linux-kernel - Re: [PATCH v2] usb: dwc3: gadget: Check for IOC/LST bit in TRB->ctrl fields

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Message-ID: <87imku8q8o.fsf@kernel.org>
Date:   Wed, 29 Jan 2020 13:19:03 +0200
From:   Felipe Balbi <balbi@...nel.org>
To:     John Stultz <john.stultz@...aro.org>
Cc:     lkml <linux-kernel@...r.kernel.org>,
        Anurag Kumar Vulisha <anurag.kumar.vulisha@...inx.com>,
        Yang Fei <fei.yang@...el.com>,
        Thinh Nguyen <thinhn@...opsys.com>,
        Tejas Joglekar <tejas.joglekar@...opsys.com>,
        Andrzej Pietrasiewicz <andrzej.p@...labora.com>,
        Jack Pham <jackp@...eaurora.org>, Todd Kjos <tkjos@...gle.com>,
        Greg KH <gregkh@...uxfoundation.org>,
        Linux USB List <linux-usb@...r.kernel.org>,
        stable <stable@...r.kernel.org>
Subject: Re: [PATCH v2] usb: dwc3: gadget: Check for IOC/LST bit in TRB->ctrl fields


Hi,

John Stultz <john.stultz@...aro.org> writes:
> On Tue, Jan 28, 2020 at 11:23 PM Felipe Balbi <balbi@...nel.org> wrote:
>> John Stultz <john.stultz@...aro.org> writes:
>> > From: Anurag Kumar Vulisha <anurag.kumar.vulisha@...inx.com>
>> >
>> > The current code in dwc3_gadget_ep_reclaim_completed_trb() will
>> > check for IOC/LST bit in the event->status and returns if
>> > IOC/LST bit is set. This logic doesn't work if multiple TRBs
>> > are queued per request and the IOC/LST bit is set on the last
>> > TRB of that request.
>> >
>> > Consider an example where a queued request has multiple queued
>> > TRBs and IOC/LST bit is set only for the last TRB. In this case,
>> > the core generates XferComplete/XferInProgress events only for
>> > the last TRB (since IOC/LST are set only for the last TRB). As
>> > per the logic in dwc3_gadget_ep_reclaim_completed_trb()
>> > event->status is checked for IOC/LST bit and returns on the
>> > first TRB. This leaves the remaining TRBs left unhandled.
>> >
>> > Similarly, if the gadget function enqueues an unaligned request
>> > with sglist already in it, it should fail the same way, since we
>> > will append another TRB to something that already uses more than
>> > one TRB.
>> >
>> > To aviod this, this patch changes the code to check for IOC/LST
>> > bits in TRB->ctrl instead.
>> >
>> > At a practical level, this patch resolves USB transfer stalls seen
>> > with adb on dwc3 based HiKey960 after functionfs gadget added
>> > scatter-gather support around v4.20.
>> >
>> > Cc: Felipe Balbi <balbi@...nel.org>
>> > Cc: Yang Fei <fei.yang@...el.com>
>> > Cc: Thinh Nguyen <thinhn@...opsys.com>
>> > Cc: Tejas Joglekar <tejas.joglekar@...opsys.com>
>> > Cc: Andrzej Pietrasiewicz <andrzej.p@...labora.com>
>> > Cc: Jack Pham <jackp@...eaurora.org>
>> > Cc: Todd Kjos <tkjos@...gle.com>
>> > Cc: Greg KH <gregkh@...uxfoundation.org>
>> > Cc: Linux USB List <linux-usb@...r.kernel.org>
>> > Cc: stable <stable@...r.kernel.org>
>> > Tested-by: Tejas Joglekar <tejas.joglekar@...opsys.com>
>> > Reviewed-by: Thinh Nguyen <thinhn@...opsys.com>
>> > Signed-off-by: Anurag Kumar Vulisha <anurag.kumar.vulisha@...inx.com>
>> > [jstultz: forward ported to mainline, reworded commit log, reworked
>> >  to only check trb->ctrl as suggested by Felipe]
>> > Signed-off-by: John Stultz <john.stultz@...aro.org>
>>
>> since v5.5 is already merged, I'll send this to Greg once -rc1 is
>> tagged. It's already in my testing/fixes branch waiting for a pull
>> request.
>
> Great, thanks so much for queueing this! I'll be digging on the db845c

no worries, it was way past the time :-)

> side wrt the dma-api issue to hopefully get that one sorted as well.

Thanks, that would, indeed, be great :-)

> Thanks again for the help and analysis!

no worries. If you find anything odd, just collect traces and I can help
have a look.

-- 
balbi

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