Hi! It seems that DMA-BUFs are always uncached on arm64... which is a problem.
I'm trying to get useful camera support on Librem 5, and that includes recording vidos (and taking photos). memcpy() from normal memory is about 2msec/1MB. Unfortunately, for DMA-BUFs it is 20msec/1MB, and that basically means I can't easily do 760p video recording. Plus, copying full-resolution photo buffer takes more than 200msec! There's possibility to do some processing on GPU, and its implemented here: https://gitlab.com/tui/tui/-/tree/master/icam?ref_type=heads but that hits the same problem in the end -- data is in DMA-BUF, uncached, and takes way too long to copy out. And that's ... wrong. DMA ended seconds ago, complete cache flush would be way cheaper than copying single frame out, and I still have to deal with uncached frames. So I have two questions: 1) Is my analysis correct that, no matter how I get frame from v4l and process it on GPU, I'll have to copy it from uncached memory in the end? 2) Does anyone have patches / ideas / roadmap how to solve that? It makes GPU unusable for computing, and camera basically unusable for video. Best regards, Pavel -- I don't work for Nazis and criminals, and neither should you. Boycott Putin, Trump, and Musk!
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