Re: [PATCH v2 1/3] usb: core: lpm: fix usb3_hardware_lpm sysfs node

From: Lu, Baolu
Date: Fri Nov 13 2015 - 00:55:24 EST

On 11/13/2015 12:20 AM, Alan Stern wrote:
On Thu, 12 Nov 2015, Lu Baolu wrote:

Commit 655fe4effe0f ("usbcore: add sysfs support to xHCI usb3
hardware LPM") introduced usb3_hardware_lpm sysfs node. This
doesn't show the correct status of USB3 U1 and U2 LPM status.

This patch fixes this by replacing usb3_hardware_lpm with two
nodes, usb3_hardware_lpm_u1 (for U1) and usb3_hardware_lpm_u2
(for U2), and recording the U1/U2 LPM status in right places.

This patch should be back-ported to kernels as old as 4.3,
that contains Commit 655fe4effe0f ("usbcore: add sysfs support
to xHCI usb3 hardware LPM").

Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Lu Baolu <>

--- a/drivers/usb/core/hub.c
+++ b/drivers/usb/core/hub.c
@@ -3875,17 +3875,23 @@ static void usb_enable_link_state(struct usb_hcd *hcd, struct usb_device *udev,
- if (usb_set_lpm_timeout(udev, state, timeout))
+ ret = usb_set_lpm_timeout(udev, state, timeout);
+ if (ret)
/* If we can't set the parent hub U1/U2 timeout,
* device-initiated LPM won't be allowed either, so let the xHCI
* host know that this link state won't be enabled.
hcd->driver->disable_usb3_lpm_timeout(hcd, udev, state);
/* Only a configured device will accept the Set Feature U1/U2_ENABLE */
else if (udev->actconfig)
usb_set_device_initiated_lpm(udev, state, true);
+ if (!ret) {
+ if (state == USB3_LPM_U1)
+ udev->usb3_lpm_u1_enabled = 1;
+ else if (state == USB3_LPM_U2)
+ udev->usb3_lpm_u2_enabled = 1;
+ }
This doesn't look right at all. What happens if ret is 0 but the
device isn't configured? You'll set the usb3_lpm_u*_enabled flag even
though LPM isn't really enabled.

Don't you want to set these flags inside the
usb_set_device_initiated_lpm() function, where you know whether the
action succeeded? And leave this routine unchanged?

My understand is that both hub and device can initiate LPM.
As soon as usb_set_lpm_timeout(valid_timeout_value)
returns 0, the hub-initiated LPM is enabled. Thus, LPM is
enabled no matter the result of usb_set_device_initiated_lpm().
The only difference is whether device is able to initiate LPM.

On disable side, as soon as usb_set_lpm_timeout(0) return 0,
hub initiated LPM is disabled. Hub will disallows link to enter
U1/U2 as well, even device is initiating LPM. Hence LPM
is disabled as soon as hub LPM timeout set to 0, no matter
device-initiated LPM is disabled or not.


@@ -3925,6 +3931,12 @@ static int usb_disable_link_state(struct usb_hcd *hcd, struct usb_device *udev,
dev_warn(&udev->dev, "Could not disable xHCI %s timeout, "
"bus schedule bandwidth may be impacted.\n",
+ if (state == USB3_LPM_U1)
+ udev->usb3_lpm_u1_enabled = 0;
+ else if (state == USB3_LPM_U2)
+ udev->usb3_lpm_u2_enabled = 0;
return 0;
And then this won't be necessary.

Alan Stern

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