlayer will invoke EH for the scmd, and returning 1 757 makes ata_qc_complete() to return without deallocating the qc. 758 This leads us to ata_scsi_error() with partially completed qc. 759 </para> 760 761 </sect1> 762 763 <sect1><title>ata_scsi_error()</title> 764 <para> 765 ata_scsi_error() is the current transportt->eh_strategy_handler() 766 for libata. As discussed above, this will be entered in two 767 cases - timeout and ATAPI error completion. This function 768 calls low level libata driver's eng_timeout() callback, the 769 standard callback for which is ata_eng_timeout(). It checks 770 if a qc is active and calls ata_qc_timeout() on the qc if so. 771 Actual error handling occurs in ata_qc_timeout(). 772 </para> 773 <para> 774 If EH is invoked for timeout, ata_qc_timeout() stops BMDMA and 775 completes the qc. Note that as we're currently in EH, we 776 cannot call scsi_done. As described in SCSI EH doc, a 777 recovered scmd should be either retried with 778 scsi_queue_insert() or finished with scsi_finish_command(). 779 Here, we override qc->scsidone with scsi_finish_command() and 780 calls ata_qc_complete(). 781 </para> 782 <para> 783 If EH is invoked due to a failed ATAPI qc, the qc here is 784 completed but not deallocated. The purpose of this 785 half-completion is to use the qc as place holder to make EH 786 code reach this place. This is a bit hackish, but it works. 787 </para> 788 <para> 789 Once control reaches here, the qc is deallocated by invoking 790 __ata_qc_complete() explicitly. Then, internal qc for REQUEST 791 SENSE is issued. Once sense data is acquired, scmd is 792 finished by directly invoking scsi_finish_command() on the 793 scmd. Note that as we already have completed and deallocated 794 the qc which was associated with the scmd, we don't need 795 to/cannot call ata_qc_complete() again. 796 </para> 797 798 </sect1> 799 800 <sect1><title>Problems with the current EH</title> 801 802 <itemizedlist> 803 804 <listitem> 805 <para> 806 Error representation is too crude. Currently any and all 807 error conditions are represented with ATA STATUS and ERROR 808 registers. Errors which aren't ATA device errors are treated 809 as ATA device errors by setting ATA_ERR bit. Better error 810 descriptor which can properly represent ATA and other 811 errors/exceptions is needed. 812 </para> 813 </listitem> 814 815 <listitem> 816 <para> 817 When handling timeouts, no action is taken to make device 818 forget about the timed out command and ready for new commands. 819 </para> 820 </listitem> 821 822 <listitem> 823 <para> 824 EH handling via ata_scsi_error() is not properly protected 825 from usual command processing. On EH entrance, the device is 826 not in quiescent state. Timed out commands may succeed or 827 fail any time. pio_task and atapi_task may still be running. 828 </para> 829 </listitem> 830 831 <listitem> 832 <para> 833 Too weak error recovery. Devices / controllers causing HSM 834 mismatch errors and other errors quite often require reset to 835 return to known state. Also, advanced error handling is 836 necessary to support features like NCQ and hotplug. 837 </para> 838 </listitem> 839 840 <listitem> 841 <para> 842 ATA errors are directly handled in the interrupt handler and 843 PIO errors in pio_task. This is problematic for advanced 844 error handling for the following reasons. 845 </para> 846 <para> 847 First, advanced error handling often requires context and 848 internal qc execution. 849 </para> 850 <para> 851 Second, even a simple failure (say, CRC error) needs 852 information gathering and could trigger complex error handling 853 (say, resetting & reconfiguring). Having multiple code 854 paths to gather information, enter EH and trigger actions 855 makes life painful. 