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1<?xml version="1.0" encoding="UTF-8"?>
2<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN"
3 "http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" []>
4
5<book id="libataDevGuide">
6 <bookinfo>
7 <title>libATA Developer's Guide</title>
8
9 <authorgroup>
10 <author>
11 <firstname>Jeff</firstname>
12 <surname>Garzik</surname>
13 </author>
14 </authorgroup>
15
16 <copyright>
17 <year>2003-2005</year>
18 <holder>Jeff Garzik</holder>
19 </copyright>
20
21 <legalnotice>
22 <para>
23 The contents of this file are subject to the Open
24 Software License version 1.1 that can be found at
25 <ulink url="http://www.opensource.org/licenses/osl-1.1.txt">http://www.opensource.org/licenses/osl-1.1.txt</ulink> and is included herein
26 by reference.
27 </para>
28
29 <para>
30 Alternatively, the contents of this file may be used under the terms
31 of the GNU General Public License version 2 (the "GPL") as distributed
32 in the kernel source COPYING file, in which case the provisions of
33 the GPL are applicable instead of the above. If you wish to allow
34 the use of your version of this file only under the terms of the
35 GPL and not to allow others to use your version of this file under
36 the OSL, indicate your decision by deleting the provisions above and
37 replace them with the notice and other provisions required by the GPL.
38 If you do not delete the provisions above, a recipient may use your
39 version of this file under either the OSL or the GPL.
40 </para>
41
42 </legalnotice>
43 </bookinfo>
44
45<toc></toc>
46
47 <chapter id="libataIntroduction">
48 <title>Introduction</title>
49 <para>
50 libATA is a library used inside the Linux kernel to support ATA host
51 controllers and devices. libATA provides an ATA driver API, class
52 transports for ATA and ATAPI devices, and SCSI<->ATA translation
53 for ATA devices according to the T10 SAT specification.
54 </para>
55 <para>
56 This Guide documents the libATA driver API, library functions, library
57 internals, and a couple sample ATA low-level drivers.
58 </para>
59 </chapter>
60
61 <chapter id="libataDriverApi">
62 <title>libata Driver API</title>
63 <para>
64 struct ata_port_operations is defined for every low-level libata
65 hardware driver, and it controls how the low-level driver
66 interfaces with the ATA and SCSI layers.
67 </para>
68 <para>
69 FIS-based drivers will hook into the system with ->qc_prep() and
70 ->qc_issue() high-level hooks. Hardware which behaves in a manner
71 similar to PCI IDE hardware may utilize several generic helpers,
72 defining at a bare minimum the bus I/O addresses of the ATA shadow
73 register blocks.
74 </para>
75 <sect1>
76 <title>struct ata_port_operations</title>
77
78 <sect2><title>Disable ATA port</title>
79 <programlisting>
80void (*port_disable) (struct ata_port *);
81 </programlisting>
82
83 <para>
84 Called from ata_bus_probe() and ata_bus_reset() error paths,
85 as well as when unregistering from the SCSI module (rmmod, hot
86 unplug).
87 This function should do whatever needs to be done to take the
88 port out of use. In most cases, ata_port_disable() can be used
89 as this hook.
90 </para>
91 <para>
92 Called from ata_bus_probe() on a failed probe.
93 Called from ata_bus_reset() on a failed bus reset.
94 Called from ata_scsi_release().
95 </para>
96
97 </sect2>
98
99 <sect2><title>Post-IDENTIFY device configuration</title>
100 <programlisting>
101void (*dev_config) (struct ata_port *, struct ata_device *);
102 </programlisting>
103
104 <para>
105 Called after IDENTIFY [PACKET] DEVICE is issued to each device
106 found. Typically used to apply device-specific fixups prior to
107 issue of SET FEATURES - XFER MODE, and prior to operation.
108 </para>
109 <para>
110 Called by ata_device_add() after ata_dev_identify() determines
111 a device is present.
