Since converting the ast driver to atomic modesetting, modesetting occationally locks up the graphics hardware and turns the display permanently dark. This happens once or twice per 10 mode switches. Investigation shows that the ast hardware presumably requires the HW cursor to be disabled while the modeswitch takes place.
This patchset fixes the problem by disabling planes before programming the CRTC mode. After the switch, the planes gets re-enabled if they were enabled before. For mere pageflip operations, nothing changes.
Patches #1 makes format changes work as intended: format registers are only updated if necessary. They used to be changed on each pageflip.
Patches #2 to #4 change the modesetting logic such that planes will be disabled with the CRTC, then the CRTC's new mode is being programmed, and finally planes are reenabled. The primary plane is enabled before the cursor plane. With this setup, the cursor plane always has a valid mode and framebuffer available.
Tested on AST2100 HW. The issue is not 100% reproducible, but does not show up after applying the patchset. I think the problem has been fixed.
Thomas Zimmermann (4): drm/ast: Set format registers in primary plane's update drm/ast: Disable planes while switching display modes drm/ast: Program display mode in CRTC's atomic_enable() drm/ast: Enable CRTC before planes
drivers/gpu/drm/ast/ast_drv.h | 2 + drivers/gpu/drm/ast/ast_mode.c | 103 ++++++++++++++++++++------------- 2 files changed, 64 insertions(+), 41 deletions(-)
-- 2.28.0