856 </para> 857 <para> 858 Third, scattered EH code makes implementing low level drivers 859 difficult. Low level drivers override libata callbacks. If 860 EH is scattered over several places, each affected callbacks 861 should perform its part of error handling. This can be error 862 prone and painful. 863 </para> 864 </listitem> 865 866 </itemizedlist> 867 </sect1> 868 </chapter> 869 870 <chapter id="libataExt"> 871 <title>libata Library</title> 872!Edrivers/ata/libata-core.c 873 </chapter> 874 875 <chapter id="libataInt"> 876 <title>libata Core Internals</title> 877!Idrivers/ata/libata-core.c 878 </chapter> 879 880 <chapter id="libataScsiInt"> 881 <title>libata SCSI translation/emulation</title> 882!Edrivers/ata/libata-scsi.c 883!Idrivers/ata/libata-scsi.c 884 </chapter> 885 886 <chapter id="ataExceptions"> 887 <title>ATA errors and exceptions</title> 888 889 <para> 890 This chapter tries to identify what error/exception conditions exist 891 for ATA/ATAPI devices and describe how they should be handled in 892 implementation-neutral way. 893 </para> 894 895 <para> 896 The term 'error' is used to describe conditions where either an 897 explicit error condition is reported from device or a command has 898 timed out. 899 </para> 900 901 <para> 902 The term 'exception' is either used to describe exceptional 903 conditions which are not errors (say, power or hotplug events), or 904 to describe both errors and non-error exceptional conditions. Where 905 explicit distinction between error and exception is necessary, the 906 term 'non-error exception' is used. 907 </para> 908 909 <sect1 id="excat"> 910 <title>Exception categories</title> 911 <para> 912 Exceptions are described primarily with respect to legacy 913 taskfile + bus master IDE interface. If a controller provides 914 other better mechanism for error reporting, mapping those into 915 categories described below shouldn't be difficult. 916 </para> 917 918 <para> 919 In the following sections, two recovery actions - reset and 920 reconfiguring transport - are mentioned. These are described 921 further in <xref linkend="exrec"/>. 922 </para> 923 924 <sect2 id="excatHSMviolation"> 925 <title>HSM violation</title> 926 <para> 927 This error is indicated when STATUS value doesn't match HSM 928 requirement during issuing or excution any ATA/ATAPI command. 929 </para> 930 931 <itemizedlist> 932 <title>Examples</title> 933 934 <listitem> 935 <para> 936 ATA_STATUS doesn't contain !BSY && DRDY && !DRQ while trying 937 to issue a command. 938 </para> 939 </listitem> 940 941 <listitem> 942 <para> 943 !BSY && !DRQ during PIO data transfer. 944 </para> 945 </listitem> 946 947 <listitem> 948 <para> 949 DRQ on command completion. 950 </para> 951 </listitem> 952 953 <listitem> 954 <para> 955 !BSY && ERR after CDB tranfer starts but before the 956 last byte of CDB is transferred. ATA/ATAPI standard states 957 that "The device shall not terminate the PACKET command 958 with an error before the last byte of the command packet has 959 been written" in the error outputs description of PACKET 960 command and the state diagram doesn't include such 961 transitions. 962 </para> 963 </listitem> 964 965 </itemizedlist> 966 967 <para> 968 In these cases, HSM is violated and not much information 969 regarding the error can be acquired from STATUS or ERROR 970 register. IOW, this error can be anything - driver bug, 971 faulty device, controller and/or cable. 972 </para> 973 974 <para> 975 As HSM is violated, reset is necessary to restore known state. 976 Reconfiguring transport for lower speed might be helpful too 977 as transmission errors sometimes cause this kind of errors. 978 </para> 979 </sect2> 980 981 <sect2 id="excatDevErr"> 982 <title>ATA/ATAPI device error (non-NCQ / non-CHECK CONDITION)</title> 983 984 <para> 985 These are errors detected and reported by ATA/ATAPI devices 986 indicating device problems. For this type of errors, STATUS 987 and ERROR register values are valid and describe error 988 condition. Note that some of ATA bus errors are detected by 989 ATA/ATAPI devices and reported using the same mechanism as 990 device errors. Those cases are described later in this 991 section. 992 </para> 993 994 <para> 995 For ATA commands, this type of errors are indicated by !BSY 996 && ERR during command execution and on completion. 997 </para> 998 999 <para>For ATAPI commands,</para> 1000
