[PATCH 25/25] Documentation: sysfs-block-device: document command duration limits

[Niklas Cassel]

From: Damien Le Moal <damien.lemoal@xxxxxxxxxxxxxxxxxx>

Document ABI/testing/sysfs-block-device the sysfs attributes present
under /sys/block/*/device/duration_limits for ATA and SCSI devices
supporting the command duration limits feature.

Signed-off-by: Damien Le Moal <damien.lemoal@xxxxxxxxxxxxxxxxxx>
---
 Documentation/ABI/testing/sysfs-block-device | 143 +++++++++++++++++++
 1 file changed, 143 insertions(+)

diff --git a/Documentation/ABI/testing/sysfs-block-device b/Documentation/ABI/testing/sysfs-block-device
index 7ac7b19b2f72..44841f91c69b 100644
--- a/Documentation/ABI/testing/sysfs-block-device
+++ b/Documentation/ABI/testing/sysfs-block-device
@@ -95,3 +95,146 @@ Description:
 		This file does not exist if the HBA driver does not implement
 		support for the SATA NCQ priority feature, regardless of the
 		device support for this feature.
+
+
+What:		/sys/block/*/device/duration_limits/enable
+Date:		Dec, 2022
+KernelVersion:	v6.3
+Contact:	linux-scsi@xxxxxxxxxxxxxxx
+Description:
+		(RW) For ATA and SCSI devices supporting the command duration
+		limits feature, write to the file to turn on or off the
+		feature. By default this feature is turned off. If the device
+		does not support the command duration limits feature, this
+		attribute does not exist (the directory
+		"/sys/block/*/device/duration_limits" does not exist).
+		Writing "1" to this file enables the use of command duration
+		limits for read and write commands in the kernel and turns on
+		the feature on the device. Writing "0" disables the feature.
+
+
+What:		/sys/block/*/device/duration_limits/read/[1-7]/*
+Date:		Dec, 2022
+KernelVersion:	v6.3
+Contact:	linux-scsi@xxxxxxxxxxxxxxx
+Description:
+		(RO) For ATA and SCSI devices supporting the command duration
+		limits feature, this shows the set of 7 command duration limits
+		descriptors for read commands currently set on the device. For
+		each of the 7 descritors, the following read-only attributes
+		are present:
+
+		  - duration_guideline: specifies the preferred length of time
+		    in microseconds for the completion of a command.
+
+		  - duration_guideline_policy: specifies the policy action
+		    taken if the duration_guideline attribute specifies a
+		    non-zero command duration guideline that the device is
+		    unable to achieve for a command.
+
+		    Possible values are:
+
+		      - 0x0: The device will complete the command at the
+			     earliest possible time consistent with the
+			     specified command duration guideline.
+		      - 0x1: If the specified command duration guideline has
+			     not been achieved and the command duration
+			     guideline policy field is not the seventh command
+			     duration limits descriptor, then the device
+			     continues processing that command using the
+			     command duration limits descriptor that has
+			     the next higher number.
+		      - 0x2: The device will continue processing the command
+			     as with no command duration limits descriptor
+			     being used.
+		      - 0xD: The device will complete the command and an IO
+			     failure will be reported to the user with the ETIME
+			     error code.
+		      - 0xF: Same as 0xD.
+
+		  - max_active_time: specifies an upper limit in microseconds
+		    on the time that elapses from the time at which the device
+		    initiates actions to access, transfer, or act upon the
+		    specified data until the time the device returns status for
+		    the command.
+
+		  - max_active_time_policy: specifies the policy action taken
+		    if the time used to process a command exceeds a non-zero
+		    time specified by the max_active_time attribute.
+
+		    Possible values are:
+
+		      - 0x0: The device will complete the command at the
+			     earliest possible time (i.e, do nothing based on
+			     the max limit not being met).
+		      - 0xD: The device will complete the command and an IO
+			     failure will be reported to the user with the ETIME
+			     error code.
+		      - 0xE: Same as 0xD.
+		      - 0xF: Same as 0xD.
+
+		  - max_inactive_time: specifies an upper limit in microseconds
+		    on the time that elapses from the time at which the device
+		    receives the command until the time at which the device
+		    initiates actions to access, transfer, or act upon the
+		    specified data.
+
+		  - max_inactive_time_policy: specifies the policy action taken
+		    if a non-zero max_inactive_time limit is not met.
+
+		    Possible values are:
+
+		      - 0x0: The device will complete the command at the
+			     earliest possible time (i.e, do nothing based on
+			     the time limit not being met).
+		      - 0xD: The device will complete the command and an IO
+			     failure will be reported to the user with the ETIME
+			     error code.
+		      - 0xF: Same as 0xD.
+
+
+What:		/sys/block/*/device/duration_limits/read/page
+Date:		Dec, 2022
+KernelVersion:	v6.3
+Contact:	linux-scsi@xxxxxxxxxxxxxxx
+Description:
+		(RO) For ATA and SCSI devices supporting the command duration
+		limits feature, this shows the name of the device VPD page
+		specifying the set of 7 command duration limits descriptors for
+		read commands. Possible values are "T2A" and "T2B".
+
+
+What:		/sys/block/*/device/duration_limits/write/[1-7]/*
+Date:		Dec, 2022
+KernelVersion:	v6.3
+Contact:	linux-scsi@xxxxxxxxxxxxxxx
+Description:
+		(RO) For ATA and SCSI devices supporting the command duration
+		limits feature, this shows the set of 7 command duration limits
+		descriptors for write commands currently set on the device. For
+		each of the 7 descritors, the same set of read-only attributes
+		as for read commands is present.
+
+
+What:		/sys/block/*/device/duration_limits/write/page
+Date:		Dec, 2022
+KernelVersion:	v6.3
+Contact:	linux-scsi@xxxxxxxxxxxxxxx
+Description:
+		(RO) For ATA and SCSI devices supporting the command duration
+		limits feature, this shows the name of the device VPD page
+		specifying the set of 7 command duration limits descriptors for
+		write commands. Possible values are "T2A" and "T2B".
+
+
+What:		/sys/block/*/device/duration_limits/perf_vs_duration_guideline
+Date:		Dec, 2022
+KernelVersion:	v6.3
+Contact:	linux-scsi@xxxxxxxxxxxxxxx
+Description:
+		(RO) For ATA and SCSI devices supporting the command duration
+		limits feature, this specifies the maximum percentage increase
+		in average command completion times (reduction in IOPS) that
+		is allowed for the device to perform actions based on the
+		contents of the duration guideline field in every command
+		duration limit descriptor for both read and write commands.
-- 
2.38.1