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 11:28 PM, Alan Stern wrote:
> On Fri, 13 Nov 2015, Lu, Baolu wrote:
>
>> 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.
> Then maybe you can add a comment explaining this.

Yes, I will add comments for this.

>
> The patch still looks strange, though.  Your new code does this:
>
> 	ret = usb_set_lpm_timeout(...);
> 	if (ret)
> 		...
> 	else if (udev->actconfig)
> 		...
> 	if (!ret) {
> 		if (state == USB3_LPM_U1)
> 		...
> 	}
>
> It would be better to do this:
>
> 	if (usb_set_lpm_timeout(...)) {
> 		...
> 	} else {
> 		if (udev->actconfig)
> 			...
> 		if (state == USB3_LPM_U1)
> 		...
> 	}

Yes, this looks better. I will refactor this part of code.

>
> Alan Stern
>

Thank you.
-Baolu