[PATCH 2/4] drm/radeon: 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 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.

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/radeon/radeon_irq_kms.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/gpu/drm/radeon/radeon_irq_kms.c b/drivers/gpu/drm/radeon/radeon_irq_kms.c
index 7aacb44..1860764 100644
--- a/drivers/gpu/drm/radeon/radeon_irq_kms.c
+++ b/drivers/gpu/drm/radeon/radeon_irq_kms.c
@@ -283,6 +283,10 @@ int radeon_irq_kms_init(struct radeon_device *rdev)
 	int r = 0;
 
 	spin_lock_init(&rdev->irq.lock);
+
+	/* Disable vblank irqs aggressively for power-saving */
+	rdev->ddev->vblank_disable_immediate = true;
+
 	r = drm_vblank_init(rdev->ddev, rdev->num_crtc);
 	if (r) {
 		return r;
-- 
2.7.4