[PATCH v3 0/4] drm/ast: Disable HW cursor when switching modes

[Thomas Zimmermann <tzimmermann@suse.de>]

Since converting the ast driver to atomic modesettting, 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 way, 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.

v3:
	* rewrote the patchset again
	* format setup is now done on primary-plane update
	* don't disable cursor for format changes (does not seem necessary)
	* disable planes in CRTC atomic_disable()
	* do modeset in atomic_enable()
	* drop Fixes tags; it's too complicated for a simple bugfix

v2:
	* rewrote the whole patchset
	* dropped the cursor patches
	* moved modesetting into atomic_begin()
	* disable planes in commit-tail function
	* don't require full modeset for format changes

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

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