[PATCH 3/4] drm/amdgpu: Allow vblank_disable_immediate.

[Mario Kleiner]

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 R9 380
Tonga Pro (DCE 10) 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.

Signed-off-by: Mario Kleiner <mario.kleiner.de at gmail.com>
Cc: Alex Deucher <alexander.deucher at amd.com>
Cc: Michel Dänzer <michel.daenzer at amd.com>
---
 drivers/gpu/drm/amd/amdgpu/amdgpu_irq.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_irq.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_irq.c
index 62da6c5..a28f8aa 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_irq.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_irq.c
@@ -220,6 +220,10 @@ int amdgpu_irq_init(struct amdgpu_device *adev)
 	int r = 0;
 
 	spin_lock_init(&adev->irq.lock);
+
+	/* Disable vblank irqs aggressively for power-saving */
+	adev->ddev->vblank_disable_immediate = true;
+
 	r = drm_vblank_init(adev->ddev, adev->mode_info.num_crtc);
 	if (r) {
 		return r;
-- 
2.7.4