linux-kernel - RE: [RFC][PATCH 0/2] Avoiding DWC3 transfer stalls/hangs when using adb over f

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Date:   Thu, 23 Jan 2020 17:37:14 +0000
From:   "Yang, Fei" <fei.yang@...el.com>
To:     Felipe Balbi <balbi@...nel.org>,
        Andrzej Pietrasiewicz <andrzej.p@...labora.com>,
        John Stultz <john.stultz@...aro.org>,
        lkml <linux-kernel@...r.kernel.org>
CC:     Felipe Balbi <felipe.balbi@...ux.intel.com>,
        Thinh Nguyen <thinhn@...opsys.com>,
        Tejas Joglekar <tejas.joglekar@...opsys.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: [RFC][PATCH 0/2] Avoiding DWC3 transfer stalls/hangs when using
 adb over f_fs

>>>> Hey all,
>>>>    I wanted to send these out for comment and thoughts.
>>>> 
>>>> Since ~4.20, when the functionfs gadget enabled scatter-gather 
>>>> support, we have seen problems with adb connections stalling and 
>>>> stopping to function on hardware with dwc3 usb controllers.
>>>> Specifically, HiKey960, Dragonboard 845c, and Pixel3 devices.
>>>
>>> Any chance this:
>>> 
>>> https://git.kernel.org/pub/scm/linux/kernel/git/balbi/usb.git/commit/
>>> ?h=testing/next&id=f63333e8e4fd63d8d8ae83b89d2c38cf21d64801
>> This is a different issue. I have tried initializing num_sgs when debugging this adb stall problem, but it didn't help.
>
> So multiple folks have run through this problem, but not *one* has tracepoints collected from the issue? C'mon guys. Can someone, please, collect tracepoints so we can figure out what's actually going on?
>
> I'm pretty sure this should be solved at the DMA API level, just want to confirm.
I have sent you the tracepoints long time ago. Also my analysis of the problem (BTW, I don't think the tracepoints helped much). It's basically a logic problem in function dwc3_gadget_ep_reclaim_trb_sg().
I can try dig into my old emails and resend, but that is a bit hard to find.

-Fei