465 lines
14 KiB
XML
465 lines
14 KiB
XML
<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN"
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"http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" []>
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<book id="libataDevGuide">
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<bookinfo>
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<title>libATA Developer's Guide</title>
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<authorgroup>
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<author>
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<firstname>Jeff</firstname>
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<surname>Garzik</surname>
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</author>
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</authorgroup>
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<copyright>
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<year>2003-2005</year>
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<holder>Jeff Garzik</holder>
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</copyright>
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<legalnotice>
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<para>
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The contents of this file are subject to the Open
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Software License version 1.1 that can be found at
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<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
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by reference.
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</para>
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<para>
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Alternatively, the contents of this file may be used under the terms
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of the GNU General Public License version 2 (the "GPL") as distributed
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in the kernel source COPYING file, in which case the provisions of
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the GPL are applicable instead of the above. If you wish to allow
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the use of your version of this file only under the terms of the
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GPL and not to allow others to use your version of this file under
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the OSL, indicate your decision by deleting the provisions above and
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replace them with the notice and other provisions required by the GPL.
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If you do not delete the provisions above, a recipient may use your
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version of this file under either the OSL or the GPL.
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</para>
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</legalnotice>
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</bookinfo>
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<toc></toc>
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<chapter id="libataIntroduction">
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<title>Introduction</title>
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<para>
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libATA is a library used inside the Linux kernel to support ATA host
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controllers and devices. libATA provides an ATA driver API, class
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transports for ATA and ATAPI devices, and SCSI<->ATA translation
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for ATA devices according to the T10 SAT specification.
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</para>
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<para>
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This Guide documents the libATA driver API, library functions, library
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internals, and a couple sample ATA low-level drivers.
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</para>
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</chapter>
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<chapter id="libataDriverApi">
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<title>libata Driver API</title>
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<para>
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struct ata_port_operations is defined for every low-level libata
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hardware driver, and it controls how the low-level driver
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interfaces with the ATA and SCSI layers.
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</para>
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<para>
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FIS-based drivers will hook into the system with ->qc_prep() and
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->qc_issue() high-level hooks. Hardware which behaves in a manner
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similar to PCI IDE hardware may utilize several generic helpers,
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defining at a bare minimum the bus I/O addresses of the ATA shadow
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register blocks.
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</para>
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<sect1>
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<title>struct ata_port_operations</title>
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<sect2><title>Disable ATA port</title>
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<programlisting>
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void (*port_disable) (struct ata_port *);
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</programlisting>
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<para>
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Called from ata_bus_probe() and ata_bus_reset() error paths,
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as well as when unregistering from the SCSI module (rmmod, hot
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unplug).
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This function should do whatever needs to be done to take the
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port out of use. In most cases, ata_port_disable() can be used
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as this hook.
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</para>
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<para>
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Called from ata_bus_probe() on a failed probe.
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Called from ata_bus_reset() on a failed bus reset.
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Called from ata_scsi_release().
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</para>
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</sect2>
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<sect2><title>Post-IDENTIFY device configuration</title>
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<programlisting>
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void (*dev_config) (struct ata_port *, struct ata_device *);
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</programlisting>
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<para>
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Called after IDENTIFY [PACKET] DEVICE is issued to each device
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found. Typically used to apply device-specific fixups prior to
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issue of SET FEATURES - XFER MODE, and prior to operation.
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</para>
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<para>
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Called by ata_device_add() after ata_dev_identify() determines
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a device is present.
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</para>
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<para>
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This entry may be specified as NULL in ata_port_operations.
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</para>
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</sect2>
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<sect2><title>Set PIO/DMA mode</title>
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<programlisting>
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void (*set_piomode) (struct ata_port *, struct ata_device *);
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void (*set_dmamode) (struct ata_port *, struct ata_device *);
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void (*post_set_mode) (struct ata_port *ap);
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</programlisting>
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<para>
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Hooks called prior to the issue of SET FEATURES - XFER MODE
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command. dev->pio_mode is guaranteed to be valid when
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->set_piomode() is called, and dev->dma_mode is guaranteed to be
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valid when ->set_dmamode() is called. ->post_set_mode() is
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called unconditionally, after the SET FEATURES - XFER MODE
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command completes successfully.
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</para>
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<para>
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->set_piomode() is always called (if present), but
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->set_dma_mode() is only called if DMA is possible.
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</para>
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</sect2>
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<sect2><title>Taskfile read/write</title>
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<programlisting>
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void (*tf_load) (struct ata_port *ap, struct ata_taskfile *tf);
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void (*tf_read) (struct ata_port *ap, struct ata_taskfile *tf);
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</programlisting>
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<para>
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->tf_load() is called to load the given taskfile into hardware
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registers / DMA buffers. ->tf_read() is called to read the
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hardware registers / DMA buffers, to obtain the current set of
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taskfile register values.
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Most drivers for taskfile-based hardware (PIO or MMIO) use
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ata_tf_load() and ata_tf_read() for these hooks.