112 </para>
113 <para>
114 This entry may be specified as NULL in ata_port_operations.
115 </para>
116
117 </sect2>
118
119 <sect2><title>Set PIO/DMA mode</title>
120 <programlisting>
121void (*set_piomode) (struct ata_port *, struct ata_device *);
122void (*set_dmamode) (struct ata_port *, struct ata_device *);
123void (*post_set_mode) (struct ata_port *ap);
124 </programlisting>
125
126 <para>
127 Hooks called prior to the issue of SET FEATURES - XFER MODE
128 command. dev->pio_mode is guaranteed to be valid when
129 ->set_piomode() is called, and dev->dma_mode is guaranteed to be
130 valid when ->set_dmamode() is called. ->post_set_mode() is
131 called unconditionally, after the SET FEATURES - XFER MODE
132 command completes successfully.
133 </para>
134
135 <para>
136 ->set_piomode() is always called (if present), but
137 ->set_dma_mode() is only called if DMA is possible.
138 </para>
139
140 </sect2>
141
142 <sect2><title>Taskfile read/write</title>
143 <programlisting>
144void (*tf_load) (struct ata_port *ap, struct ata_taskfile *tf);
145void (*tf_read) (struct ata_port *ap, struct ata_taskfile *tf);
146 </programlisting>
147
148 <para>
149 ->tf_load() is called to load the given taskfile into hardware
150 registers / DMA buffers. ->tf_read() is called to read the
151 hardware registers / DMA buffers, to obtain the current set of
152 taskfile register values.
153 Most drivers for taskfile-based hardware (PIO or MMIO) use
154 ata_tf_load() and ata_tf_read() for these hooks.
155 </para>
156
157 </sect2>
158
159 <sect2><title>ATA command execute</title>
160 <programlisting>
161void (*exec_command)(struct ata_port *ap, struct ata_taskfile *tf);
162 </programlisting>
163
164 <para>
165 causes an ATA command, previously loaded with
166 ->tf_load(), to be initiated in hardware.
167 Most drivers for taskfile-based hardware use ata_exec_command()
168 for this hook.
169 </para>
170
171 </sect2>
172
173 <sect2><title>Per-cmd ATAPI DMA capabilities filter</title>
174 <programlisting>
175int (*check_atapi_dma) (struct ata_queued_cmd *qc);
176 </programlisting>
177
178 <para>
179Allow low-level driver to filter ATA PACKET commands, returning a status
180indicating whether or not it is OK to use DMA for the supplied PACKET
181command.
182 </para>
183 <para>
184 This hook may be specified as NULL, in which case libata will
185 assume that atapi dma can be supported.
186 </para>
187
188 </sect2>
189
190 <sect2><title>Read specific ATA shadow registers</title>
191 <programlisting>
192u8 (*check_status)(struct ata_port *ap);
193u8 (*check_altstatus)(struct ata_port *ap);
194u8 (*check_err)(struct ata_port *ap);
195 </programlisting>
196
197 <para>
198 Reads the Status/AltStatus/Error ATA shadow register from
199 hardware. On some hardware, reading the Status register has
200 the side effect of clearing the interrupt condition.
201 Most drivers for taskfile-based hardware use
202 ata_check_status() for this hook.
203 </para>
204 <para>
205 Note that because this is called from ata_device_add(), at
206 least a dummy function that clears device interrupts must be
207 provided for all drivers, even if the controller doesn't
208 actually have a taskfile status register.
209 </para>
210
211 </sect2>
212
213 <sect2><title>Select ATA device on bus</title>
214 <programlisting>
215void (*dev_select)(struct ata_port *ap, unsigned int device);
216 </programlisting>
217
218 <para>
219 Issues the low-level hardware command(s) that causes one of N
220 hardware devices to be considered 'selected' (active and
221 available for use) on the ATA bus. This generally has no
222 meaning on FIS-based devices.
223 </para>
224 <para>
225 Most drivers for taskfile-based hardware use
226 ata_std_dev_select() for this hook. Controllers which do not
227 support second drives on a port (such as SATA contollers) will
228 use ata_noop_dev_select().
229 </para>
230
231 </sect2>
232
233 <sect2><title>Reset ATA bus</title>
234 <programlisting>
235void (*phy_reset) (struct ata_port *ap);
236 </programlisting>
237
238 <para>
239 The very first step in the probe phase. Actions vary depending
240 on the bus type, typically. After waking up the device and probing
241 for device presence (PATA and SATA), typically a soft reset
242 (SRST) will be performed. Drivers typically use the helper
243 functions ata_bus_reset() or sata_phy_reset() for this hook.
