USB: Add a sysfs file to show LTM capabilities.

USB 3.0 devices can optionally support Latency Tolerance Messaging
(LTM).  Add a new sysfs file in the device directory to show whether a
device is LTM capable.  This file will be present for both USB 2.0 and
USB 3.0 devices.

Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>

1 files changed, 12 insertions, 0 deletions

diff --git a/Documentation/ABI/testing/sysfs-bus-usb b/Documentation/ABI/testing/sysfs-bus-usb
index 6df4e6f57560..5f75f8f7df34 100644
--- a/Documentation/ABI/testing/sysfs-bus-usb
+++ b/Documentation/ABI/testing/sysfs-bus-usb
@@ -208,3 +208,15 @@ Description:
                 such as ACPI. This file will read either "removable" or
                 "fixed" if the information is available, and "unknown"
                 otherwise.
+
+What:           /sys/bus/usb/devices/.../ltm_capable
+Date:           July 2012
+Contact:        Sarah Sharp <sarah.a.sharp@linux.intel.com>
+Description:
+                USB 3.0 devices may optionally support Latency Tolerance
+                Messaging (LTM).  They indicate their support by setting a bit
+                in the bmAttributes field of their SuperSpeed BOS descriptors.
+                If that bit is set for the device, ltm_capable will read "yes".
+                If the device doesn't support LTM, the file will read "no".
+                The file will be present for all speeds of USB devices, and will
+                always read "no" for USB 1.1 and USB 2.0 devices.