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</para>
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</sect2>
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<sect2><title>ATA command execute</title>
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<programlisting>
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void (*exec_command)(struct ata_port *ap, struct ata_taskfile *tf);
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</programlisting>
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<para>
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causes an ATA command, previously loaded with
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->tf_load(), to be initiated in hardware.
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Most drivers for taskfile-based hardware use ata_exec_command()
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for this hook.
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</para>
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</sect2>
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<sect2><title>Per-cmd ATAPI DMA capabilities filter</title>
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<programlisting>
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int (*check_atapi_dma) (struct ata_queued_cmd *qc);
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</programlisting>
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<para>
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Allow low-level driver to filter ATA PACKET commands, returning a status
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indicating whether or not it is OK to use DMA for the supplied PACKET
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command.
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</para>
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<para>
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This hook may be specified as NULL, in which case libata will
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assume that atapi dma can be supported.
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</para>
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</sect2>
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<sect2><title>Read specific ATA shadow registers</title>
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<programlisting>
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u8 (*check_status)(struct ata_port *ap);
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u8 (*check_altstatus)(struct ata_port *ap);
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u8 (*check_err)(struct ata_port *ap);
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</programlisting>
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<para>
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Reads the Status/AltStatus/Error ATA shadow register from
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hardware. On some hardware, reading the Status register has
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the side effect of clearing the interrupt condition.
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Most drivers for taskfile-based hardware use
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ata_check_status() for this hook.
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</para>
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<para>
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Note that because this is called from ata_device_add(), at
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least a dummy function that clears device interrupts must be
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provided for all drivers, even if the controller doesn't
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actually have a taskfile status register.
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</para>
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</sect2>
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<sect2><title>Select ATA device on bus</title>
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<programlisting>
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void (*dev_select)(struct ata_port *ap, unsigned int device);
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</programlisting>
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<para>
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Issues the low-level hardware command(s) that causes one of N
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hardware devices to be considered 'selected' (active and
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available for use) on the ATA bus. This generally has no
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meaning on FIS-based devices.
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</para>
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<para>
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Most drivers for taskfile-based hardware use
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ata_std_dev_select() for this hook. Controllers which do not
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support second drives on a port (such as SATA contollers) will
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use ata_noop_dev_select().
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</para>
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</sect2>
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<sect2><title>Reset ATA bus</title>
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<programlisting>
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void (*phy_reset) (struct ata_port *ap);
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</programlisting>
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<para>
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The very first step in the probe phase. Actions vary depending
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on the bus type, typically. After waking up the device and probing
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for device presence (PATA and SATA), typically a soft reset
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(SRST) will be performed. Drivers typically use the helper
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functions ata_bus_reset() or sata_phy_reset() for this hook.
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Many SATA drivers use sata_phy_reset() or call it from within
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their own phy_reset() functions.
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</para>
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</sect2>
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<sect2><title>Control PCI IDE BMDMA engine</title>
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<programlisting>
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void (*bmdma_setup) (struct ata_queued_cmd *qc);
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void (*bmdma_start) (struct ata_queued_cmd *qc);
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void (*bmdma_stop) (struct ata_port *ap);
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u8 (*bmdma_status) (struct ata_port *ap);
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</programlisting>
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<para>
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When setting up an IDE BMDMA transaction, these hooks arm
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(->bmdma_setup), fire (->bmdma_start), and halt (->bmdma_stop)
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the hardware's DMA engine. ->bmdma_status is used to read the standard
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PCI IDE DMA Status register.
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</para>
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<para>
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These hooks are typically either no-ops, or simply not implemented, in
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FIS-based drivers.
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</para>
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<para>
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Most legacy IDE drivers use ata_bmdma_setup() for the bmdma_setup()
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hook. ata_bmdma_setup() will write the pointer to the PRD table to
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the IDE PRD Table Address register, enable DMA in the DMA Command
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register, and call exec_command() to begin the transfer.
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</para>
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<para>
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Most legacy IDE drivers use ata_bmdma_start() for the bmdma_start()
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hook. ata_bmdma_start() will write the ATA_DMA_START flag to the DMA
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Command register.
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</para>
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<para>
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Many legacy IDE drivers use ata_bmdma_stop() for the bmdma_stop()
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hook. ata_bmdma_stop() clears the ATA_DMA_START flag in the DMA
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command register.
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</para>
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<para>
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Many legacy IDE drivers use ata_bmdma_status() as the bmdma_status() hook.
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</para>
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</sect2>
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<sect2><title>High-level taskfile hooks</title>
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<programlisting>
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void (*qc_prep) (struct ata_queued_cmd *qc);
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int (*qc_issue) (struct ata_queued_cmd *qc);
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</programlisting>
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<para>
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Higher-level hooks, these two hooks can potentially supercede
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several of the above taskfile/DMA engine hooks. ->qc_prep is
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called after the buffers have been DMA-mapped, and is typically
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used to populate the hardware's DMA scatter-gather table.
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Most drivers use the standard ata_qc_prep() helper function, but
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more advanced drivers roll their own.
