Re: [PATCH 0/1] uvc gadget sg performance issues

[Michael Grzeschik <mgr@pengutronix.de>]

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Hi Dan!

On Mon, Sep 26, 2022 at 02:53:06PM -0500, Dan Vacura wrote:
>
>Hello uvc gadget developers,
>
>I'm working on a 5.15.41 based kernel on a qcom chipset with the dwc3
>controller and I'm encountering two problems related to the recent performance
>improvement changes:

What's about that odd kernel number. UVC is under heavy development, if
you plan to work with this code, you should probably test top of tree.

>https://patchwork.kernel.org/project/linux-usb/patch/20210628155311.16762-5-m.grzeschik@pengutronix.de/  and
>https://patchwork.kernel.org/project/linux-usb/patch/20210628155311.16762-6-m.grzeschik@pengutronix.de/
>
>If I revert these two changes, then I have much improved stability and a
>transmission problem I'm seeing is gone. Has there been any success from
>others on 5.15 with this uvc improvement and any recommendations for my
>current problems?  Those being:
>
>1) a smmu panic, snippet here: 
>
>    <3>[  718.314900][  T803] arm-smmu 15000000.apps-smmu: Unhandled arm-smmu context fault from a600000.dwc3!
>    <3>[  718.314994][  T803] arm-smmu 15000000.apps-smmu: FAR    = 0x00000000efe60800
>    <3>[  718.315023][  T803] arm-smmu 15000000.apps-smmu: PAR    = 0x0000000000000000
>    <3>[  718.315048][  T803] arm-smmu 15000000.apps-smmu: FSR    = 0x40000402 [TF R SS ]
>    <3>[  718.315074][  T803] arm-smmu 15000000.apps-smmu: FSYNR0    = 0x5f0003
>    <3>[  718.315096][  T803] arm-smmu 15000000.apps-smmu: FSYNR1    = 0xaa02
>    <3>[  718.315117][  T803] arm-smmu 15000000.apps-smmu: context bank#    = 0x1b
>    <3>[  718.315141][  T803] arm-smmu 15000000.apps-smmu: TTBR0  = 0x001b0000c2a92000
>    <3>[  718.315165][  T803] arm-smmu 15000000.apps-smmu: TTBR1  = 0x001b000000000000
>    <3>[  718.315192][  T803] arm-smmu 15000000.apps-smmu: SCTLR  = 0x0a5f00e7 ACTLR  = 0x00000003
>    <3>[  718.315245][  T803] arm-smmu 15000000.apps-smmu: CBAR  = 0x0001f300
>    <3>[  718.315274][  T803] arm-smmu 15000000.apps-smmu: MAIR0   = 0xf404ff44 MAIR1   = 0x0000efe4
>    <3>[  718.315297][  T803] arm-smmu 15000000.apps-smmu: SID = 0x40
>    <3>[  718.315318][  T803] arm-smmu 15000000.apps-smmu: Client info: BID=0x5, PID=0xa, MID=0x2
>    <3>[  718.315377][  T803] arm-smmu 15000000.apps-smmu: soft iova-to-phys=0x0000000000000000
>
>    I can reduce this panic with the proposed patch, but it still happens until I
>    disable the "req->no_interrupt = 1" logic.
>
>2) The frame is not fully transmitted in dwc3 with sg support enabled.
>
>    There seems to be a mapping limit I'm seeing where only the roughly first
>    70% of the total frame is sent. Interestingly, if I allocate a larger
>    size for the buffer upfront, in uvc_queue_setup(), like sizes[0] =
>    video->imagesize * 3. Then the issue rarely happens. For example, when I
>    do YUYV I see green, uninitialized data, at the bottom part of the
>    frame. If I do MJPG with smaller filled sizes, the transmission is fine.
>
>    +-------------------------+
>    |                         |
>    |                         |
>    |                         |
>    |      Good data          |
>    |                         |
>    |                         |
>    |                         |
>    +-------------------------+
>    |xxxxxxxxxxxxxxxxxxxxxxxxx|
>    |xxxx  Bad data  xxxxxxxxx|
>    |xxxxxxxxxxxxxxxxxxxxxxxxx|
>    +-------------------------+
>
>
>Appreciate any thoughts or feedback related to these issues.

Anyway, this is probably due to the frames being given back to early to
the frameproducer. We have the following patches mainline now to fix this issue:

aef11279888c00e1841a3533a35d279285af3a51 usb: gadget: uvc: improve sg exit condition
9b969f93bcef9b3d9e92f1810e22bbd6c344a0e5 usb: gadget: uvc: giveback vb2 buffer on req complete

You might need some patches beforehand to get them applied on your
stack.

Regards,
Michael

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