Date: Thu, 9 Jun 2022 21:04:37 +0200 From: Alexander Graf agraf@csgraf.de
On 07.06.22 10:28, Heinrich Schuchardt wrote:
On 6/7/22 01:43, Alexander Graf wrote:
This patch set speeds up graphics output on ARM by a factor of 60x.
On most ARM SBCs, we keep the frame buffer in DRAM and map it as cached, but need it accessible by the display controller which reads directly from a later point of consistency. Hence, we flush the frame buffer to DRAM on every change. The full frame buffer.
Isn't a similar problem already solved by CONFIG_VIDEO_COPY?
Leaving the frame buffer uncached would convert the ARM problem into the X86 case?
It solves a similar problem, yes. However, it requires us to allocate the frame buffer size twice, and we would need to dynamically toggle the MMU mappings of the frame buffer to WC instead of cached. That's code we don't have today.
For the Apple M1 the framebuffer is covered by the "memory map" and maps it as Normal-NC, but that is because the framebuffer is already set up at the point where u-boot takes control.