linux/Documentation/ide/ChangeLog.ide-tape.1995-2002
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   1/*
   2 * Ver 0.1   Nov  1 95   Pre-working code :-)
   3 * Ver 0.2   Nov 23 95   A short backup (few megabytes) and restore procedure
   4 *                        was successful ! (Using tar cvf ... on the block
   5 *                        device interface).
   6 *                       A longer backup resulted in major swapping, bad
   7 *                        overall Linux performance and eventually failed as
   8 *                        we received non serial read-ahead requests from the
   9 *                        buffer cache.
  10 * Ver 0.3   Nov 28 95   Long backups are now possible, thanks to the
  11 *                        character device interface. Linux's responsiveness
  12 *                        and performance doesn't seem to be much affected
  13 *                        from the background backup procedure.
  14 *                       Some general mtio.h magnetic tape operations are
  15 *                        now supported by our character device. As a result,
  16 *                        popular tape utilities are starting to work with
  17 *                        ide tapes :-)
  18 *                       The following configurations were tested:
  19 *                       1. An IDE ATAPI TAPE shares the same interface
  20 *                        and irq with an IDE ATAPI CDROM.
  21 *                       2. An IDE ATAPI TAPE shares the same interface
  22 *                        and irq with a normal IDE disk.
  23 *                        Both configurations seemed to work just fine !
  24 *                        However, to be on the safe side, it is meanwhile
  25 *                        recommended to give the IDE TAPE its own interface
  26 *                        and irq.
  27 *                       The one thing which needs to be done here is to
  28 *                        add a "request postpone" feature to ide.c,
  29 *                        so that we won't have to wait for the tape to finish
  30 *                        performing a long media access (DSC) request (such
  31 *                        as a rewind) before we can access the other device
  32 *                        on the same interface. This effect doesn't disturb
  33 *                        normal operation most of the time because read/write
  34 *                        requests are relatively fast, and once we are
  35 *                        performing one tape r/w request, a lot of requests
  36 *                        from the other device can be queued and ide.c will
  37 *                        service all of them after this single tape request.
  38 * Ver 1.0   Dec 11 95   Integrated into Linux 1.3.46 development tree.
  39 *                       On each read / write request, we now ask the drive
  40 *                        if we can transfer a constant number of bytes
  41 *                        (a parameter of the drive) only to its buffers,
  42 *                        without causing actual media access. If we can't,
  43 *                        we just wait until we can by polling the DSC bit.
  44 *                        This ensures that while we are not transferring
  45 *                        more bytes than the constant referred to above, the
  46 *                        interrupt latency will not become too high and
  47 *                        we won't cause an interrupt timeout, as happened
  48 *                        occasionally in the previous version.
  49 *                       While polling for DSC, the current request is
  50 *                        postponed and ide.c is free to handle requests from
  51 *                        the other device. This is handled transparently to
  52 *                        ide.c. The hwgroup locking method which was used
  53 *                        in the previous version was removed.
  54 *                       Use of new general features which are provided by
  55 *                        ide.c for use with atapi devices.
  56 *                        (Programming done by Mark Lord)
  57 *                       Few potential bug fixes (Again, suggested by Mark)
  58 *                       Single character device data transfers are now
  59 *                        not limited in size, as they were before.
  60 *                       We are asking the tape about its recommended
  61 *                        transfer unit and send a larger data transfer
  62 *                        as several transfers of the above size.
  63 *                        For best results, use an integral number of this
  64 *                        basic unit (which is shown during driver
  65 *                        initialization). I will soon add an ioctl to get
  66 *                        this important parameter.
  67 *                       Our data transfer buffer is allocated on startup,
  68 *                        rather than before each data transfer. This should
  69 *                        ensure that we will indeed have a data buffer.
  70 * Ver 1.1   Dec 14 95   Fixed random problems which occurred when the tape
  71 *                        shared an interface with another device.
  72 *                        (poll_for_dsc was a complete mess).
  73 *                       Removed some old (non-active) code which had
  74 *                        to do with supporting buffer cache originated
  75 *                        requests.
  76 *                       The block device interface can now be opened, so
  77 *                        that general ide driver features like the unmask
  78 *                        interrupts flag can be selected with an ioctl.
  79 *                        This is the only use of the block device interface.
  80 *                       New fast pipelined operation mode (currently only on
  81 *                        writes). When using the pipelined mode, the
  82 *                        throughput can potentially reach the maximum
  83 *                        tape supported throughput, regardless of the
  84 *                        user backup program. On my tape drive, it sometimes
  85 *                        boosted performance by a factor of 2. Pipelined
  86 *                        mode is enabled by default, but since it has a few
  87 *                        downfalls as well, you may want to disable it.
  88 *                        A short explanation of the pipelined operation mode
  89 *                        is available below.
  90 * Ver 1.2   Jan  1 96   Eliminated pipelined mode race condition.
  91 *                       Added pipeline read mode. As a result, restores
  92 *                        are now as fast as backups.
