<?xml version="1.0" encoding="UTF-8"?><!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN"	"http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" []> <book id="libataDevGuide"> <bookinfo>  <title>libATA Developer's Guide</title>    <authorgroup>   <author>    <firstname>Jeff</firstname>    <surname>Garzik</surname>   </author>  </authorgroup>   <copyright>   <year>2003-2005</year>   <holder>Jeff Garzik</holder>  </copyright>   <legalnotice>   <para>   The contents of this file are subject to the Open   Software License version 1.1 that can be found at   <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   by reference.   </para>    <para>   Alternatively, the contents of this file may be used under the terms   of the GNU General Public License version 2 (the "GPL") as distributed   in the kernel source COPYING file, in which case the provisions of   the GPL are applicable instead of the above.  If you wish to allow   the use of your version of this file only under the terms of the   GPL and not to allow others to use your version of this file under   the OSL, indicate your decision by deleting the provisions above and   replace them with the notice and other provisions required by the GPL.   If you do not delete the provisions above, a recipient may use your   version of this file under either the OSL or the GPL.   </para>   </legalnotice> </bookinfo> <toc></toc>   <chapter id="libataIntroduction">     <title>Introduction</title>  <para>  libATA is a library used inside the Linux kernel to support ATA host  controllers and devices.  libATA provides an ATA driver API, class  transports for ATA and ATAPI devices, and SCSI&lt;-&gt;ATA translation  for ATA devices according to the T10 SAT specification.  </para>  <para>  This Guide documents the libATA driver API, library functions, library  internals, and a couple sample ATA low-level drivers.  </para>  </chapter>   <chapter id="libataDriverApi">     <title>libata Driver API</title>     <para>     struct ata_port_operations is defined for every low-level libata     hardware driver, and it controls how the low-level driver     interfaces with the ATA and SCSI layers.     </para>     <para>     FIS-based drivers will hook into the system with ->qc_prep() and     ->qc_issue() high-level hooks.  Hardware which behaves in a manner     similar to PCI IDE hardware may utilize several generic helpers,     defining at a bare minimum the bus I/O addresses of the ATA shadow     register blocks.     </para>     <sect1>        <title>struct ata_port_operations</title> 	<sect2><title>Disable ATA port</title>	<programlisting>void (*port_disable) (struct ata_port *);	</programlisting> 	<para>	Called from ata_bus_probe() and ata_bus_reset() error paths,	as well as when unregistering from the SCSI module (rmmod, hot	unplug).	This function should do whatever needs to be done to take the	port out of use.  In most cases, ata_port_disable() can be used	as this hook.	</para>	<para>	Called from ata_bus_probe() on a failed probe.	Called from ata_bus_reset() on a failed bus reset.	Called from ata_scsi_release().	</para> 	</sect2> 	<sect2><title>Post-IDENTIFY device configuration</title>	<programlisting>void (*dev_config) (struct ata_port *, struct ata_device *);	</programlisting> 	<para>	Called after IDENTIFY [PACKET] DEVICE is issued to each device	found.  Typically used to apply device-specific fixups prior to	issue of SET FEATURES - XFER MODE, and prior to operation.	</para>	<para>	Called by ata_device_add() after ata_dev_identify() determines	a device is present.	</para>	<para>	This entry may be specified as NULL in ata_port_operations.	</para> 	</sect2> 	<sect2><title>Set PIO/DMA mode</title>	<programlisting>void (*set_piomode) (struct ata_port *, struct ata_device *);void (*set_dmamode) (struct ata_port *, struct ata_device *);void (*post_set_mode) (struct ata_port *);unsigned int (*mode_filter) (struct ata_port *, struct ata_device *, unsigned int);	</programlisting> 	<para>	Hooks called prior to the issue of SET FEATURES - XFER MODE	command.  