1001 <itemizedlist> 1002 1003 <listitem> 1004 <para> 1005 !BSY && ERR && ABRT right after issuing PACKET 1006 indicates that PACKET command is not supported and falls in 1007 this category. 1008 </para> 1009 </listitem> 1010 1011 <listitem> 1012 <para> 1013 !BSY && ERR(==CHK) && !ABRT after the last 1014 byte of CDB is transferred indicates CHECK CONDITION and 1015 doesn't fall in this category. 1016 </para> 1017 </listitem> 1018 1019 <listitem> 1020 <para> 1021 !BSY && ERR(==CHK) && ABRT after the last byte 1022 of CDB is transferred *probably* indicates CHECK CONDITION and 1023 doesn't fall in this category. 1024 </para> 1025 </listitem> 1026 1027 </itemizedlist> 1028 1029 <para> 1030 Of errors detected as above, the followings are not ATA/ATAPI 1031 device errors but ATA bus errors and should be handled 1032 according to <xref linkend="excatATAbusErr"/>. 1033 </para> 1034 1035 <variablelist> 1036 1037 <varlistentry> 1038 <term>CRC error during data transfer</term> 1039 <listitem> 1040 <para> 1041 This is indicated by ICRC bit in the ERROR register and 1042 means that corruption occurred during data transfer. Upto 1043 ATA/ATAPI-7, the standard specifies that this bit is only 1044 applicable to UDMA transfers but ATA/ATAPI-8 draft revision 1045 1f says that the bit may be applicable to multiword DMA and 1046 PIO. 1047 </para> 1048 </listitem> 1049 </varlistentry> 1050 1051 <varlistentry> 1052 <term>ABRT error during data transfer or on completion</term> 1053 <listitem> 1054 <para> 1055 Upto ATA/ATAPI-7, the standard specifies that ABRT could be 1056 set on ICRC errors and on cases where a device is not able 1057 to complete a command. Combined with the fact that MWDMA 1058 and PIO transfer errors aren't allowed to use ICRC bit upto 1059 ATA/ATAPI-7, it seems to imply that ABRT bit alone could 1060 indicate tranfer errors. 1061 </para> 1062 <para> 1063 However, ATA/ATAPI-8 draft revision 1f removes the part 1064 that ICRC errors can turn on ABRT. So, this is kind of 1065 gray area. Some heuristics are needed here. 1066 </para> 1067 </listitem> 1068 </varlistentry> 1069 1070 </variablelist> 1071 1072 <para> 1073 ATA/ATAPI device errors can be further categorized as follows. 1074 </para> 1075 1076 <variablelist> 1077 1078 <varlistentry> 1079 <term>Media errors</term> 1080 <listitem> 1081 <para> 1082 This is indicated by UNC bit in the ERROR register. ATA 1083 devices reports UNC error only after certain number of 1084 retries cannot recover the data, so there's nothing much 1085 else to do other than notifying upper layer. 1086 </para> 1087 <para> 1088 READ and WRITE commands report CHS or LBA of the first 1089 failed sector but ATA/ATAPI standard specifies that the 1090 amount of transferred data on error completion is 1091 indeterminate, so we cannot assume that sectors preceding 1092 the failed sector have been transferred and thus cannot 1093 complete those sectors successfully as SCSI does. 1094 </para> 1095 </listitem> 1096 </varlistentry> 1097 1098 <varlistentry> 1099 <term>Media changed / media change requested error</term> 1100 <listitem> 1101 <para> 1102 <<TODO: fill here>> 1103 </para> 1104 </listitem> 1105 </varlistentry> 1106 1107 <varlistentry><term>Address error</term> 1108 <listitem> 1109 <para> 1110 This is indicated by IDNF bit in the ERROR register. 