Gstreamer / V4L support for MIPI CSI transmitter device

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Gstreamer / V4L support for MIPI CSI transmitter device


I'm writing a Linux driver for a MIPI CSI transmitter device. This
hardware allows the Linux system to transmit a MIPI CSI stream to a
suitable MIPI CSI receiver i.e. Linux behaves like a camera.
So far I have added a V4L output driver for the hardware and I am able
to transmit a video stream. To do this I am using gstreamer with v4l2sink:

gst-launch-1.0 videotestsrc  !
video/x-bayer,width=640,height=480,format=bggr ! v4l2sink device=/dev/video0

The issue is that the MIPI CSI transmitter needs to know the video
timings (pixelclock & blanking periods) that it should drive to the MIPI
CSI bus. For now, I just hardcoded 640x480@60fps numbers into the driver.
Ideally, I think I need to add support for DV_TIMINGS ioctls such that
userspace can enumerate the possible video timings (probably just a
subset of v4l2_dv_timings_presets)

I would then need to add support to Gstreamer's v4l2sink to get the
dv_timings, if supported, pick one compatible with the video caps, and
set it, along with the pixel format.

Is this the best approach? Are there any gotchas in this or other things
I should consider doing instead? One possibility is that I should
instead make the driver in the DRM subsystem. I didn't initially do that
do to missing support for the more exotic pixel formats that MIPI CSI
has e.g. raw bayer. But of course, DRM would give me much easier access
to video timings...

Thanks for any advice.
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