244 Many SATA drivers use sata_phy_reset() or call it from within
245 their own phy_reset() functions.
246 </para>
247
248 </sect2>
249
250 <sect2><title>Control PCI IDE BMDMA engine</title>
251 <programlisting>
252void (*bmdma_setup) (struct ata_queued_cmd *qc);
253void (*bmdma_start) (struct ata_queued_cmd *qc);
254void (*bmdma_stop) (struct ata_port *ap);
255u8 (*bmdma_status) (struct ata_port *ap);
256 </programlisting>
257
258 <para>
259When setting up an IDE BMDMA transaction, these hooks arm
260(->bmdma_setup), fire (->bmdma_start), and halt (->bmdma_stop)
261the hardware's DMA engine. ->bmdma_status is used to read the standard
262PCI IDE DMA Status register.
263 </para>
264
265 <para>
266These hooks are typically either no-ops, or simply not implemented, in
267FIS-based drivers.
268 </para>
269 <para>
270Most legacy IDE drivers use ata_bmdma_setup() for the bmdma_setup()
271hook. ata_bmdma_setup() will write the pointer to the PRD table to
272the IDE PRD Table Address register, enable DMA in the DMA Command
273register, and call exec_command() to begin the transfer.
274 </para>
275 <para>
276Most legacy IDE drivers use ata_bmdma_start() for the bmdma_start()
277hook. ata_bmdma_start() will write the ATA_DMA_START flag to the DMA
278Command register.
279 </para>
280 <para>
281Many legacy IDE drivers use ata_bmdma_stop() for the bmdma_stop()
282hook. ata_bmdma_stop() clears the ATA_DMA_START flag in the DMA
283command register.
284 </para>
285 <para>
286Many legacy IDE drivers use ata_bmdma_status() as the bmdma_status() hook.
287 </para>
288
289 </sect2>
290
291 <sect2><title>High-level taskfile hooks</title>
292 <programlisting>
293void (*qc_prep) (struct ata_queued_cmd *qc);
294int (*qc_issue) (struct ata_queued_cmd *qc);
295 </programlisting>
296
297 <para>
298 Higher-level hooks, these two hooks can potentially supercede
299 several of the above taskfile/DMA engine hooks. ->qc_prep is
300 called after the buffers have been DMA-mapped, and is typically
301 used to populate the hardware's DMA scatter-gather table.
302 Most drivers use the standard ata_qc_prep() helper function, but
303 more advanced drivers roll their own.
304 </para>
305 <para>
306 ->qc_issue is used to make a command active, once the hardware
307 and S/G tables have been prepared. IDE BMDMA drivers use the
308 helper function ata_qc_issue_prot() for taskfile protocol-based
309 dispatch. More advanced drivers implement their own ->qc_issue.
310 </para>
311 <para>
312 ata_qc_issue_prot() calls ->tf_load(), ->bmdma_setup(), and
313 ->bmdma_start() as necessary to initiate a transfer.
314 </para>
315
316 </sect2>
317
318 <sect2><title>Timeout (error) handling</title>
319 <programlisting>
320void (*eng_timeout) (struct ata_port *ap);
321 </programlisting>
322
323 <para>
324This is a high level error handling function, called from the
325error handling thread, when a command times out. Most newer
326hardware will implement its own error handling code here. IDE BMDMA
327drivers may use the helper function ata_eng_timeout().
328 </para>
329
330 </sect2>
331
332 <sect2><title>Hardware interrupt handling</title>
333 <programlisting>
334irqreturn_t (*irq_handler)(int, void *, struct pt_regs *);
335void (*irq_clear) (struct ata_port *);
336 </programlisting>
337
338 <para>
339 ->irq_handler is the interrupt handling routine registered with
340 the system, by libata. ->irq_clear is called during probe just
341 before the interrupt handler is registered, to be sure hardware
342 is quiet.
