[PATCH 1/4] drm/vc4: Allow vblank_disable_immediate on non-fw-kms.

[Mario Kleiner]

With instantaneous high precision vblank timestamping
that updates at leading edge of vblank, the emulated
"hw vblank counter" from vblank timestamping 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
vblank irq disable/enable.

Testing against rpi-4.12-rc5 Linux kernel 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
would keep vblank irqs on to approximate old behavior.

Signed-off-by: Mario Kleiner <mario.kleiner.de at gmail.com>
Cc: Eric Anholt <eric at anholt.net>
---
 drivers/gpu/drm/vc4/vc4_kms.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/gpu/drm/vc4/vc4_kms.c b/drivers/gpu/drm/vc4/vc4_kms.c
index 928d191..70c4e17 100644
--- a/drivers/gpu/drm/vc4/vc4_kms.c
+++ b/drivers/gpu/drm/vc4/vc4_kms.c
@@ -216,6 +216,10 @@ int vc4_kms_load(struct drm_device *dev)
 
 	sema_init(&vc4->async_modeset, 1);
 
+	/* Set support for vblank irq fast disable, before drm_vblank_init() */
+	if (!vc4->firmware_kms)
+		dev->vblank_disable_immediate = true;
+
 	ret = drm_vblank_init(dev, dev->mode_config.num_crtc);
 	if (ret < 0) {
 		dev_err(dev->dev, "failed to initialize vblank\n");
-- 
2.7.4