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

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Date:   Fri, 09 Mar 2018 11:23:19 +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:

<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?

-- 
balbi

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