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

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Date:   Wed, 29 Jan 2020 09:16:19 +0200
From:   Felipe Balbi <balbi@...nel.org>
To:     Thinh Nguyen <Thinh.Nguyen@...opsys.com>,
        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>,
        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,

Thinh Nguyen <Thinh.Nguyen@...opsys.com> writes:
>> 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 :-)
>
> Just a note: right now, it may be fine for non-stream endpoints to not 
> set the LST bit in the TRBs. For streams, we need to set this bit so the 
> controller know to allocate resource for different transfers of 
> different streams. It may be fine now if you think that it should be 
> added later when more fixes for streams are added, but I think it 
> doesn't hurt checking it now either.

Indeed. Let's keep this version as is if we will need LST for Streams
anyway. Sorry for the noise.

-- 
balbi

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