linux-kernel - Re: [PATCH] usb: dwc3: Check for IOC/LST bit in both event->status and TRB->ctrl fields

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Date:   Mon, 29 Jul 2019 11:34:10 -0700
From:   John Stultz <john.stultz@...aro.org>
To:     lkml <linux-kernel@...r.kernel.org>
Cc:     Anurag Kumar Vulisha <anurag.kumar.vulisha@...inx.com>,
        Felipe Balbi <felipe.balbi@...ux.intel.com>,
        Fei Yang <fei.yang@...el.com>,
        Thinh Nguyen <thinhn@...opsys.com>,
        Tejas Joglekar <tejas.joglekar@...opsys.com>,
        Andrzej Pietrasiewicz <andrzej.p@...labora.com>,
        Greg KH <gregkh@...uxfoundation.org>,
        Linux USB List <linux-usb@...r.kernel.org>,
        stable <stable@...r.kernel.org>
Subject: Re: [PATCH] usb: dwc3: Check for IOC/LST bit in both event->status
 and TRB->ctrl fields

On Tue, Jul 23, 2019 at 1:27 PM John Stultz <john.stultz@...aro.org> wrote:
>
> From: Anurag Kumar Vulisha <anurag.kumar.vulisha@...inx.com>
>
> The present 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 makes the remaining
> TRBs left unhandled.
> To aviod this, changed the code to check for IOC/LST bits in both
> event->status & TRB->ctrl. This patch does the same.
>
> At a practical level, this patch resolves USB transfer stalls seen
> with adb on dwc3 based Android devices after functionfs gadget
> added scatter-gather support around v4.20.
>
> Cc: Felipe Balbi <felipe.balbi@...ux.intel.com>
> Cc: Fei Yang <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: 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, added note to commit log]
> Signed-off-by: John Stultz <john.stultz@...aro.org>
> ---
> Just wanted to send this out so we're all looking at the same thing.
> Not sure if its correct, but it seems to solve the adb stalls I've
> been seeing for awhile.

Felipe: Any thoughts on this patch?

thanks
-john