linux-kernel - Re: [RFC PATCH v2 1/3] usb: dwc3: Flush pending SETUP data during stop active xfers

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Message-ID: <26c82c13-d047-853e-12af-e916596c5c52@synopsys.com>
Date:   Wed, 23 Mar 2022 01:31:00 +0000
From:   Thinh Nguyen <Thinh.Nguyen@...opsys.com>
To:     Wesley Cheng <wcheng@...eaurora.org>,
        Wesley Cheng <quic_wcheng@...cinc.com>,
        "balbi@...nel.org" <balbi@...nel.org>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
CC:     "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "quic_jackp@...cinc.com" <quic_jackp@...cinc.com>,
        Thinh Nguyen <Thinh.Nguyen@...opsys.com>
Subject: Re: [RFC PATCH v2 1/3] usb: dwc3: Flush pending SETUP data during
 stop active xfers

Hi Wesley,

Wesley Cheng wrote:
> Hi Thinh,
> 
> On 2/15/2022 4:08 PM, Wesley Cheng wrote:
>> While running the pullup disable sequence, if there are pending SETUP
>> transfers stored in the controller, then the ENDTRANSFER commands on non
>> control eps will fail w/ ETIMEDOUT.  As a suggestion from SNPS, in order
>> to drain potentially cached SETUP packets, SW needs to issue a
>> STARTTRANSFER command.  After issuing the STARTTRANSFER, and retrying the
>> ENDTRANSFER, the command should succeed.  Else, if the endpoints are not
>> properly stopped, the controller halt sequence will fail as well.
>>
>> One limitation is that the current logic will drop the SETUP data
>> being received (ie dropping the SETUP packet), however, it should be
>> acceptable in the pullup disable case, as the device is eventually
>> going to disconnect from the host.
>>
>> Signed-off-by: Wesley Cheng <quic_wcheng@...cinc.com>
>> ---
> Just wondering if you had any inputs for this particular change?  I
> think on the dequeue path discussion you had some concerns with parts of
> this change?  I think the difficult part for the pullup disable path is
> that we have this API running w/ interrupts disabled, so the EP0 state
> won't be able to advance compared to the dequeue case.

This doesn't sound right. The pullup disable (or device initiated
disconnect) should wait for the EP0 state to be EP0_SETUP_PHASE before
proceeding, which it does.

> 
> Ideally, if there is a way to ensure that we avoid reading further setup
> packets, that would be nice, but from our discussions with Synopsys,
> this was not possible. (controller is always armed and ready to ACK
> setup tokens)
> 
> I did evaluate keeping IRQs enabled and periodically releasing/attaining
> the lock between the stop active xfer calls, but that opened another can
> of worms.  If you think this is the approach we should take, I can take
> a look at this implementation further.
> 

This patch doesn't look right to me. The change I suggested before
should address this (I believe Greg already picked it up). What other
problem do you see, I'm not clear what's the problem here. One potential
problem that I can see is that currently dwc3 driver doesn't wait for
active endpoints to complete/end before clearing the run_stop bit on
device initiated disconnect, but I'm not sure if that's what you're seeing.

Please help clarify further. If there's trace points log, that'd help.

Thanks,
Thinh