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Commit 024f117c authored by Sarah Sharp's avatar Sarah Sharp
Browse files

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: default avatarSarah Sharp <sarah.a.sharp@linux.intel.com>
parent f74631e3

Documentation/ABI/testing/sysfs-bus-usb

+12 −0
Original line number Diff line number Diff line
@@ -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.

drivers/usb/core/hub.c

+0 −7
Original line number Diff line number Diff line
@@ -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);

drivers/usb/core/sysfs.c

+10 −0
Original line number Diff line number Diff line
@@ -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 = {

include/linux/usb.h

+8 −0
Original line number Diff line number Diff line
@@ -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 */