[RFC v2] USB: Add a sysfs file to show LTM capabilities.

[Sarah Sharp <sarah.a.sharp@xxxxxxxxxxxxxxx>]

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@xxxxxxxxxxxxxxx>
---


v2: Add ABI documentation.

I think this is only change needed for the LPM bug fixes and LTM
patchset.  I did want to change the "xhci" prefix on the first two
patches to "USB", since they touch the USB core and not the xHCI driver.
However, I don't think that warrants a second revision to the mailing
list.

Greg, let me know if the ABI documentation seems ok, and I'll send you a
pull request.

Sarah


 Documentation/ABI/testing/sysfs-bus-usb |   12 ++++++++++++
 drivers/usb/core/hub.c                  |    7 -------
 drivers/usb/core/sysfs.c                |   10 ++++++++++
 include/linux/usb.h                     |    8 ++++++++
 4 files changed, 30 insertions(+), 7 deletions(-)

diff --git a/Documentation/ABI/testing/sysfs-bus-usb b/Documentation/ABI/testing/sysfs-bus-usb
index 6df4e6f..5f75f8f 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@xxxxxxxxxxxxxxx>
+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.
diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
index 7ca94d7..1f09018 100644
--- a/drivers/usb/core/hub.c
+++ b/drivers/usb/core/hub.c
@@ -2607,13 +2607,6 @@ static int check_port_resume_type(struct usb_device *udev,
 	return status;
 }
 
-static bool usb_device_supports_ltm(struct usb_device *udev)
-{
-	if (udev->speed != USB_SPEED_SUPER || !udev->bos || !udev->bos->ss_cap)
-		return false;
-	return udev->bos->ss_cap->bmAttributes & USB_LTM_SUPPORT;
-}
-
 int usb_disable_ltm(struct usb_device *udev)
 {
 	struct usb_hcd *hcd = bus_to_hcd(udev->bus);
diff --git a/drivers/usb/core/sysfs.c b/drivers/usb/core/sysfs.c
index 777f03c..682e825 100644
--- a/drivers/usb/core/sysfs.c
+++ b/drivers/usb/core/sysfs.c
@@ -253,6 +253,15 @@ show_removable(struct device *dev, struct device_attribute *attr, char *buf)
 }
 static DEVICE_ATTR(removable, S_IRUGO, show_removable, NULL);
 
+static ssize_t
+show_ltm_capable(struct device *dev, struct device_attribute *attr, char *buf)
+{
+	if (usb_device_supports_ltm(to_usb_device(dev)))
+		return sprintf(buf, "%s\n", "yes");
+	return sprintf(buf, "%s\n", "no");
+}
+static DEVICE_ATTR(ltm_capable, S_IRUGO, show_ltm_capable, NULL);
+
 #ifdef	CONFIG_PM
 
 static ssize_t
@@ -649,6 +658,7 @@ static struct attribute *dev_attrs[] = {
 	&dev_attr_authorized.attr,
 	&dev_attr_remove.attr,
 	&dev_attr_removable.attr,
+	&dev_attr_ltm_capable.attr,
 	NULL,
 };
 static struct attribute_group dev_attr_grp = {
diff --git a/include/linux/usb.h b/include/linux/usb.h
index aaac9e4..29147ca 100644
--- a/include/linux/usb.h
+++ b/include/linux/usb.h
@@ -631,6 +631,14 @@ extern void usb_unlocked_enable_lpm(struct usb_device *udev);
 extern int usb_disable_ltm(struct usb_device *udev);
 extern void usb_enable_ltm(struct usb_device *udev);
 
+static inline bool usb_device_supports_ltm(struct usb_device *udev)
+{
+	if (udev->speed != USB_SPEED_SUPER || !udev->bos || !udev->bos->ss_cap)
+		return false;
+	return udev->bos->ss_cap->bmAttributes & USB_LTM_SUPPORT;
+}
+
+
 /*-------------------------------------------------------------------------*/
 
 /* for drivers using iso endpoints */
-- 
1.7.9

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