  93 *                       Optimized shared interface behavior. The new behavior
  94 *                        typically results in better IDE bus efficiency and
  95 *                        higher tape throughput.
  96 *                       Pre-calculation of the expected read/write request
  97 *                        service time, based on the tape's parameters. In
  98 *                        the pipelined operation mode, this allows us to
  99 *                        adjust our polling frequency to a much lower value,
 100 *                        and thus to dramatically reduce our load on Linux,
 101 *                        without any decrease in performance.
 102 *                       Implemented additional mtio.h operations.
 103 *                       The recommended user block size is returned by
 104 *                        the MTIOCGET ioctl.
 105 *                       Additional minor changes.
 106 * Ver 1.3   Feb  9 96   Fixed pipelined read mode bug which prevented the
 107 *                        use of some block sizes during a restore procedure.
 108 *                       The character device interface will now present a
 109 *                        continuous view of the media - any mix of block sizes
 110 *                        during a backup/restore procedure is supported. The
 111 *                        driver will buffer the requests internally and
 112 *                        convert them to the tape's recommended transfer
 113 *                        unit, making performance almost independent of the
 114 *                        chosen user block size.
 115 *                       Some improvements in error recovery.
 116 *                       By cooperating with ide-dma.c, bus mastering DMA can
 117 *                        now sometimes be used with IDE tape drives as well.
 118 *                        Bus mastering DMA has the potential to dramatically
 119 *                        reduce the CPU's overhead when accessing the device,
 120 *                        and can be enabled by using hdparm -d1 on the tape's
 121 *                        block device interface. For more info, read the
 122 *                        comments in ide-dma.c.
 123 * Ver 1.4   Mar 13 96   Fixed serialize support.
 124 * Ver 1.5   Apr 12 96   Fixed shared interface operation, broken in 1.3.85.
 125 *                       Fixed pipelined read mode inefficiency.
 126 *                       Fixed nasty null dereferencing bug.
 127 * Ver 1.6   Aug 16 96   Fixed FPU usage in the driver.
 128 *                       Fixed end of media bug.
 129 * Ver 1.7   Sep 10 96   Minor changes for the CONNER CTT8000-A model.
 130 * Ver 1.8   Sep 26 96   Attempt to find a better balance between good
 131 *                        interactive response and high system throughput.
 132 * Ver 1.9   Nov  5 96   Automatically cross encountered filemarks rather
 133 *                        than requiring an explicit FSF command.
 134 *                       Abort pending requests at end of media.
 135 *                       MTTELL was sometimes returning incorrect results.
 136 *                       Return the real block size in the MTIOCGET ioctl.
 137 *                       Some error recovery bug fixes.
 138 * Ver 1.10  Nov  5 96   Major reorganization.
 139 *                       Reduced CPU overhead a bit by eliminating internal
 140 *                        bounce buffers.
 141 *                       Added module support.
 142 *                       Added multiple tape drives support.
 143 *                       Added partition support.
 144 *                       Rewrote DSC handling.
 145 *                       Some portability fixes.
 146 *                       Removed ide-tape.h.
 147 *                       Additional minor changes.
 148 * Ver 1.11  Dec  2 96   Bug fix in previous DSC timeout handling.
 149 *                       Use ide_stall_queue() for DSC overlap.
 150 *                       Use the maximum speed rather than the current speed
 151 *                        to compute the request service time.
 152 * Ver 1.12  Dec  7 97   Fix random memory overwriting and/or last block data
 153 *                        corruption, which could occur if the total number
 154 *                        of bytes written to the tape was not an integral
 155 *                        number of tape blocks.
 156 *                       Add support for INTERRUPT DRQ devices.
 157 * Ver 1.13  Jan  2 98   Add "speed == 0" work-around for HP COLORADO 5GB
 158 * Ver 1.14  Dec 30 98   Partial fixes for the Sony/AIWA tape drives.
 159 *                       Replace cli()/sti() with hwgroup spinlocks.
 160 * Ver 1.15  Mar 25 99   Fix SMP race condition by replacing hwgroup
 161 *                        spinlock with private per-tape spinlock.
 162 * Ver 1.16  Sep  1 99   Add OnStream tape support.
 163 *                       Abort read pipeline on EOD.
 164 *                       Wait for the tape to become ready in case it returns
 165 *                        "in the process of becoming ready" on open().
 166 *                       Fix zero padding of the last written block in
 167 *                        case the tape block size is larger than PAGE_SIZE.
 168 *                       Decrease the default disconnection time to tn.
 169 * Ver 1.16e Oct  3 99   Minor fixes.
