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

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.


Dan Vacura (1):
usb: gadget: uvc: fix sg handling in error case

drivers/usb/gadget/function/uvc_queue.c | 8 +++++---
drivers/usb/gadget/function/uvc_queue.h | 2 +-
drivers/usb/gadget/function/uvc_video.c | 18 ++++++++++++++----
3 files changed, 20 insertions(+), 8 deletions(-)

--
2.20.4

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