1111 Report to upper layer. 1112 </para> 1113 </listitem> 1114 </varlistentry> 1115 1116 <varlistentry><term>Other errors</term> 1117 <listitem> 1118 <para> 1119 This can be invalid command or parameter indicated by ABRT 1120 ERROR bit or some other error condition. Note that ABRT 1121 bit can indicate a lot of things including ICRC and Address 1122 errors. Heuristics needed. 1123 </para> 1124 </listitem> 1125 </varlistentry> 1126 1127 </variablelist> 1128 1129 <para> 1130 Depending on commands, not all STATUS/ERROR bits are 1131 applicable. These non-applicable bits are marked with 1132 "na" in the output descriptions but upto ATA/ATAPI-7 1133 no definition of "na" can be found. However, 1134 ATA/ATAPI-8 draft revision 1f describes "N/A" as 1135 follows. 1136 </para> 1137 1138 <blockquote> 1139 <variablelist> 1140 <varlistentry><term>3.2.3.3a N/A</term> 1141 <listitem> 1142 <para> 1143 A keyword the indicates a field has no defined value in 1144 this standard and should not be checked by the host or 1145 device. N/A fields should be cleared to zero. 1146 </para> 1147 </listitem> 1148 </varlistentry> 1149 </variablelist> 1150 </blockquote> 1151 1152 <para> 1153 So, it seems reasonable to assume that "na" bits are 1154 cleared to zero by devices and thus need no explicit masking. 1155 </para> 1156 1157 </sect2> 1158 1159 <sect2 id="excatATAPIcc"> 1160 <title>ATAPI device CHECK CONDITION</title> 1161 1162 <para> 1163 ATAPI device CHECK CONDITION error is indicated by set CHK bit 1164 (ERR bit) in the STATUS register after the last byte of CDB is 1165 transferred for a PACKET command. For this kind of errors, 1166 sense data should be acquired to gather information regarding 1167 the errors. REQUEST SENSE packet command should be used to 1168 acquire sense data. 1169 </para> 1170 1171 <para> 1172 Once sense data is acquired, this type of errors can be 1173 handled similary to other SCSI errors. Note that sense data 1174 may indicate ATA bus error (e.g. Sense Key 04h HARDWARE ERROR 1175 && ASC/ASCQ 47h/00h SCSI PARITY ERROR). In such 1176 cases, the error should be considered as an ATA bus error and 1177 handled according to <xref linkend="excatATAbusErr"/>. 1178 </para> 1179 1180 </sect2> 1181 1182 <sect2 id="excatNCQerr"> 1183 <title>ATA device error (NCQ)</title> 1184 1185 <para> 1186 NCQ command error is indicated by cleared BSY and set ERR bit 1187 during NCQ command phase (one or more NCQ commands 1188 outstanding). Although STATUS and ERROR registers will 1189 contain valid values describing the error, READ LOG EXT is 1190 required to clear the error condition, determine which command 1191 has failed and acquire more information. 1192 </para> 1193 1194 <para> 1195 READ LOG EXT Log Page 10h reports which tag has failed and 1196 taskfile register values describing the error. With this 1197 information the failed command can be handled as a normal ATA 1198 command error as in <xref linkend="excatDevErr"/> and all 1199 other in-flight commands must be retried. Note that this 1200 retry should not be counted - it's likely that commands 1201 retried this way would have completed normally if it were not 1202 for the failed command. 1203 </para> 1204 1205 <para> 1206 Note that ATA bus errors can be reported as ATA device NCQ 1207 errors. This should be handled as described in <xref 1208 linkend="excatATAbusErr"/>. 1209 </para> 1210 1211 <para> 1212 If READ LOG EXT Log Page 10h fails or reports NQ, we're 1213 thoroughly screwed. This condition should be treated 1214 according to <xref linkend="excatHSMviolation"/>. 1215 </para> 1216 1217 </sect2> 1218 1219 <sect2 id="excatATAbusErr"> 1220 <title>ATA bus error</title> 1221 1222 <para> 1223 ATA bus error means that data corruption occurred during 1224 transmission over ATA bus (SATA or PATA). This type of errors 1225 can be indicated by 1226 </para> 1227 1228 <itemizedlist> 1229 1230 <listitem> 1231 <para> 1232 ICRC or ABRT error as described in <xref linkend="excatDevErr"/>. 