kernel packet parsing bugfixes, some htable changes
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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" []>
5 <book id="libataDevGuide">
6 <bookinfo>
7 <title>libATA Developer's Guide</title>
9 <authorgroup>
10 <author>
11 <firstname>Jeff</firstname>
12 <surname>Garzik</surname>
13 </author>
14 </authorgroup>
16 <copyright>
17 <year>2003-2006</year>
18 <holder>Jeff Garzik</holder>
19 </copyright>
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>
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>
42 </legalnotice>
43 </bookinfo>
45 <toc></toc>
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>
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>
78 <sect2><title>Disable ATA port</title>
79 <programlisting>
80 void (*port_disable) (struct ata_port *);
81 </programlisting>
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>
97 </sect2>
99 <sect2><title>Post-IDENTIFY device configuration</title>
100 <programlisting>
101 void (*dev_config) (struct ata_port *, struct ata_device *);
102 </programlisting>
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>
117 </sect2>
119 <sect2><title>Set PIO/DMA mode</title>
120 <programlisting>
121 void (*set_piomode) (struct ata_port *, struct ata_device *);
122 void (*set_dmamode) (struct ata_port *, struct ata_device *);
123 void (*post_set_mode) (struct ata_port *);
124 unsigned int (*mode_filter) (struct ata_port *, struct ata_device *, unsigned int);
125 </programlisting>
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>
148 <para>
149 ->set_piomode() is always called (if present), but
150 ->set_dma_mode() is only called if DMA is possible.
151 </para>
153 </sect2>
155 <sect2><title>Taskfile read/write</title>
156 <programlisting>
157 void (*tf_load) (struct ata_port *ap, struct ata_taskfile *tf);
158 void (*tf_read) (struct ata_port *ap, struct ata_taskfile *tf);
159 </programlisting>
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>
170 </sect2>
172 <sect2><title>PIO data read/write</title>
173 <programlisting>
174 void (*data_xfer) (struct ata_device *, unsigned char *, unsigned int, int);
175 </programlisting>
177 <para>
178 All bmdma-style drivers must implement this hook. This is the low-level
179 operation that actually copies the data bytes during a PIO data
180 transfer.
181 Typically the driver
182 will choose one of ata_pio_data_xfer_noirq(), ata_pio_data_xfer(), or
183 ata_mmio_data_xfer().
184 </para>
186 </sect2>
188 <sect2><title>ATA command execute</title>
189 <programlisting>
190 void (*exec_command)(struct ata_port *ap, struct ata_taskfile *tf);
191 </programlisting>
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>
200 </sect2>
202 <sect2><title>Per-cmd ATAPI DMA capabilities filter</title>
203 <programlisting>
204 int (*check_atapi_dma) (struct ata_queued_cmd *qc);
205 </programlisting>
207 <para>
208 Allow low-level driver to filter ATA PACKET commands, returning a status
209 indicating whether or not it is OK to use DMA for the supplied PACKET
210 command.
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>
217 </sect2>
219 <sect2><title>Read specific ATA shadow registers</title>
220 <programlisting>
221 u8 (*check_status)(struct ata_port *ap);
222 u8 (*check_altstatus)(struct ata_port *ap);
223 </programlisting>
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>
239 </sect2>
241 <sect2><title>Select ATA device on bus</title>
242 <programlisting>
243 void (*dev_select)(struct ata_port *ap, unsigned int device);
244 </programlisting>
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>
259 </sect2>
261 <sect2><title>Private tuning method</title>
262 <programlisting>
263 void (*set_mode) (struct ata_port *ap);
264 </programlisting>
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>
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>
285 </sect2>
287 <sect2><title>Control PCI IDE BMDMA engine</title>
288 <programlisting>
289 void (*bmdma_setup) (struct ata_queued_cmd *qc);
290 void (*bmdma_start) (struct ata_queued_cmd *qc);
291 void (*bmdma_stop) (struct ata_port *ap);
292 u8 (*bmdma_status) (struct ata_port *ap);
293 </programlisting>
295 <para>
296 When setting up an IDE BMDMA transaction, these hooks arm
297 (->bmdma_setup), fire (->bmdma_start), and halt (->bmdma_stop)
298 the hardware's DMA engine. ->bmdma_status is used to read the standard
299 PCI IDE DMA Status register.
300 </para>
302 <para>
303 These hooks are typically either no-ops, or simply not implemented, in
304 FIS-based drivers.
305 </para>
306 <para>
307 Most legacy IDE drivers use ata_bmdma_setup() for the bmdma_setup()
308 hook. ata_bmdma_setup() will write the pointer to the PRD table to
309 the IDE PRD Table Address register, enable DMA in the DMA Command
310 register, and call exec_command() to begin the transfer.