The optional ->mode_filter() hook is called when libata	has built a mask of the possible modes. This is passed to the 	->mode_filter() function which should return a mask of valid modes	after filtering those unsuitable due to hardware limits. It is not	valid to use this interface to add modes.	</para>	<para>	dev->pio_mode and dev->dma_mode are guaranteed to be valid when	->set_piomode() and when ->set_dmamode() is called. The timings for	any other drive sharing the cable will also be valid at this point.	That is the library records the decisions for the modes of each	drive on a channel before it attempts to set any of them.	</para>	<para>	->post_set_mode() is	called unconditionally, after the SET FEATURES - XFER MODE	command completes successfully.	</para> 	<para>	->set_piomode() is always called (if present), but	->set_dma_mode() is only called if DMA is possible.	</para> 	</sect2> 	<sect2><title>Taskfile read/write</title>	<programlisting>void (*tf_load) (struct ata_port *ap, struct ata_taskfile *tf);void (*tf_read) (struct ata_port *ap, struct ata_taskfile *tf);	</programlisting> 	<para>	->tf_load() is called to load the given taskfile into hardware	registers / DMA buffers.  ->tf_read() is called to read the	hardware registers / DMA buffers, to obtain the current set of	taskfile register values.	Most drivers for taskfile-based hardware (PIO or MMIO) use	ata_tf_load() and ata_tf_read() for these hooks.	</para> 	</sect2> 	<sect2><title>ATA command execute</title>	<programlisting>void (*exec_command)(struct ata_port *ap, struct ata_taskfile *tf);	</programlisting> 	<para>	causes an ATA command, previously loaded with	->tf_load(), to be initiated in hardware.	Most drivers for taskfile-based hardware use ata_exec_command()	for this hook.	</para> 	</sect2> 	<sect2><title>Per-cmd ATAPI DMA capabilities filter</title>	<programlisting>int (*check_atapi_dma) (struct ata_queued_cmd *qc);	</programlisting> 	<para>Allow low-level driver to filter ATA PACKET commands, returning a statusindicating whether or not it is OK to use DMA for the supplied PACKETcommand.	</para>	<para>	This hook may be specified as NULL, in which case libata will	assume that atapi dma can be supported.	</para> 	</sect2> 	<sect2><title>Read specific ATA shadow registers</title>	<programlisting>u8   (*check_status)(struct ata_port *ap);u8   (*check_altstatus)(struct ata_port *ap);u8   (*check_err)(struct ata_port *ap);	</programlisting> 	<para>	Reads the Status/AltStatus/Error ATA shadow register from	hardware.  On some hardware, reading the Status register has	the side effect of clearing the interrupt condition.	Most drivers for taskfile-based hardware use	ata_check_status() for this hook.	</para>	<para>	Note that because this is called from ata_device_add(), at	least a dummy function that clears device interrupts must be	provided for all drivers, even if the controller doesn't	actually have a taskfile status register.	</para> 	</sect2> 	<sect2><title>Select ATA device on bus</title>	<programlisting>void (*dev_select)(struct ata_port *ap, unsigned int device);	</programlisting> 	<para>	Issues the low-level hardware command(s) that causes one of N	hardware devices to be considered 'selected' (active and	available for use) on the ATA bus.  This generally has no	meaning on FIS-based devices.	</para>	<para>	Most drivers for taskfile-based hardware use	ata_std_dev_select() for this hook.  Controllers which do not	support second drives on a port (such as SATA contollers) will	use ata_noop_dev_select().	</para> 	</sect2> 	<sect2><title>Private tuning method</title>	<programlisting>void (*set_mode) (struct ata_port *ap);	</programlisting> 	<para>	By default libata performs drive and controller tuning in	accordance with the ATA timing rules and also applies blacklists	and cable limits. Some controllers need special handling and have	custom tuning rules, typically raid controllers that use ATA	commands but do not actually do drive timing.	