1233 </para> 1234 </listitem> 1235 1236 <listitem> 1237 <para> 1238 Controller-specific error completion with error information 1239 indicating transmission error. 1240 </para> 1241 </listitem> 1242 1243 <listitem> 1244 <para> 1245 On some controllers, command timeout. In this case, there may 1246 be a mechanism to determine that the timeout is due to 1247 transmission error. 1248 </para> 1249 </listitem> 1250 1251 <listitem> 1252 <para> 1253 Unknown/random errors, timeouts and all sorts of weirdities. 1254 </para> 1255 </listitem> 1256 1257 </itemizedlist> 1258 1259 <para> 1260 As described above, transmission errors can cause wide variety 1261 of symptoms ranging from device ICRC error to random device 1262 lockup, and, for many cases, there is no way to tell if an 1263 error condition is due to transmission error or not; 1264 therefore, it's necessary to employ some kind of heuristic 1265 when dealing with errors and timeouts. For example, 1266 encountering repetitive ABRT errors for known supported 1267 command is likely to indicate ATA bus error. 1268 </para> 1269 1270 <para> 1271 Once it's determined that ATA bus errors have possibly 1272 occurred, lowering ATA bus transmission speed is one of 1273 actions which may alleviate the problem. See <xref 1274 linkend="exrecReconf"/> for more information. 1275 </para> 1276 1277 </sect2> 1278 1279 <sect2 id="excatPCIbusErr"> 1280 <title>PCI bus error</title> 1281 1282 <para> 1283 Data corruption or other failures during transmission over PCI 1284 (or other system bus). For standard BMDMA, this is indicated 1285 by Error bit in the BMDMA Status register. This type of 1286 errors must be logged as it indicates something is very wrong 1287 with the system. Resetting host controller is recommended. 1288 </para> 1289 1290 </sect2> 1291 1292 <sect2 id="excatLateCompletion"> 1293 <title>Late completion</title> 1294 1295 <para> 1296 This occurs when timeout occurs and the timeout handler finds 1297 out that the timed out command has completed successfully or 1298 with error. This is usually caused by lost interrupts. This 1299 type of errors must be logged. Resetting host controller is 1300 recommended. 1301 </para> 1302 1303 </sect2> 1304 1305 <sect2 id="excatUnknown"> 1306 <title>Unknown error (timeout)</title> 1307 1308 <para> 1309 This is when timeout occurs and the command is still 1310 processing or the host and device are in unknown state. When 1311 this occurs, HSM could be in any valid or invalid state. To 1312 bring the device to known state and make it forget about the 1313 timed out command, resetting is necessary. The timed out 1314 command may be retried. 1315 </para> 1316 1317 <para> 1318 Timeouts can also be caused by transmission errors. Refer to 1319 <xref linkend="excatATAbusErr"/> for more details. 1320 </para> 1321 1322 </sect2> 1323 1324 <sect2 id="excatHoplugPM"> 1325 <title>Hotplug and power management exceptions</title> 1326 1327 <para> 1328 <<TODO: fill here>> 1329 </para> 1330 1331 </sect2> 1332 1333 </sect1> 1334 1335 <sect1 id="exrec"> 1336 <title>EH recovery actions</title> 1337 1338 <para> 1339 This section discusses several important recovery actions. 1340 </para> 1341 1342 <sect2 id="exrecClr"> 1343 <title>Clearing error condition</title> 1344 1345 <para> 1346 Many controllers require its error registers to be cleared by 1347 error handler. Different controllers may have different 1348 requirements. 1349 </para> 1350 1351 <para> 1352 For SATA, it's strongly recommended to clear at least SError 1353 register during error handling. 