311 </para>
312 <para>
313 Most legacy IDE drivers use ata_bmdma_start() for the bmdma_start()
314 hook. ata_bmdma_start() will write the ATA_DMA_START flag to the DMA
315 Command register.
316 </para>
317 <para>
318 Many legacy IDE drivers use ata_bmdma_stop() for the bmdma_stop()
319 hook. ata_bmdma_stop() clears the ATA_DMA_START flag in the DMA
320 command register.
321 </para>
322 <para>
323 Many legacy IDE drivers use ata_bmdma_status() as the bmdma_status() hook.
324 </para>
326 </sect2>
328 <sect2><title>High-level taskfile hooks</title>
329 <programlisting>
330 void (*qc_prep) (struct ata_queued_cmd *qc);
331 int (*qc_issue) (struct ata_queued_cmd *qc);
332 </programlisting>
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>
353 </sect2>
355 <sect2><title>Exception and probe handling (EH)</title>
356 <programlisting>
357 void (*eng_timeout) (struct ata_port *ap);
358 void (*phy_reset) (struct ata_port *ap);
359 </programlisting>
361 <para>
362 Deprecated. Use ->error_handler() instead.
363 </para>
365 <programlisting>
366 void (*freeze) (struct ata_port *ap);
367 void (*thaw) (struct ata_port *ap);
368 </programlisting>
370 <para>
371 ata_port_freeze() is called when HSM violations or some other
372 condition disrupts normal operation of the port. A frozen port
373 is not allowed to perform any operation until the port is
374 thawed, which usually follows a successful reset.
375 </para>
377 <para>
378 The optional ->freeze() callback can be used for freezing the port
379 hardware-wise (e.g. mask interrupt and stop DMA engine). If a
380 port cannot be frozen hardware-wise, the interrupt handler
381 must ack and clear interrupts unconditionally while the port
382 is frozen.
383 </para>
384 <para>
385 The optional ->thaw() callback is called to perform the opposite of ->freeze():
386 prepare the port for normal operation once again. Unmask interrupts,
387 start DMA engine, etc.
388 </para>
390 <programlisting>
391 void (*error_handler) (struct ata_port *ap);
392 </programlisting>
394 <para>
395 ->error_handler() is a driver's hook into probe, hotplug, and recovery
396 and other exceptional conditions. The primary responsibility of an
397 implementation is to call ata_do_eh() or ata_bmdma_drive_eh() with a set
398 of EH hooks as arguments:
399 </para>
401 <para>
402 'prereset' hook (may be NULL) is called during an EH reset, before any other actions
403 are taken.
404 </para>
406 <para>
407 'postreset' hook (may be NULL) is called after the EH reset is performed. Based on
408 existing conditions, severity of the problem, and hardware capabilities,
409 </para>
411 <para>
412 Either 'softreset' (may be NULL) or 'hardreset' (may be NULL) will be
413 called to perform the low-level EH reset.
414 </para>
416 <programlisting>
417 void (*post_internal_cmd) (struct ata_queued_cmd *qc);
418 </programlisting>
420 <para>
421 Perform any hardware-specific actions necessary to finish processing
422 after executing a probe-time or EH-time command via ata_exec_internal().
423 </para>
425 </sect2>
427 <sect2><title>Hardware interrupt handling</title>
428 <programlisting>
429 irqreturn_t (*irq_handler)(int, void *, struct pt_regs *);
430 void (*irq_clear) (struct ata_port *);
431 </programlisting>
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>
455 </sect2>
457 <sect2><title>SATA phy read/write</title>
458 <programlisting>
459 int (*scr_read) (struct ata_port *ap, unsigned int sc_reg,
460 u32 *val);
461 int (*scr_write) (struct ata_port *ap, unsigned int sc_reg,
462 u32 val);
463 </programlisting>
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>
471 </sect2>
473 <sect2><title>Init and shutdown</title>
474 <programlisting>
475 int (*port_start) (struct ata_port *ap);
476 void (*port_stop) (struct ata_port *ap);
477 void (*host_stop) (struct ata_host_set *host_set);
478 </programlisting>
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
504 have completed. The hook must finalize hardware shutdown, release DMA
505 and other resources, etc.
506 This hook may be specified as NULL, in which case it is not called.
507 </para>
509 </sect2>
511 </sect1>
512 </chapter>
514 <chapter id="libataEH">
515 <title>Error handling</title>
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>
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>
540 <sect1><title>How commands are issued</title>
542 <variablelist>
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>
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>
601 </variablelist>
602 </sect1>
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>
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>
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
636 </para>
637 </listitem>
638 </varlistentry>
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>
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>
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>
677 <orderedlist>
679 <listitem>
680 <para>
681 DMA memory is unmapped.
682 </para>
683 </listitem>
685 <listitem>
686 <para>
687 ATA_QCFLAG_ACTIVE is clared from qc->flags.
688 </para>
689 </listitem>
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>
699 <listitem>
700 <para>
701 __ata_qc_complete() is called, which does
702 <orderedlist>
704 <listitem>
705 <para>
706 qc->flags is cleared to zero.
