[PATCH v2 0/3] uvc gadget performance issues

[Dan Vacura]

Hello uvc gadget developers,

Please find my V2 series with added patches to disable these performance
features at the userspace level for devices that don't work well with
the UDC hw, i.e. dwc3 in this case. Also included are updates to
comments for the v1 patch.

Original note:

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:

https://patchwork.kernel.org/project/linux-usb/patch/20210628155311.16762-5-m.grzeschik@xxxxxxxxxxxxxx/  and 
https://patchwork.kernel.org/project/linux-usb/patch/20210628155311.16762-6-m.grzeschik@xxxxxxxxxxxxxx/

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|
    +-------------------------+


Dan Vacura (3):
  usb: gadget: uvc: make interrupt skip logic configurable
  usb: gadget: uvc: fix sg handling in error case
  usb: gadget: uvc: add configfs option for sg support

 .../ABI/testing/configfs-usb-gadget-uvc       |  2 ++
 Documentation/usb/gadget-testing.rst          |  4 ++++
 drivers/usb/gadget/function/f_uvc.c           |  5 +++++
 drivers/usb/gadget/function/u_uvc.h           |  2 ++
 drivers/usb/gadget/function/uvc.h             |  1 +
 drivers/usb/gadget/function/uvc_configfs.c    |  4 ++++
 drivers/usb/gadget/function/uvc_queue.c       | 18 +++++++++++-----
 drivers/usb/gadget/function/uvc_video.c       | 21 ++++++++++++++-----
 8 files changed, 47 insertions(+), 10 deletions(-)

-- 
2.34.1