Faster display presentation with Video DMA

2026-09-06 - Faster display presentation with Video DMA

The graphics driver now supports the Video DMA (VDMA) engine, which can convert color format as it copies. The display only accepts 32-bit color, so until now the whole desktop had to be drawn in 32-bit and the 2D engine had to copy every finished frame to the display on top of its own drawing. The desktop is now drawn in 16-bit color, halving the memory each pixel takes, and the VDMA carries what changed to the display in 32-bit while the 2D engine only draws. The VDMA moves a full frame in about half the time the 2D engine took, and drawing in 16-bit makes no discernible difference on screen.
The X.org driver now draws the desktop in 16-bit color and hands what changed on screen to the VDMA to put on the display, presenting through that same path with TearFree on or off and with or without 2D acceleration.
Halving the pixel footprint and freeing the 2D engine from presentation copies makes drawing faster across the board. Large fills and copies are now roughly double in speed, window blits (moving and scrolling) improve by over half, and the X server uses between a quarter and three quarters less CPU per operation.
Page flips no longer wait on a deadline. Before, the kernel waited up to 100 ms for the 2D engine to finish writing a newly drawn frame and then displayed it anyway, which under heavy load could show a partially drawn frame. Now a flip always waits for the 2D engine to finish before the frame is shown.
IceWM has been patched to fix menu icons disappearing at 16-bit color depth when only part of a window was redrawn.
The kernel now ignores the SD card's lock switch. A board that reads every card as write-protected (issue #21) could not boot, since the root filesystem lives on the card and has to be writable.
Further cleanup of the display driver and the X.org driver, with nothing that changes in everyday use.
Kernel updated to 6.12.108.
Refreshed standard and desktop images.