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Based on kernel version 3.13. Page generated on 2014-01-20 22:02 EST.

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