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</para>
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<para>
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->qc_issue is used to make a command active, once the hardware
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and S/G tables have been prepared. IDE BMDMA drivers use the
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helper function ata_qc_issue_prot() for taskfile protocol-based
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dispatch. More advanced drivers implement their own ->qc_issue.
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</para>
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<para>
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ata_qc_issue_prot() calls ->tf_load(), ->bmdma_setup(), and
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->bmdma_start() as necessary to initiate a transfer.
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</para>
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</sect2>
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<sect2><title>Timeout (error) handling</title>
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<programlisting>
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void (*eng_timeout) (struct ata_port *ap);
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</programlisting>
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<para>
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This is a high level error handling function, called from the
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error handling thread, when a command times out. Most newer
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hardware will implement its own error handling code here. IDE BMDMA
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drivers may use the helper function ata_eng_timeout().
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</para>
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</sect2>
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<sect2><title>Hardware interrupt handling</title>
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<programlisting>
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irqreturn_t (*irq_handler)(int, void *, struct pt_regs *);
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void (*irq_clear) (struct ata_port *);
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</programlisting>
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<para>
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->irq_handler is the interrupt handling routine registered with
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the system, by libata. ->irq_clear is called during probe just
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before the interrupt handler is registered, to be sure hardware
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is quiet.
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</para>
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<para>
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The second argument, dev_instance, should be cast to a pointer
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to struct ata_host_set.
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</para>
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<para>
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Most legacy IDE drivers use ata_interrupt() for the
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irq_handler hook, which scans all ports in the host_set,
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determines which queued command was active (if any), and calls
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ata_host_intr(ap,qc).
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</para>
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<para>
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Most legacy IDE drivers use ata_bmdma_irq_clear() for the
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irq_clear() hook, which simply clears the interrupt and error
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flags in the DMA status register.
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</para>
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</sect2>
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<sect2><title>SATA phy read/write</title>
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<programlisting>
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u32 (*scr_read) (struct ata_port *ap, unsigned int sc_reg);
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void (*scr_write) (struct ata_port *ap, unsigned int sc_reg,
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u32 val);
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</programlisting>
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<para>
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Read and write standard SATA phy registers. Currently only used
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if ->phy_reset hook called the sata_phy_reset() helper function.
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sc_reg is one of SCR_STATUS, SCR_CONTROL, SCR_ERROR, or SCR_ACTIVE.
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</para>
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</sect2>
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<sect2><title>Init and shutdown</title>
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<programlisting>
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int (*port_start) (struct ata_port *ap);
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void (*port_stop) (struct ata_port *ap);
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void (*host_stop) (struct ata_host_set *host_set);
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</programlisting>
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<para>
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->port_start() is called just after the data structures for each
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port are initialized. Typically this is used to alloc per-port
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DMA buffers / tables / rings, enable DMA engines, and similar
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tasks. Some drivers also use this entry point as a chance to
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allocate driver-private memory for ap->private_data.
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</para>
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<para>
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Many drivers use ata_port_start() as this hook or call
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it from their own port_start() hooks. ata_port_start()
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allocates space for a legacy IDE PRD table and returns.
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</para>
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<para>
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->port_stop() is called after ->host_stop(). It's sole function
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is to release DMA/memory resources, now that they are no longer
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actively being used. Many drivers also free driver-private
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data from port at this time.
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</para>
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<para>
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Many drivers use ata_port_stop() as this hook, which frees the
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PRD table.
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</para>
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<para>
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->host_stop() is called after all ->port_stop() calls
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have completed. The hook must finalize hardware shutdown, release DMA
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and other resources, etc.
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This hook may be specified as NULL, in which case it is not called.
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</para>
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</sect2>
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</sect1>
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</chapter>
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<chapter id="libataExt">
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<title>libata Library</title>
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!Edrivers/scsi/libata-core.c
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</chapter>
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<chapter id="libataInt">
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<title>libata Core Internals</title>
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!Idrivers/scsi/libata-core.c
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</chapter>
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<chapter id="libataScsiInt">
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<title>libata SCSI translation/emulation</title>
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!Edrivers/scsi/libata-scsi.c
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!Idrivers/scsi/libata-scsi.c
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</chapter>
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<chapter id="PiixInt">
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<title>ata_piix Internals</title>
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!Idrivers/scsi/ata_piix.c
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</chapter>
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<chapter id="SILInt">
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<title>sata_sil Internals</title>
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!Idrivers/scsi/sata_sil.c
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</chapter>
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<chapter id="libataThanks">
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<title>Thanks</title>
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<para>
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The bulk of the ATA knowledge comes thanks to long conversations with
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Andre Hedrick (www.linux-ide.org), and long hours pondering the ATA
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and SCSI specifications.
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</para>
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<para>
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Thanks to Alan Cox for pointing out similarities
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between SATA and SCSI, and in general for motivation to hack on
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libata.
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</para>
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<para>
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libata's device detection
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method, ata_pio_devchk, and in general all the early probing was
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based on extensive study of Hale Landis's probe/reset code in his
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ATADRVR driver (www.ata-atapi.com).
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</para>
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</chapter>
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</book>
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