drm/radeon: Allow vblank_disable_immediate.
authorMario Kleiner <mario.kleiner.de@gmail.com>
Wed, 21 Jun 2017 01:44:55 +0000 (03:44 +0200)
committerAlex Deucher <alexander.deucher@amd.com>
Fri, 14 Jul 2017 15:05:51 +0000 (11:05 -0400)
commit08d3874636a20b8852f8eea1c6ad1054234c9ae6
tree6d5f1480d2c92157648e9625fbe495e4611da5a1
parente4f6b39e8bcd1f4c455acbc1aef2de9a4a32deeb
drm/radeon: Allow vblank_disable_immediate.

With instantaneous high precision vblank timestamping
that updates at leading edge of vblank, a cooked hw
vblank counter which increments at leading edge of
vblank, and reliable page flip execution and completion
at leading edge of vblank, we should meet the requirements
for fast/immediate vblank irq disable/enable.

Testing on Linux-4.12-rc5 + drm-next on a Radeon HD 5770
(DCE 4) with timing measurement equipment indicates this
works fine, so allow immediate vblank disable for power
saving.

For debugging in case of unexpected trouble, booting
with kernel cmdline option drm.vblankoffdelay=0
(or echo 0 > /sys/module/drm/parameters/vblankoffdelay)
would keep vblank irqs permanently on to approximate old
behavior.

Reviewed-and-Tested-by: Michel Dänzer <michel.daenzer@amd.com>
Signed-off-by: Mario Kleiner <mario.kleiner.de@gmail.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: Michel Dänzer <michel.daenzer@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
drivers/gpu/drm/radeon/radeon_irq_kms.c