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>

4 files changed, 30 insertions, 7 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.
diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
index b5bd6bd8fd12..d739f966b5a8 100644
--- a/drivers/usb/core/hub.c
+++ b/drivers/usb/core/hub.c
@@ -2610,13 +2610,6 @@ 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 777f03c37725..682e8256b95d 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 f29831bad235..f8506ed0f97b 100644
--- a/include/linux/usb.h
+++ b/include/linux/usb.h
@@ -636,6 +636,14 @@ 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 */