 170 * Ver 1.16e1 Oct 13 99  Patches by Arnold Niessen,
 171 *                          niessen@iae.nl / arnold.niessen@philips.com
 172 *                   GO-1)  Undefined code in idetape_read_position
 173 *                              according to Gadi's email
 174 *                   AJN-1) Minor fix asc == 11 should be asc == 0x11
 175 *                               in idetape_issue_packet_command (did effect
 176 *                               debugging output only)
 177 *                   AJN-2) Added more debugging output, and
 178 *                              added ide-tape: where missing. I would also
 179 *                              like to add tape->name where possible
 180 *                   AJN-3) Added different debug_level's
 181 *                              via /proc/ide/hdc/settings
 182 *                              "debug_level" determines amount of debugging output;
 183 *                              can be changed using /proc/ide/hdx/settings
 184 *                              0 : almost no debugging output
 185 *                              1 : 0+output errors only
 186 *                              2 : 1+output all sensekey/asc
 187 *                              3 : 2+follow all chrdev related procedures
 188 *                              4 : 3+follow all procedures
 189 *                              5 : 4+include pc_stack rq_stack info
 190 *                              6 : 5+USE_COUNT updates
 191 *                   AJN-4) Fixed timeout for retension in idetape_queue_pc_tail
 192 *                              from 5 to 10 minutes
 193 *                   AJN-5) Changed maximum number of blocks to skip when
 194 *                              reading tapes with multiple consecutive write
 195 *                              errors from 100 to 1000 in idetape_get_logical_blk
 196 *                   Proposed changes to code:
 197 *                   1) output "logical_blk_num" via /proc
 198 *                   2) output "current_operation" via /proc
 199 *                   3) Either solve or document the fact that `mt rewind' is
 200 *                      required after reading from /dev/nhtx to be
 201 *                      able to rmmod the idetape module;
 202 *                      Also, sometimes an application finishes but the
 203 *                      device remains `busy' for some time. Same cause ?
 204 *                   Proposed changes to release-notes:
 205 *                   4) write a simple `quickstart' section in the
 206 *                      release notes; I volunteer if you don't want to
 207 *                   5) include a pointer to video4linux in the doc
 208 *                      to stimulate video applications
 209 *                   6) release notes lines 331 and 362: explain what happens
 210 *                      if the application data rate is higher than 1100 KB/s;
 211 *                      similar approach to lower-than-500 kB/s ?
 212 *                   7) 6.6 Comparison; wouldn't it be better to allow different
 213 *                      strategies for read and write ?
 214 *                      Wouldn't it be better to control the tape buffer
 215 *                      contents instead of the bandwidth ?
 216 *                   8) line 536: replace will by would (if I understand
 217 *                      this section correctly, a hypothetical and unwanted situation
 218 *                       is being described)
 219 * Ver 1.16f Dec 15 99   Change place of the secondary OnStream header frames.
 220 * Ver 1.17  Nov 2000 / Jan 2001  Marcel Mol, marcel@mesa.nl
 221 *                      - Add idetape_onstream_mode_sense_tape_parameter_page
 222 *                        function to get tape capacity in frames: tape->capacity.
 223 *                      - Add support for DI-50 drives( or any DI- drive).
 224 *                      - 'workaround' for read error/blank block around block 3000.
 225 *                      - Implement Early warning for end of media for Onstream.
 226 *                      - Cosmetic code changes for readability.
 227 *                      - Idetape_position_tape should not use SKIP bit during
 228 *                        Onstream read recovery.
 229 *                      - Add capacity, logical_blk_num and first/last_frame_position
 230 *                        to /proc/ide/hd?/settings.
 231 *                      - Module use count was gone in the Linux 2.4 driver.
 232 * Ver 1.17a Apr 2001 Willem Riede osst@riede.org
 233 *                      - Get drive's actual block size from mode sense block descriptor
 234 *                      - Limit size of pipeline
 235 * Ver 1.17b Oct 2002   Alan Stern <stern@rowland.harvard.edu>
 236 *                      Changed IDETAPE_MIN_PIPELINE_STAGES to 1 and actually used
 237 *                       it in the code!
 238 *                      Actually removed aborted stages in idetape_abort_pipeline
 239 *                       instead of just changing the command code.
 240 *                      Made the transfer byte count for Request Sense equal to the
 241 *                       actual length of the data transfer.
 242 *                      Changed handling of partial data transfers: they do not
 243 *                       cause DMA errors.
 244 *                      Moved initiation of DMA transfers to the correct place.
 245 *                      Removed reference to unallocated memory.
 246 *                      Made __idetape_discard_read_pipeline return the number of
 247 *                       sectors skipped, not the number of stages.
 248 *                      Replaced errant kfree() calls with __idetape_kfree_stage().
 249 *                      Fixed off-by-one error in testing the pipeline length.
 250 *                      Fixed handling of filemarks in the read pipeline.
 251 *                      Small code optimization for MTBSF and MTBSFM ioctls.
 252 *                      Don't try to unlock the door during device close if is
 253 *                       already unlocked!
 254 *                      Cosmetic fixes to miscellaneous debugging output messages.
 255 *                      Set the minimum /proc/ide/hd?/settings values for "pipeline",
 256 *                       "pipeline_min", and "pipeline_max" to 1.
 257 */
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