[Intel-gfx] [PATCH] drm/i915: Wait for vblank before enabling the TV encoder

[ville.syrjala at linux.intel.com]

From: Ville Syrjälä <ville.syrjala at linux.intel.com>

The vblank waits in intel_tv_detect_type() are timing out for some
reason. This is a regression caused removing seemingly useless vblank
waits from the modeset seqeuence in:

 commit 56ef52cad5e37fca89638e4bad598a994ecc3d9f
 Author: Ville Syrjälä <ville.syrjala at linux.intel.com>
 Date:   Thu May 8 19:23:15 2014 +0300

    drm/i915: Kill vblank waits after pipe enable on gmch platforms

So it turns out they weren't all entirely useless. Apparently the pipe
has to go through one full frame before we enable the TV port. Add a
vblank wait to intel_enable_tv() to make sure that happens.

Another approach was attempted by placing the vblank wait just after
enabling the port. The theory behind that attempt was that we need to
let the port stay enabled for one full frame before disabling it again
during load detection. But that didn't work, and we definitely must
have the vblank wait before enabling the port.

Cc: stable at vger.kernel.org
Cc: Alan Bartlett <ajb at elrepo.org>
Tested-by: Alan Bartlett <ajb at elrepo.org>
Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=79311
Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
---
 drivers/gpu/drm/i915/intel_tv.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/gpu/drm/i915/intel_tv.c b/drivers/gpu/drm/i915/intel_tv.c
index c69d3ce..c14341c 100644
--- a/drivers/gpu/drm/i915/intel_tv.c
+++ b/drivers/gpu/drm/i915/intel_tv.c
@@ -854,6 +854,10 @@ intel_enable_tv(struct intel_encoder *encoder)
 	struct drm_device *dev = encoder->base.dev;
 	struct drm_i915_private *dev_priv = dev->dev_private;
 
+	/* Prevents vblank waits from timing out in intel_tv_detect_type() */
+	intel_wait_for_vblank(encoder->base.dev,
+			      to_intel_crtc(encoder->base.crtc)->pipe);
+
 	I915_WRITE(TV_CTL, I915_READ(TV_CTL) | TV_ENC_ENABLE);
 }
 
-- 
1.8.5.5