UVC gadget on imx8mevk

[hanyi]

Hello community,

We're trying to get UVC gadget working on imx8m-evk, without any success.

The system is initialized using "repo init -u https://source.codeaurora.org/external/imx/imx-manifest -b imx-linux-sumo -m imx-4.14.98-2.0.0_ga.xml"

1. mipi cameras are verified using gstreamer
2. usb gadget's configured with configfs:  mkdir /sys/kernel/config/usb_gadget/g1
   cd /sys/kernel/config/usb_gadget/g1
   mkdir configs/c.1
   mkdir strings/0x409
   mkdir configs/c.1/strings/0x409
   echo 0x3290 > idProduct
   echo 0x18ec > idVendor
   echo 0x0310 > bcdUSB
   echo serial > strings/0x409/serialnumber
   echo manufacturer > strings/0x409/manufacturer
   echo UVC Gadget > strings/0x409/product
   echo "Conf 1" > configs/c.1/strings/0x409/configuration
   echo 120 > configs/c.1/MaxPower
   mkdir functions/uvc.usb0
   mkdir -p functions/uvc.usb0/streaming/uncompressed/u/480p
   cat <<EOF > functions/uvc.usb0/streaming/uncompressed/u/480p/dwFrameInterval
   333333
   1000000
   5000000
   EOF
   echo 480 > functions/uvc.usb0/streaming/uncompressed/u/480p/wHeight
   echo 333333 > functions/uvc.usb0/streaming/uncompressed/u/480p/dwDefaultFrameInterval
   echo 614400 > functions/uvc.usb0/streaming/uncompressed/u/480p/dwMaxVideoFrameBufferSize
   echo 73728000 > functions/uvc.usb0/streaming/uncompressed/u/480p/dwMaxBitRate
   echo 24576000 > functions/uvc.usb0/streaming/uncompressed/u/480p/dwMinBitRate
   mkdir functions/uvc.usb0/streaming/header/h
   cd functions/uvc.usb0/streaming/header/h
   ln -s ../../uncompressed/u
   cd ../../class/fs
   ln -s ../../header/h
   cd ../../class/hs
   ln -s ../../header/h
   cd ../../class/ss
   ln -s ../../header/h
   cd ../../../control
   mkdir header/h
   ln -s header/h class/fs
   ln -s header/h class/hs
   ln -s header/h class/ss
   cd /sys/kernel/config/usb_gadget/g1
   echo 1024 > functions/uvc.usb0/streaming_maxpacket
   echo 15 > functions/uvc.usb0/streaming_maxburst
   ln -s functions/uvc.usb0 configs/c.1
   echo 38100000.dwc3 > UDC
3. After running user space testing app(https://github.com/wlhe/uvc-gadget, with changes from 640x360 to 640x480 to match supported formats in ov5640_mipi_v2.c), imx8m-evk can be detected as a uvc device.

However, once I opened the UVC with VLC player, there's no video streaming.

After further investigation, I discovered that UVC video payload packets were not sent out successfully by ISO endpoints, usb_request.complete was never called.

dwc3_send_gadget_ep_cmd(dwc3/gadget.c) returns -EAGAIN, indicating an error status of 'Bus Expiry'. Data flow is: dwc3_endpoint_interrupt() => dwc3_gadget_start_isoc() => __dwc3_gadget_kick_transfer() => dwc3_send_gadget_ep_cmd()

We're running out of lead,

any help or information would be appreciated.

[puttopolly]

I already fail on the step "mkdir functions/uvc.usb0":

> mkdir: cannot create directory 'uvc.usb0': Operation not permitted

I listed directory with gadget modules:

>>ls /lib/modules/4.14.98-imx_4.14.98_2.0.0_ga+g5d6cbea/kernel/drivers/usb/gadget/legacy

g_audio.ko g_ether.ko g_ncm.ko g_zero.ko
g_cdc.ko g_mass_storage.ko g_serial.ko

Don't I have required module in my image? I googled during 1 hour and couldn't find any answers, how to activate UVC gadget.

I tried modprobe uvcvideo and I have this module now, but it still not working. It seems to be another module.

[hanyi]

For people that running into the same problem, it seems to be a dwc3 usb controller(driver) problem.

There's another post about this from 2018, but I guess he didn't dig that deep:

Issue in Video Streaming with gadget webcam module g_webcam in i.MX8 EVK 

I've seen people having this problem on RK3399 which also integrate dwc3 as its usb controller.

firefly rk3399 uvc-gadget 无法正常工作 · Issue #167 · rockchip-linux/kernel · GitHub 

I hope in the future someone would be more committed to solving this, and this post would give him some useful information.

I'm currently done with this, not a big issue, I think most customer can accept not having uvc gadget feature.

After all no one cares about uvc gadget on a platform like imx8, it simply isn't designed for that purpose.

[CarlosCasillas]

Hi Han,
You could take a look to the following Community thread for reference information:

i.MX 6,7,8 support USB device mode support to UVC 

Also, on application note AN12103 is implemented a UVC, but based on a i.MX RT processor:

https://www.nxp.com/docs/en/application-note/AN12103.pdf 

Hope this will be useful for you.
Best regards!
/Carlos
-------------------------------------------------------------------------------
Note:
- If this post answers your question, please click the "Mark Correct" button. Thank you!

-------------------------------------------------------------------------------

[hanyi]

Thanks for you reply, Carlos.

But we know that isn't helping with this particular problem, no one's ever successfully verified UVC gadget on imx8 as far as I know.