</para> 	<warning>	<para>	This hook should not be used to replace the standard controller	tuning logic when a controller has quirks. Replacing the default	tuning logic in that case would bypass handling for drive and	bridge quirks that may be important to data reliability. If a	controller needs to filter the mode selection it should use the	mode_filter hook instead.	</para>	</warning> 	</sect2> 	<sect2><title>Reset ATA bus</title>	<programlisting>void (*phy_reset) (struct ata_port *ap);	</programlisting> 	<para>	The very first step in the probe phase.  Actions vary depending	on the bus type, typically.  After waking up the device and probing	for device presence (PATA and SATA), typically a soft reset	(SRST) will be performed.  Drivers typically use the helper	functions ata_bus_reset() or sata_phy_reset() for this hook.	Many SATA drivers use sata_phy_reset() or call it from within	their own phy_reset() functions.	</para> 	</sect2> 	<sect2><title>Control PCI IDE BMDMA engine</title>	<programlisting>void (*bmdma_setup) (struct ata_queued_cmd *qc);void (*bmdma_start) (struct ata_queued_cmd *qc);void (*bmdma_stop) (struct ata_port *ap);u8   (*bmdma_status) (struct ata_port *ap);	</programlisting> 	<para>When setting up an IDE BMDMA transaction, these hooks arm(->bmdma_setup), fire (->bmdma_start), and halt (->bmdma_stop)the hardware's DMA engine.  ->bmdma_status is used to read the standardPCI IDE DMA Status register.	</para> 	<para>These hooks are typically either no-ops, or simply not implemented, inFIS-based drivers.	</para>	<para>Most legacy IDE drivers use ata_bmdma_setup() for the bmdma_setup()hook.  ata_bmdma_setup() will write the pointer to the PRD table tothe IDE PRD Table Address register, enable DMA in the DMA Commandregister, and call exec_command() to begin the transfer.	</para>	<para>Most legacy IDE drivers use ata_bmdma_start() for the bmdma_start()hook.  ata_bmdma_start() will write the ATA_DMA_START flag to the DMACommand register.	</para>	<para>Many legacy IDE drivers use ata_bmdma_stop() for the bmdma_stop()hook.  ata_bmdma_stop() clears the ATA_DMA_START flag in the DMAcommand register.	</para>	<para>Many legacy IDE drivers use ata_bmdma_status() as the bmdma_status() hook.	</para> 	</sect2> 	<sect2><title>High-level taskfile hooks</title>	<programlisting>void (*qc_prep) (struct ata_queued_cmd *qc);int (*qc_issue) (struct ata_queued_cmd *qc);	</programlisting> 	<para>	Higher-level hooks, these two hooks can potentially supercede	several of the above taskfile/DMA engine hooks.  ->qc_prep is	called after the buffers have been DMA-mapped, and is typically	used to populate the hardware's DMA scatter-gather table.	Most drivers use the standard ata_qc_prep() helper function, but	more advanced drivers roll their own.	</para>	<para>	->qc_issue is used to make a command active, once the hardware	and S/G tables have been prepared.  IDE BMDMA drivers use the	helper function ata_qc_issue_prot() for taskfile protocol-based	dispatch.  More advanced drivers implement their own ->qc_issue.	</para>	<para>	ata_qc_issue_prot() calls ->tf_load(), ->bmdma_setup(), and	->bmdma_start() as necessary to initiate a transfer.	</para> 	</sect2> 	<sect2><title>Timeout (error) handling</title>	<programlisting>void (*eng_timeout) (struct ata_port *ap);	</programlisting> 	<para>This is a high level error handling function, called from theerror handling thread, when a command times out.  Most newerhardware will implement its own error handling code here.  IDE BMDMAdrivers may use the helper function ata_eng_timeout().	</para> 	</sect2> 	<sect2><title>Hardware interrupt handling</title>	<programlisting>irqreturn_t (*irq_handler)(int, void *, struct pt_regs *);void (*irq_clear) (struct ata_port *);	</programlisting> 	<para>	->irq_handler is the interrupt handling routine registered with	the system, by libata.  ->irq_clear is called during probe just	before the interrupt handler is registered, to be sure hardware	is quiet.	</para>	<para>	The second argument, dev_instance, should be cast to a pointer	to struct ata_host_set.	</para>	<para>	Most legacy IDE drivers use ata_interrupt() for the	irq_handler hook, which scans all ports in the host_set,	determines which queued command was active (if any), and calls	ata_host_intr(ap,qc).	</para>	<para>	Most legacy IDE drivers use ata_bmdma_irq_clear() for the	irq_clear() hook, which simply clears the interrupt and error	flags in the DMA status register.	</para> 	</sect2> 	<sect2><title>SATA phy read/write</title>	<programlisting>u32 (*scr_read) (struct ata_port *ap, unsigned int sc_reg);void (*scr_write) (struct ata_port *ap, unsigned int sc_reg,                   u32 val);	</programlisting> 	<para>	Read and write standard SATA phy registers.  Currently only used	if ->phy_reset hook called the sata_phy_reset() helper function.	sc_reg is one of SCR_STATUS, SCR_CONTROL, SCR_ERROR, or SCR_ACTIVE.	</para> 	</sect2> 	<sect2><title>Init and shutdown</title>	<programlisting>int (*port_start) (struct ata_port *ap);void (*port_stop) (struct ata_port *ap);void (*host_stop) (struct ata_host_set *host_set);	</programlisting> 	<para>	->port_start() is called just after the data structures for each	port are initialized.  Typically this is used to alloc per-port	DMA buffers / tables / rings, enable DMA engines, and similar	tasks.  Some drivers also use this entry point as a chance to	allocate driver-private memory for ap->private_data.	</para>	<para>	Many drivers use ata_port_start() as this hook or call	it from their own port_start() hooks.  ata_port_start()	allocates space for a legacy IDE PRD table and returns.	</para>	<para>	->port_stop() is called after ->host_stop().  It's sole function	is to release DMA/memory resources, now that they are no longer	actively being used.  Many drivers also free driver-private	data from port at this time.	</para>	<para>	Many drivers use ata_port_stop() as this hook, which frees the	PRD table.	</para>	<para>	->host_stop() is called after all ->port_stop() callshave completed.  The hook must finalize hardware shutdown, release DMAand other resources, etc.	This hook may be specified as NULL, in which case it is not called.	</para> 	</sect2>      </sect1>  </chapter>   <chapter id="libataEH">        <title>Error handling</title> 	<para>	This chapter describes how errors are handled under libata.	Readers are advised to read SCSI EH	(Documentation/scsi/scsi_eh.txt) and ATA exceptions doc first.	</para> 	<sect1><title>Origins of commands</title>	<para>	In libata, a command is represented with struct ata_queued_cmd	or qc.  qc's are preallocated during port initialization and	repetitively used for command executions.  Currently only one	qc is allocated per port but yet-to-be-merged NCQ branch	allocates one for each tag and maps each qc to NCQ tag 1-to-1.	</para>	<para>	libata commands can originate from two sources - libata itself	and SCSI midlayer.  libata internal commands are used for	initialization and error handling.  All normal blk requests	and commands for SCSI emulation are passed as SCSI commands	through queuecommand callback of SCSI host template.	</para>	</sect1> 	<sect1><title>How commands are issued</title> 	<variablelist> 	<varlistentry><term>Internal commands</term>	<listitem>	<para>	First, qc is allocated and initialized using	ata_qc_new_init().  Although ata_qc_new_init() doesn't	implement any wait or retry mechanism when qc is not	available, internal commands are currently issued only during	initialization and error recovery, so no other command is	active and allocation is guaranteed to succeed.	</para>	<para>	Once allocated qc's taskfile is initialized for the command to	be executed.  qc currently has two mechanisms to notify	completion.  One is via qc->complete_fn() callback and the

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