343 </para>
344 <para>
345 The second argument, dev_instance, should be cast to a pointer
346 to struct ata_host_set.
347 </para>
348 <para>
349 Most legacy IDE drivers use ata_interrupt() for the
350 irq_handler hook, which scans all ports in the host_set,
351 determines which queued command was active (if any), and calls
352 ata_host_intr(ap,qc).
353 </para>
354 <para>
355 Most legacy IDE drivers use ata_bmdma_irq_clear() for the
356 irq_clear() hook, which simply clears the interrupt and error
357 flags in the DMA status register.
358 </para>
359
360 </sect2>
361
362 <sect2><title>SATA phy read/write</title>
363 <programlisting>
364u32 (*scr_read) (struct ata_port *ap, unsigned int sc_reg);
365void (*scr_write) (struct ata_port *ap, unsigned int sc_reg,
366 u32 val);
367 </programlisting>
368
369 <para>
370 Read and write standard SATA phy registers. Currently only used
371 if ->phy_reset hook called the sata_phy_reset() helper function.
372 sc_reg is one of SCR_STATUS, SCR_CONTROL, SCR_ERROR, or SCR_ACTIVE.
373 </para>
374
375 </sect2>
376
377 <sect2><title>Init and shutdown</title>
378 <programlisting>
379int (*port_start) (struct ata_port *ap);
380void (*port_stop) (struct ata_port *ap);
381void (*host_stop) (struct ata_host_set *host_set);
382 </programlisting>
383
384 <para>
385 ->port_start() is called just after the data structures for each
386 port are initialized. Typically this is used to alloc per-port
387 DMA buffers / tables / rings, enable DMA engines, and similar
388 tasks. Some drivers also use this entry point as a chance to
389 allocate driver-private memory for ap->private_data.
390 </para>
391 <para>
392 Many drivers use ata_port_start() as this hook or call
393 it from their own port_start() hooks. ata_port_start()
394 allocates space for a legacy IDE PRD table and returns.
395 </para>
396 <para>
397 ->port_stop() is called after ->host_stop(). It's sole function
398 is to release DMA/memory resources, now that they are no longer
399 actively being used. Many drivers also free driver-private
400 data from port at this time.
401 </para>
402 <para>
403 Many drivers use ata_port_stop() as this hook, which frees the
404 PRD table.
405 </para>
406 <para>
407 ->host_stop() is called after all ->port_stop() calls
408have completed. The hook must finalize hardware shutdown, release DMA
409and other resources, etc.
410 This hook may be specified as NULL, in which case it is not called.
411 </para>
412
413 </sect2>
414
415 </sect1>
416 </chapter>
417
418 <chapter id="libataExt">
419 <title>libata Library</title>
420!Edrivers/scsi/libata-core.c
421 </chapter>
422
423 <chapter id="libataInt">
424 <title>libata Core Internals</title>
425!Idrivers/scsi/libata-core.c
426 </chapter>
427
428 <chapter id="libataScsiInt">
429 <title>libata SCSI translation/emulation</title>
430!Edrivers/scsi/libata-scsi.c
431!Idrivers/scsi/libata-scsi.c
432 </chapter>
433
434 <chapter id="PiixInt">
435 <title>ata_piix Internals</title>
436!Idrivers/scsi/ata_piix.c
437 </chapter>
438
439 <chapter id="SILInt">
440 <title>sata_sil Internals</title>
441!Idrivers/scsi/sata_sil.c
442 </chapter>
443
444 <chapter id="libataThanks">
445 <title>Thanks</title>
446 <para>
447 The bulk of the ATA knowledge comes thanks to long conversations with
448 Andre Hedrick (www.linux-ide.org), and long hours pondering the ATA
449 and SCSI specifications.
450 </para>
451 <para>
452 Thanks to Alan Cox for pointing out similarities
453 between SATA and SCSI, and in general for motivation to hack on
454 libata.
455 </para>
456 <para>
457 libata's device detection
458 method, ata_pio_devchk, and in general all the early probing was
459 based on extensive study of Hale Landis's probe/reset code in his
460 ATADRVR driver (www.ata-atapi.com).
461 </para>
462 </chapter>
463
464</book>