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

["Lu, Baolu" <baolu.lu@linux.intel.com>]

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@vger.kernel.org
>> Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
> ...
>
>> --- 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,
>>   		return;
>>   	}
>>   
>> -	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.

Thanks,
-Baolu

>
>> @@ -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",
>>   				usb3_lpm_names[state]);
>> +
>> +	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
>
>