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+What: /sys/class/ata_...
+Date: August 2008
+Contact: Gwendal Grignou<gwendal@google.com>
+Description:
+
+Provide a place in sysfs for storing the ATA topology of the system. This allows
+retrieving various information about ATA objects.
+
+Files under /sys/class/ata_port
+-------------------------------
+
+ For each port, a directory ataX is created where X is the ata_port_id of
+ the port. The device parent is the ata host device.
+
+idle_irq (read)
+
+ Number of IRQ received by the port while idle [some ata HBA only].
+
+nr_pmp_links (read)
+
+ If a SATA Port Multiplier (PM) is connected, number of link behind it.
+
+Files under /sys/class/ata_link
+-------------------------------
+
+ Behind each port, there is a ata_link. If there is a SATA PM in the
+ topology, 15 ata_link objects are created.
+
+ If a link is behind a port, the directory name is linkX, where X is
+ ata_port_id of the port.
+ If a link is behind a PM, its name is linkX.Y where X is ata_port_id
+ of the parent port and Y the PM port.
+
+hw_sata_spd_limit
+
+ Maximum speed supported by the connected SATA device.
+
+sata_spd_limit
+
+ Maximum speed imposed by libata.
+
+sata_spd
+
+ Current speed of the link [1.5, 3Gps,...].
+
+Files under /sys/class/ata_device
+---------------------------------
+
+ Behind each link, up to two ata device are created.
+ The name of the directory is devX[.Y].Z where:
+ - X is ata_port_id of the port where the device is connected,
+ - Y the port of the PM if any, and
+ - Z the device id: for PATA, there is usually 2 devices [0,1],
+ only 1 for SATA.
+
+class
+ Device class. Can be "ata" for disk, "atapi" for packet device,
+ "pmp" for PM, or "none" if no device was found behind the link.
+
+dma_mode
+
+ Transfer modes supported by the device when in DMA mode.
+ Mostly used by PATA device.
+
+pio_mode
+
+ Transfer modes supported by the device when in PIO mode.
+ Mostly used by PATA device.
+
+xfer_mode
+
+ Current transfer mode.
+
+id
+
+ Cached result of IDENTIFY command, as described in ATA8 7.16 and 7.17.
+ Only valid if the device is not a PM.
+
+gscr
+
+ Cached result of the dump of PM GSCR register.
+ Valid registers are:
+ 0: SATA_PMP_GSCR_PROD_ID,
+ 1: SATA_PMP_GSCR_REV,
+ 2: SATA_PMP_GSCR_PORT_INFO,
+ 32: SATA_PMP_GSCR_ERROR,
+ 33: SATA_PMP_GSCR_ERROR_EN,
+ 64: SATA_PMP_GSCR_FEAT,
+ 96: SATA_PMP_GSCR_FEAT_EN,
+ 130: SATA_PMP_GSCR_SII_GPIO
+ Only valid if the device is a PM.
+
+spdn_cnt
+
+ Number of time libata decided to lower the speed of link due to errors.
+
+ering
+
+ Formatted output of the error ring of the device.