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.
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? 😁
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.
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!