linux-kernel - Re: [RFC][PATCH 1/2] usb: dwc3: gadget: Check for IOC/LST bit in both event->status and TRB->ctrl fields

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Date:   Thu, 23 Jan 2020 09:24:17 +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: [RFC][PATCH 1/2] usb: dwc3: gadget: Check for IOC/LST bit in both event->status and TRB->ctrl fields


Hi,

John Stultz <john.stultz@...aro.org> writes:

> 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
     avoid

> event->status & TRB->ctrl. This patch does the same.

We don't need to check both. It's very likely that checking the TRB is
enough.

> 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.

Right, I remember asking for tracepoint data showing this problem
happening. It's the best way to figure out what's really going on.

Before we accept these two patches, could you collect dwc3 tracepoint
data and share here?

-- 
balbi

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