linux-kernel - Re: [RFC] usb: host: xhci: Remove the watchdog timer and use command timer to watch stop endpoint command

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Message-ID: <CAMz4kuL=e3u-xwJxKMyqb3Y2Tu6+0nmxN4SQiosCv3GE0QdkxA@mail.gmail.com>
Date:   Thu, 1 Dec 2016 14:09:16 +0800
From:   Baolin Wang <baolin.wang@...aro.org>
To:     Lu Baolu <baolu.lu@...ux.intel.com>
Cc:     mathias.nyman@...el.com, Greg KH <gregkh@...uxfoundation.org>,
        USB <linux-usb@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Mark Brown <broonie@...nel.org>
Subject: Re: [RFC] usb: host: xhci: Remove the watchdog timer and use command
 timer to watch stop endpoint command

On 1 December 2016 at 14:04, Baolin Wang <baolin.wang@...aro.org> wrote:
> Hi Baolu,
>
> On 1 December 2016 at 13:45, Lu Baolu <baolu.lu@...ux.intel.com> wrote:
>> Hi,
>>
>> On 11/30/2016 05:02 PM, Baolin Wang wrote:
>>> If the hardware never responds to the stop endpoint command, the
>>> URBs will never be completed, and we might hang the USB subsystem.
>>> The original watchdog timer is used to watch if one stop endpoint
>>> command is timeout, if timeout, then the watchdog timer will set
>>> XHCI_STATE_DYING, try to halt the xHCI host, and give back all
>>> pending URBs.
>>>
>>> But now we already have one command timer to control command timeout,
>>> thus we can also use the command timer to watch the stop endpoint
>>> command, instead of one duplicate watchdog timer which need to be
>>> removed.
>>>
>>> Meanwhile we don't need the 'stop_cmds_pending' flag to identy if
>>> this is the last stop endpoint command of one endpoint. Since we
>>> can make sure we only set one stop endpoint command for one endpoint
>>> by 'EP_HALT_PENDING' flag in xhci_urb_dequeue() function. Thus remove
>>> this flag.
>>
>> I am afraid you can't do this. "stop_cmds_pending" was added
>> to fix the problem described in the comments that you want to
>> remove. But I didn't find any fix of this problem in your patch.
>
> Now we can not pending another stop endpoint command for the same one
> endpoint, since will check 'EP_HALT_PENDING' flag in
> xhci_urb_dequeue() function to avoid this. But after some
> investigation, I think I missed the stop endpoint command in
> xhci_stop_device() which did not check the 'EP_HALT_PENDING' flag,
> maybe need to add 'EP_HALT_PENDING' flag checking in
> xhci_stop_device() function. DId I miss something else? Thanks.

Sorry, wait, we will wait for the stop endpoint command finished in
xhci_stop_device() function. So we don't need check 'EP_HALT_PENDING'
flag as the orignal code did.

-- 
Baolin.wang
Best Regards