[PATCH 2/2] drm/i915: make sure we write at least 32 DIP bytes

[Paulo Zanoni <przanoni@gmail.com>]

From: Paulo Zanoni <paulo.r.zanoni@intel.com>

If we don't write at least 32 DIP bytes the InfoFrame ECC may not be
correctly calculated in some cases (e.g., when changing the port), and
this will lead to black screens on HDMI monitors. The ECC value is
generated by the hardware.

I don't see how this should break anything since we're writing 0 and
that should be the correct value, so this patch should be safe.

This patch fixes bug #46761, which is marked as a regression
introduced by commit 4e89ee174bb2da341bf90a84321c7008a3c9210d:
    drm/i915: set the DIP port on ibx_write_infoframe

Before commit 4e89 we were just failing to send AVI infoframes when we
needed to change the port, which can lead to black screens in some
cases. After commit 4e89 we started sending infoframes, but with a
possibly wrong ECC value. After this patch I hope we start sending
correct infoframes.

Cc: stable@vger.kernel.org
Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=46761
Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
---
 drivers/gpu/drm/i915/intel_hdmi.c |   10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/drivers/gpu/drm/i915/intel_hdmi.c b/drivers/gpu/drm/i915/intel_hdmi.c
index f9fb47c..4ca355e 100644
--- a/drivers/gpu/drm/i915/intel_hdmi.c
+++ b/drivers/gpu/drm/i915/intel_hdmi.c
@@ -151,6 +151,8 @@ static void g4x_write_infoframe(struct drm_encoder *encoder,
 		I915_WRITE(VIDEO_DIP_DATA, *data);
 		data++;
 	}
+	for (; i < 32; i += 4)
+		I915_WRITE(VIDEO_DIP_DATA, 0);
 	mmiowb();
 
 	val |= g4x_infoframe_enable(frame);
@@ -186,6 +188,8 @@ static void ibx_write_infoframe(struct drm_encoder *encoder,
 		I915_WRITE(TVIDEO_DIP_DATA(intel_crtc->pipe), *data);
 		data++;
 	}
+	for (; i < 32; i += 4)
+		I915_WRITE(TVIDEO_DIP_DATA(intel_crtc->pipe), 0);
 	mmiowb();
 
 	val |= g4x_infoframe_enable(frame);
@@ -224,6 +228,8 @@ static void cpt_write_infoframe(struct drm_encoder *encoder,
 		I915_WRITE(TVIDEO_DIP_DATA(intel_crtc->pipe), *data);
 		data++;
 	}
+	for (; i < 32; i += 4)
+		I915_WRITE(TVIDEO_DIP_DATA(intel_crtc->pipe), 0);
 	mmiowb();
 
 	val |= g4x_infoframe_enable(frame);
@@ -259,6 +265,8 @@ static void vlv_write_infoframe(struct drm_encoder *encoder,
 		I915_WRITE(VLV_TVIDEO_DIP_DATA(intel_crtc->pipe), *data);
 		data++;
 	}
+	for (; i < 32; i += 4)
+		I915_WRITE(VLV_TVIDEO_DIP_DATA(intel_crtc->pipe), 0);
 	mmiowb();
 
 	val |= g4x_infoframe_enable(frame);
@@ -292,6 +300,8 @@ static void hsw_write_infoframe(struct drm_encoder *encoder,
 		I915_WRITE(data_reg + i, *data);
 		data++;
 	}
+	for (; i < 32; i += 4)
+		I915_WRITE(data_reg + i, 0);
 	mmiowb();
 
 	val |= hsw_infoframe_enable(frame);
-- 
1.7.10.4