On Thu, Jul 04, 2024 at 02:40:16PM +0800, Icenowy Zheng wrote: > > Nothing in the PCIe specifications that mandates a programming model. > > Non-coherent DMA is extremely common in lower end devices, and > > despite > > all the issues that it causes well supported in Linux. > > > > What are you trying to solve? > > Currently the DRM TTM subsystem (and GPU drivers using it) will assume > coherency and fail on these non-coherent systems with cryptic error > messages (like `[drm:amdgpu_ring_test_helper [amdgpu]] *ERROR* ring gfx > test failed (-110)`) without mentioning coherency issues at all. > > My original patchset tries to solve this problem by make the TTM > subsystem sensible of coherency status (and prevent CPU-side cached > mapping when non-coherent), but got argued by TTM maintainer and the > maintainer says TTM's ignorance on non-coherent systems is intentional.
