So I finally understand why 4-lane MIPI CSI-2 doesn't work with the #Librem5's big cam.
Turns out it's not going to work - but I now at least understand why 😂
(this limits streaming at full res to about 16 FPS 10-bit and 20 FPS 8-bit instead of the sensor's 30 FPS, but you won't really be able to process it at this speed anyway so it's not a big loss; lower res can still work with higher framerates; with the current driver up to 120 FPS but it could go even higher)
Actually, we could probably go up to 21 FPS with 10-bit by using 3 lanes, but not sure if that's worth the effort.
It doesn't look particularly useful for the use-case of streaming through USB 3.0 either.
With 2 lanes, at 4K we get 30 FPS with 8-bit and 25 FPS with 10-bit.
8-bit may fit into available USB 3.0 bandwidth, though it's already getting tight. 10-bit won't fit without repacking, cause we're getting 16-bit values from the CSI receiver - so you likely won't stream out more than 15 FPS anyway.
So 2 lanes it is!
We'll eventually want that capability, and someone has to be first.
@pavel You can already get 10-bit 25 FPS without having to put extra plumbing between kernel drivers for questionable reward.
This would translate to about 33 FPS when cropped to 4K.
We should be able to record up to 5 seconds of 10-bit 4K 30 FPS video to RAM, assuming 2GB of free space there. Is that worth the effort? 😁