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

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Message-ID: <87sgjz90lt.fsf@kernel.org>
Date:   Tue, 28 Jan 2020 15:22:54 +0200
From:   Felipe Balbi <balbi@...nel.org>
To:     John Stultz <john.stultz@...aro.org>,
        lkml <linux-kernel@...r.kernel.org>
Cc:     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>,
        John Stultz <john.stultz@...aro.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:

> 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>
> ---
> v2:
> * Rework to only check trb->ctrl as suggested by Felipe
> * Reword the commit message to include more of Felipe's assessment
> ---
>  drivers/usb/dwc3/gadget.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
> index 154f3f3e8cff..9a085eee1ae3 100644
> --- a/drivers/usb/dwc3/gadget.c
> +++ b/drivers/usb/dwc3/gadget.c
> @@ -2420,7 +2420,8 @@ static int dwc3_gadget_ep_reclaim_completed_trb(struct dwc3_ep *dep,
>  	if (event->status & DEPEVT_STATUS_SHORT && !chain)
>  		return 1;
>  
> -	if (event->status & DEPEVT_STATUS_IOC)
> +	if ((trb->ctrl & DWC3_TRB_CTRL_IOC) ||
> +	    (trb->ctrl & DWC3_TRB_CTRL_LST))

why the LST bit here? It wasn't there before. In fact, we never set LST
in dwc3 anymore :-)

-- 
balbi

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