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

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Message-ID: <87efkta5yl.fsf@linux.intel.com>
Date:   Fri, 09 Mar 2018 12:39:14 +0200
From:   Felipe Balbi <balbi@...nel.org>
To:     Roger Quadros <rogerq@...com>, 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


Hi,

Roger Quadros <rogerq@...com> writes:
>>>>>> 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.

We can do that. And I think some 5ms is more than enough :-) I'd be
surprised if it takes anything over some 200us for the EndTransfer
command to complete.

-- 
balbi

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