1354 </para> 1355 </sect2> 1356 1357 <sect2 id="exrecRst"> 1358 <title>Reset</title> 1359 1360 <para> 1361 During EH, resetting is necessary in the following cases. 1362 </para> 1363 1364 <itemizedlist> 1365 1366 <listitem> 1367 <para> 1368 HSM is in unknown or invalid state 1369 </para> 1370 </listitem> 1371 1372 <listitem> 1373 <para> 1374 HBA is in unknown or invalid state 1375 </para> 1376 </listitem> 1377 1378 <listitem> 1379 <para> 1380 EH needs to make HBA/device forget about in-flight commands 1381 </para> 1382 </listitem> 1383 1384 <listitem> 1385 <para> 1386 HBA/device behaves weirdly 1387 </para> 1388 </listitem> 1389 1390 </itemizedlist> 1391 1392 <para> 1393 Resetting during EH might be a good idea regardless of error 1394 condition to improve EH robustness. Whether to reset both or 1395 either one of HBA and device depends on situation but the 1396 following scheme is recommended. 1397 </para> 1398 1399 <itemizedlist> 1400 1401 <listitem> 1402 <para> 1403 When it's known that HBA is in ready state but ATA/ATAPI 1404 device is in unknown state, reset only device. 1405 </para> 1406 </listitem> 1407 1408 <listitem> 1409 <para> 1410 If HBA is in unknown state, reset both HBA and device. 1411 </para> 1412 </listitem> 1413 1414 </itemizedlist> 1415 1416 <para> 1417 HBA resetting is implementation specific. For a controller 1418 complying to taskfile/BMDMA PCI IDE, stopping active DMA 1419 transaction may be sufficient iff BMDMA state is the only HBA 1420 context. But even mostly taskfile/BMDMA PCI IDE complying 1421 controllers may have implementation specific requirements and 1422 mechanism to reset themselves. This must be addressed by 1423 specific drivers. 1424 </para> 1425 1426 <para> 1427 OTOH, ATA/ATAPI standard describes in detail ways to reset 1428 ATA/ATAPI devices. 1429 </para> 1430 1431 <variablelist> 1432 1433 <varlistentry><term>PATA hardware reset</term> 1434 <listitem> 1435 <para> 1436 This is hardware initiated device reset signalled with 1437 asserted PATA RESET- signal. There is no standard way to 1438 initiate hardware reset from software although some 1439 hardware provides registers that allow driver to directly 1440 tweak the RESET- signal. 1441 </para> 1442 </listitem> 1443 </varlistentry> 1444 1445 <varlistentry><term>Software reset</term> 1446 <listitem> 1447 <para> 1448 This is achieved by turning CONTROL SRST bit on for at 1449 least 5us. Both PATA and SATA support it but, in case of 1450 SATA, this may require controller-specific support as the 1451 second Register FIS to clear SRST should be transmitted 1452 while BSY bit is still set. Note that on PATA, this resets 1453 both master and slave devices on a channel. 1454 </para> 1455 </listitem> 1456 </varlistentry> 1457 1458 <varlistentry><term>EXECUTE DEVICE DIAGNOSTIC command</term> 1459 <listitem> 1460 <para> 1461 Although ATA/ATAPI standard doesn't describe exactly, EDD 1462 implies some level of resetting, possibly similar level 1463 with software reset. Host-side EDD protocol can be handled 1464 with normal command processing and most SATA controllers 1465 should be able to handle EDD's just like other commands. 1466 As in software reset, EDD affects both devices on a PATA 1467 bus. 1468 </para> 1469 <para> 1470 Although EDD does reset devices, this doesn't suit error 1471 handling as EDD cannot be issued while BSY is set and it's 1472 unclear how it will act when device is in unknown/weird 1473 state. 1474 </para> 1475 </listitem> 1476 </varlistentry> 1477 1478 <varlistentry><term>ATAPI DEVICE RESET command</term> 1479 <listitem> 1480 <para> 1481 This is very similar to software reset except that reset 1482 can be restricted to the selected device without affecting 1483 the other device sharing the cable. 