707 </para>
708 </listitem>
710 <listitem>
711 <para>
712 ap->active_tag and qc->tag are poisoned.
713 </para>
714 </listitem>
716 <listitem>
717 <para>
718 qc->waiting is claread &amp; completed (in that order).
719 </para>
720 </listitem>
722 <listitem>
723 <para>
724 qc is deallocated by clearing appropriate bit in ap->qactive.
725 </para>
726 </listitem>
728 </orderedlist>
729 </para>
730 </listitem>
732 </orderedlist>
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>
761 </sect1>
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>
798 </sect1>
800 <sect1><title>Problems with the current EH</title>
802 <itemizedlist>
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>
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>
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>
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>
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 &amp; 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>
866 </itemizedlist>
867 </sect1>
868 </chapter>
870 <chapter id="libataExt">
871 <title>libata Library</title>
872 !Edrivers/ata/libata-core.c
873 </chapter>
875 <chapter id="libataInt">
876 <title>libata Core Internals</title>
877 !Idrivers/ata/libata-core.c
878 </chapter>
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>
886 <chapter id="ataExceptions">
887 <title>ATA errors and exceptions</title>
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>
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>
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>
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>
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>
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>
931 <itemizedlist>
932 <title>Examples</title>
934 <listitem>
935 <para>
936 ATA_STATUS doesn't contain !BSY &amp;&amp; DRDY &amp;&amp; !DRQ while trying
937 to issue a command.
938 </para>
939 </listitem>
941 <listitem>
942 <para>
943 !BSY &amp;&amp; !DRQ during PIO data transfer.
944 </para>
945 </listitem>
947 <listitem>
948 <para>
949 DRQ on command completion.
950 </para>
951 </listitem>
953 <listitem>
954 <para>
955 !BSY &amp;&amp; ERR after CDB tranfer starts but before the
956 last byte of CDB is transferred. ATA/ATAPI standard states
957 that &quot;The device shall not terminate the PACKET command
958 with an error before the last byte of the command packet has
959 been written&quot; in the error outputs description of PACKET
960 command and the state diagram doesn't include such
961 transitions.
962 </para>
963 </listitem>
965 </itemizedlist>
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>
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>
981 <sect2 id="excatDevErr">
982 <title>ATA/ATAPI device error (non-NCQ / non-CHECK CONDITION)</title>
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>
994 <para>
995 For ATA commands, this type of errors are indicated by !BSY
996 &amp;&amp; ERR during command execution and on completion.
997 </para>
999 <para>For ATAPI commands,</para>
1001 <itemizedlist>
1003 <listitem>
1004 <para>
1005 !BSY &amp;&amp; ERR &amp;&amp; ABRT right after issuing PACKET
1006 indicates that PACKET command is not supported and falls in
1007 this category.
1008 </para>
1009 </listitem>
1011 <listitem>
1012 <para>
1013 !BSY &amp;&amp; ERR(==CHK) &amp;&amp; !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>
1019 <listitem>
1020 <para>
1021 !BSY &amp;&amp; ERR(==CHK) &amp;&amp; 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>
1027 </itemizedlist>
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>
1035 <variablelist>
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>
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>
1070 </variablelist>
1072 <para>
1073 ATA/ATAPI device errors can be further categorized as follows.
1074 </para>
1076 <variablelist>
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>
1098 <varlistentry>
1099 <term>Media changed / media change requested error</term>
1100 <listitem>
1101 <para>
1102 &lt;&lt;TODO: fill here&gt;&gt;
1103 </para>
1104 </listitem>
1105 </varlistentry>
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>
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>
1127 </variablelist>
1129 <para>
1130 Depending on commands, not all STATUS/ERROR bits are
1131 applicable. These non-applicable bits are marked with
1132 &quot;na&quot; in the output descriptions but upto ATA/ATAPI-7
1133 no definition of &quot;na&quot; can be found. However,
1134 ATA/ATAPI-8 draft revision 1f describes &quot;N/A&quot; as
1135 follows.
1136 </para>
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>
1152 <para>
1153 So, it seems reasonable to assume that &quot;na&quot; bits are
1154 cleared to zero by devices and thus need no explicit masking.
