[dividuum]

In general DRM/KMS can be quite confusing a there seems little userland documentation available. I assume you get the DMA buffers from the HDMI input somehow? If so, you should be able to use drmModeAddFB2WithModifiers to create a DRM framebuffer from them. Then attach that to a DRM plane, place that on a CRTC and then schedule a page flip after modesetting a video mode.

The advantage would be that you can directly run without starting into any kind of visual environment first. But it's a huge mess to get going: I wrote quite a bit of Pi4/5 code recently to make a zero copy HEVC/H264 decoder working and it was a quite a challenge. Maybe code like https://github.com/dvdhrm/docs/tree/master/drm-howto can help?

[benhoff]

The HDMI receive device on the OrangePi5 plus is in a semi-functional state. Collabora is in the process of up-streaming code so the RK3588 will work with the mainline linux kernel.

Until that happens, working driver code is in a very transitive space.

To get going, and sidestep that problem, I've purchased an HDMI to USB capture cards that use MacroSilicon chips. I've some thought of using a cheaper CPU in the future with a daughter board based on this project which uses MacoSilicon chips: https://github.com/YuzukiHD/YuzukiLOHCC-PRO, which made it potentially not a waste of time to dig into.

The MacroSilicon HDMI to USB capture cards output MJEPG, which Rockchip's MPP library has decoder for.

So the thought is: (1) allocate a DMA buffer (2) set that DMA buffer as the MJEPG decoder target (3) get the decoded data to display (sounds like I may need to encode again?) & a parallel processing pipeline

I'll dig into the stuff you've sent over, very helpful thanks for the pointers!

I've thought about switching to Pi4/5 for this. Based on your experience, would you recommend that platform?

[dividuum]

> I've thought about switching to Pi4/5 for this. Based on your experience, would you recommend that platform?

Their kernel fork is well maintained and if there is a reproducible problem it usually gets fixed quite quickly. Overall pretty happy. KMS/DRM was a bit wonky as there was a transition phase where they used a hacky mix between KMS and the old proprietary broadcom APIs (FakeKMS). But those days are over and so far KMS/DRM works pretty well for what I'm using it.