The `ast` Linux DRM GPU driver is *extremely* slow at page flipping.

A simple test app which performs atomic commits on a 1080p display takes ~45ms per page flip.

The issue seems to be horrendously slow copying of framebuffers to VRAM.

![perf top](perf-fbdev.png)
![hotspot](hotspot-drm.png)

AST2500 cards appear to support DMA however the ast driver doesn't use it.

![ast2520a2gp_datasheet](ast2520a2gp_datasheet.png)

It may be possible to adapt [XDMA code in github:eddiejames/xdma-test](
https://github.com/eddiejames/xdma-test/blob/master/host/ast-bmc-pcie.c) for the `ast` GPU driver.  
I'll update this article if I get that working or fail to.