1155 </para>
1157 </sect2>
1159 <sect2 id="excatATAPIcc">
1160 <title>ATAPI device CHECK CONDITION</title>
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>
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 &amp;&amp; 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>
1180 </sect2>
1182 <sect2 id="excatNCQerr">
1183 <title>ATA device error (NCQ)</title>
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>
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>
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>
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>
1217 </sect2>
1219 <sect2 id="excatATAbusErr">
1220 <title>ATA bus error</title>
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>
1228 <itemizedlist>
1230 <listitem>
1231 <para>
1232 ICRC or ABRT error as described in <xref linkend="excatDevErr"/>.
1233 </para>
1234 </listitem>
1236 <listitem>
1237 <para>
1238 Controller-specific error completion with error information
1239 indicating transmission error.
1240 </para>
1241 </listitem>
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>
1251 <listitem>
1252 <para>
1253 Unknown/random errors, timeouts and all sorts of weirdities.
1254 </para>
1255 </listitem>
1257 </itemizedlist>
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>
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>
1277 </sect2>
1279 <sect2 id="excatPCIbusErr">
1280 <title>PCI bus error</title>
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>
1290 </sect2>
1292 <sect2 id="excatLateCompletion">
1293 <title>Late completion</title>
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>
1303 </sect2>
1305 <sect2 id="excatUnknown">
1306 <title>Unknown error (timeout)</title>
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>
1317 <para>
1318 Timeouts can also be caused by transmission errors. Refer to
1319 <xref linkend="excatATAbusErr"/> for more details.
1320 </para>
1322 </sect2>
1324 <sect2 id="excatHoplugPM">
1325 <title>Hotplug and power management exceptions</title>
1327 <para>
1328 &lt;&lt;TODO: fill here&gt;&gt;
1329 </para>
1331 </sect2>
1333 </sect1>
1335 <sect1 id="exrec">
1336 <title>EH recovery actions</title>
1338 <para>
1339 This section discusses several important recovery actions.
1340 </para>
1342 <sect2 id="exrecClr">
1343 <title>Clearing error condition</title>
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>
1351 <para>
1352 For SATA, it's strongly recommended to clear at least SError
1353 register during error handling.
1354 </para>
1355 </sect2>
1357 <sect2 id="exrecRst">
1358 <title>Reset</title>
1360 <para>
1361 During EH, resetting is necessary in the following cases.
1362 </para>
1364 <itemizedlist>
1366 <listitem>
1367 <para>
1368 HSM is in unknown or invalid state
1369 </para>
1370 </listitem>
1372 <listitem>
1373 <para>
1374 HBA is in unknown or invalid state
1375 </para>
1376 </listitem>
1378 <listitem>
1379 <para>
1380 EH needs to make HBA/device forget about in-flight commands
1381 </para>
1382 </listitem>
1384 <listitem>
1385 <para>
1386 HBA/device behaves weirdly
1387 </para>
1388 </listitem>
1390 </itemizedlist>
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>
1399 <itemizedlist>
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>
1408 <listitem>
1409 <para>
1410 If HBA is in unknown state, reset both HBA and device.
1411 </para>
1412 </listitem>
1414 </itemizedlist>
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>
1426 <para>
1427 OTOH, ATA/ATAPI standard describes in detail ways to reset
1428 ATA/ATAPI devices.
1429 </para>
1431 <variablelist>
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>
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>
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>
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>
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>
1500 </variablelist>
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>
1509 <para>
1510 Parameters affected are.
1511 </para>
1513 <itemizedlist>
1515 <listitem>
1516 <para>
1517 CHS set up with INITIALIZE DEVICE PARAMETERS (seldomly used)
1518 </para>
1519 </listitem>
1521 <listitem>
1522 <para>
1523 Parameters set with SET FEATURES including transfer mode setting
1524 </para>
1525 </listitem>
1527 <listitem>
1528 <para>
1529 Block count set with SET MULTIPLE MODE
1530 </para>
1531 </listitem>
1533 <listitem>
1534 <para>
1535 Other parameters (SET MAX, MEDIA LOCK...)
1536 </para>
1537 </listitem>
1539 </itemizedlist>
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>
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>
1557 </sect2>
1559 <sect2 id="exrecReconf">
1560 <title>Reconfigure transport</title>
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>
1569 <para>
1570 The following is a possible scheme Jeff Garzik suggested.
1571 </para>
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>
1596 </sect2>
1598 </sect1>
1600 </chapter>
1602 <chapter id="PiixInt">
1603 <title>ata_piix Internals</title>
1604 !Idrivers/ata/ata_piix.c
1605 </chapter>
1607 <chapter id="SILInt">
1608 <title>sata_sil Internals</title>
1609 !Idrivers/ata/sata_sil.c
1610 </chapter>
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>
1632 </book>