linux-kernel - Re: [PATCH] usb: dwc3: Prevent indefinite sleep in _dwc3_set

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Date:   Fri, 9 Mar 2018 11:49:56 +0200
From:   Roger Quadros <rogerq@...com>
To:     Felipe Balbi <balbi@...nel.org>,
        Baolin Wang <baolin.wang@...aro.org>
CC:     USB <linux-usb@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] usb: dwc3: Prevent indefinite sleep in _dwc3_set_mode
 during suspend/resume

On 09/03/18 11:26, Roger Quadros wrote:
> On 09/03/18 11:23, Felipe Balbi wrote:
>>
>> Hi,
>>
>> Roger Quadros <rogerq@...com> writes:
>>
>> <snip>
>>
>>>>> When we set up the DWC3_DEPCMD_ENDTRANSFER command in
>>>>> dwc3_stop_active_transfer(), we can do not set DWC3_DEPCMD_CMDIOC,
>>>>> then there will no endpoint command complete interrupts I think.
>>>>>
>>>>> cmd |= DWC3_DEPCMD_CMDIOC;
>>>>
>>>> I remember some part of the databook mandating CMDIOC to be set. We
>>>> could test it out without and see if anything blows up. I would,
>>>> however, require a lengthy comment explaining that we're deviating from
>>>> databook revision x.yya, section foobar because $reasons. :-)
>>>>
>>>
>>> This is what the v3.10 databook says
>>>
>>> "When issuing an End Transfer command, software must set the CmdIOC
>>> bit (field 8) so that an Endpoint Command Complete event is generated
>>> after the transfer ends. This is necessary to synchronize the
>>> conclusion of system bus traffic before the End Transfer command is
>>> completed."
>>>
>>> with a note
>>>
>>> "If GUCTL2[Rst_actbitlater] is set, Software can poll the completion
>>> of the End Transfer command by polling the command active bit to be
>>> cleared to 0."
>>>
>>> fyi.
>>>
>>> Rst_actbitlater - "Enable clearing of the command active bit for the
>>> ENDXFER command after the command execution is completed.  This bit is
>>> valid in device mode only."
>>>
>>> So I'd prefer not to clear CMDIOC for all cases.
>>>
>>> Could we some how just tackle the dwc3_gadget_exit case like I did in
>>> this patch?
>>
>> if you can send a version that doesn't iterate over all endpoints twice,
>> sure. We still need a comment somewhere, and I fear we may get
>> interrupts later in some cases. How would we deal with that?
>>
> 
> how about explicitly masking that interrupt? Is it possible?
> 

Other easy option is to use wait_event_interruptible_lock_irq_timeout()
instead of wait_event_lock_irq() in dwc3_gadget_stop().

Is a 200ms timeout sufficient? And after the first timeout we assume all
will timeout so no point in waiting 200ms for each endpoint.

-- 
cheers,
-roger

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