Le lundi 15 février 2021 à 09:58 +0100, Christian König a écrit :
Hi guys,
we are currently working an Freesync and direct scan out from system memory on AMD APUs in A+A laptops.
On problem we stumbled over is that our display hardware needs to scan out from uncached system memory and we currently don't have a way to communicate that through DMA-buf.
For our specific use case at hand we are going to implement something driver specific, but the question is should we have something more generic for this?
Hopefully I'm getting this right, but this makes me think of a long standing issue I've met with Intel DRM and UVC driver. If I let the UVC driver allocate the buffer, and import the resulting DMABuf (cacheable memory written with a cpu copy in the kernel) into DRM, we can see cache artifact being displayed. While if I use the DRM driver memory (dumb buffer in that case) it's clean because there is a driver specific solution to that.
There is no obvious way for userspace application to know what's is right/wrong way and in fact it feels like the kernel could solve this somehow without having to inform userspace (perhaps).
After all the system memory access pattern is a PCIe extension and as such something generic.
Regards, Christian.