linux-kernel - Re: [v4.2-rc1 Regression] usb: Enable LPM for USB 2.01+ full-speed devices

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Message-ID: <577D69BD.3070809@canonical.com>
Date:	Wed, 6 Jul 2016 16:27:41 -0400
From:	Joseph Salisbury <joseph.salisbury@...onical.com>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Greg KH <gregkh@...uxfoundation.org>, rtatiya@...eaurora.org,
	Robert Ancell <robert.ancell@...onical.com>,
	"mathias.nyman@...ux.intel.com" <mathias.nyman@...ux.intel.com>,
	chasemetzger15@...il.com, baolu.lu@...ux.intel.com,
	oneukum@...e.com, kborer@...il.com, jun.li@...escale.com,
	USB list <linux-usb@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [v4.2-rc1 Regression] usb: Enable LPM for USB 2.01+ full-speed
 devices

On 06/28/2016 11:40 AM, Alan Stern wrote:
> On Tue, 28 Jun 2016, Joseph Salisbury wrote:
>
>> On 06/24/2016 08:06 AM, Joseph Salisbury wrote:
>>> On 06/22/2016 12:14 PM, Greg KH wrote:
>>>> On Wed, Jun 22, 2016 at 11:38:43AM -0400, Joseph Salisbury wrote:
>>>>> Hi Rupesh,
>>>>>
>>>>> A kernel bug report was opened against Ubuntu [0].  After a kernel
>>>>> bisect, it was found that reverting the following commit resolved this bug:
>>>>>
>>>>> commit a8425292816ceaa8c49e29d2114e85d85a73e080
>>>>> Author: Rupesh Tatiya <rtatiya@...eaurora.org>
>>>>> Date:   Tue Apr 14 16:36:55 2015 +0530
>>>>>
>>>>>     usb: Enable LPM for USB 2.01+ full-speed devices
>>>>>
>>>>>
>>>>> The regression was introduced as of v4.2-rc1.
>>>>>
>>>>> I was hoping to get your feedback, since you are the patch author.  Do
>>>>> you think gathering any additional data will help diagnose this issue,
>>>>> or would it be best to submit a revert request?
>>>> Does the problem still happen with 4.7-rc4 or even 4.6?
>>>>
>>>> 4.2 is pretty old and obsolete you know :)
>>>>
>>>> thanks,
>>>>
>>>> greg k-h
>>> The regression does exist in 4.6-rc2.  I'll have the latest mainline
>>> 4.7-rc4 kernel tested.
>> The 4.7-rc4 kernel still exhibits the bug.
> Have you tried adding a NO_LPM quirk entry for this device, as I 
> suggested in an earlier email?  I can write a patch for this, if you 
> want.
>
> Alan Stern
>
Yes, adding a NO_LPM quirk entry resolves the bug.  I'll submit a patch
shortly, it is basically these lines added to usb_quirk_list[]:

+       /* ELAN Microelectronics Touchscreen */
+       { USB_DEVICE(0x04f3, 0x0381), .driver_info = USB_QUIRK_NO_LPM },

Thanks for the suggestion, Alan!