1484 </para> 1485 </listitem> 1486 </varlistentry> 1487 1488 <varlistentry><term>SATA phy reset</term> 1489 <listitem> 1490 <para> 1491 This is the preferred way of resetting a SATA device. In 1492 effect, it's identical to PATA hardware reset. Note that 1493 this can be done with the standard SCR Control register. 1494 As such, it's usually easier to implement than software 1495 reset. 1496 </para> 1497 </listitem> 1498 </varlistentry> 1499 1500 </variablelist> 1501 1502 <para> 1503 One more thing to consider when resetting devices is that 1504 resetting clears certain configuration parameters and they 1505 need to be set to their previous or newly adjusted values 1506 after reset. 1507 </para> 1508 1509 <para> 1510 Parameters affected are. 1511 </para> 1512 1513 <itemizedlist> 1514 1515 <listitem> 1516 <para> 1517 CHS set up with INITIALIZE DEVICE PARAMETERS (seldomly used) 1518 </para> 1519 </listitem> 1520 1521 <listitem> 1522 <para> 1523 Parameters set with SET FEATURES including transfer mode setting 1524 </para> 1525 </listitem> 1526 1527 <listitem> 1528 <para> 1529 Block count set with SET MULTIPLE MODE 1530 </para> 1531 </listitem> 1532 1533 <listitem> 1534 <para> 1535 Other parameters (SET MAX, MEDIA LOCK...) 1536 </para> 1537 </listitem> 1538 1539 </itemizedlist> 1540 1541 <para> 1542 ATA/ATAPI standard specifies that some parameters must be 1543 maintained across hardware or software reset, but doesn't 1544 strictly specify all of them. Always reconfiguring needed 1545 parameters after reset is required for robustness. Note that 1546 this also applies when resuming from deep sleep (power-off). 1547 </para> 1548 1549 <para> 1550 Also, ATA/ATAPI standard requires that IDENTIFY DEVICE / 1551 IDENTIFY PACKET DEVICE is issued after any configuration 1552 parameter is updated or a hardware reset and the result used 1553 for further operation. OS driver is required to implement 1554 revalidation mechanism to support this. 1555 </para> 1556 1557 </sect2> 1558 1559 <sect2 id="exrecReconf"> 1560 <title>Reconfigure transport</title> 1561 1562 <para> 1563 For both PATA and SATA, a lot of corners are cut for cheap 1564 connectors, cables or controllers and it's quite common to see 1565 high transmission error rate. This can be mitigated by 1566 lowering transmission speed. 1567 </para> 1568 1569 <para> 1570 The following is a possible scheme Jeff Garzik suggested. 1571 </para> 1572 1573 <blockquote> 1574 <para> 1575 If more than $N (3?) transmission errors happen in 15 minutes, 1576 </para> 1577 <itemizedlist> 1578 <listitem> 1579 <para> 1580 if SATA, decrease SATA PHY speed. if speed cannot be decreased, 1581 </para> 1582 </listitem> 1583 <listitem> 1584 <para> 1585 decrease UDMA xfer speed. if at UDMA0, switch to PIO4, 1586 </para> 1587 </listitem> 1588 <listitem> 1589 <para> 1590 decrease PIO xfer speed. if at PIO3, complain, but continue 1591 </para> 1592 </listitem> 1593 </itemizedlist> 1594 </blockquote> 1595 1596 </sect2> 1597 1598 </sect1> 1599 1600 </chapter> 1601 1602 <chapter id="PiixInt"> 1603 <title>ata_piix Internals</title> 1604!Idrivers/ata/ata_piix.c 1605 </chapter> 1606 1607 <chapter id="SILInt"> 1608 <title>sata_sil Internals</title> 1609!Idrivers/ata/sata_sil.c 1610 </chapter> 1611 1612 <chapter id="libataThanks"> 1613 <title>Thanks</title> 1614 <para> 1615 The bulk of the ATA knowledge comes thanks to long conversations with 1616 Andre Hedrick (www.linux-ide.org), and long hours pondering the ATA 1617 and SCSI specifications. 1618 </para> 1619 <para> 1620 Thanks to Alan Cox for pointing out similarities 1621 between SATA and SCSI, and in general for motivation to hack on 1622 libata. 1623 </para> 1624 <para> 1625 libata's device detection 1626 method, ata_pio_devchk, and in general all the early probing was 1627 based on extensive study of Hale Landis's probe/reset code in his 1628 ATADRVR driver (www.ata-atapi.com). 1629 </para> 1630 </chapter> 1631 1632</book> 1633