On 9/23/22 12:43, Thomas Zimmermann wrote: > Hi > > Am 23.09.22 um 10:06 schrieb Javier Martinez Canillas: >> On 9/22/22 15:09, Thomas Zimmermann wrote: >>> Synchronize CPU access to GEM BOs with other drivers when updating the >>> screen buffer. Imported buffers might otherwise contain stale data. >>> >> >> Can you please elaborate what the problem is? The framebuffers memory is >> setup by the firmware and would never come from an imported dma-buf, so >> could the GEM BOs even be shared with other drivers? >> >> Or is this done just for the sake of correctness ? > > This isn't about the scanout buffer that we get from the firmware. This > is about synchronizing access to the GEM BO memory buffers. Our BOs' > memory buffer are allocated from SHMEM or could be imported via dma-buf. > In the latter case, another driver or hardware might modify their > content concurrently. We need to synchronize before reading the memory > from our CPU. The pattern is > > 1) sync BO memory content via begin_cpu_access() > 2) blit from BO mem to scanout buffer > 3) release BO memory via end_cpu_access() > Yeah, I got that part. What I was asking is if importing from dma-buf is a real use case for simpledrm or if this patch was more about making the driver correct and aligned with what other DRM drivers do? In any case I agree with the change, it's just the rationale for it that wasn't clear to me. -- Best regards, Javier Martinez Canillas Core Platforms Red Hat
