linux-kernel - [ 061/147] drm/i915: make sure we write all the DIP data bytes

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Message-Id: <20121014143542.113662367@decadent.org.uk>
Date:	Sun, 14 Oct 2012 15:36:34 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	Paulo Zanoni <paulo.r.zanoni@...el.com>,
	Rodrigo Vivi <rodrigo.vivi@...il.com>,
	Daniel Vetter <daniel.vetter@...ll.ch>
Subject: [ 061/147] drm/i915: make sure we write all the DIP data bytes

3.2-stable review patch.  If anyone has any objections, please let me know.

------------------

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

commit adf00b26d18e1b3570451296e03bcb20e4798cdd upstream.

... even if the actual infoframe is smaller than the maximum possible
size.

If we don't write all the 32 DIP data 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.

Notice that on IVB and older we actually have 64 bytes available for
VIDEO_DIP_DATA, but only bytes 0-31 actually store infoframe data: the
others are either read-only ECC values or marked as "reserved". On HSW
we only have 32 bytes, and the ECC value is stored on its own separate
read-only register. See BSpec.

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.

Version 2:
  - Improve commit message
  - Try to make the code more clear

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=46761
Signed-off-by: Paulo Zanoni <paulo.r.zanoni@...el.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@...il.com>
Signed-off-by: Daniel Vetter <daniel.vetter@...ll.ch>
[bwh: Backported to 3.2: only two write_infoframe functions to be modified]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/gpu/drm/i915/i915_reg.h   |    4 ++++
 drivers/gpu/drm/i915/intel_hdmi.c |   15 +++++++++++++++
 2 files changed, 19 insertions(+)

--- a/drivers/gpu/drm/i915/i915_reg.h
+++ b/drivers/gpu/drm/i915/i915_reg.h
@@ -1557,6 +1557,10 @@
 
 /* Video Data Island Packet control */
 #define VIDEO_DIP_DATA		0x61178
+/* Read the description of VIDEO_DIP_DATA (before Haswel) or VIDEO_DIP_ECC
+ * (Haswell and newer) to see which VIDEO_DIP_DATA byte corresponds to each byte
+ * of the infoframe structure specified by CEA-861. */
+#define   VIDEO_DIP_DATA_SIZE	32
 #define VIDEO_DIP_CTL		0x61170
 #define   VIDEO_DIP_ENABLE		(1 << 31)
 #define   VIDEO_DIP_PORT_B		(1 << 29)
--- a/drivers/gpu/drm/i915/intel_hdmi.c
+++ b/drivers/gpu/drm/i915/intel_hdmi.c
@@ -143,6 +143,9 @@ static void i9xx_write_infoframe(struct
 		I915_WRITE(VIDEO_DIP_DATA, *data);
 		data++;
 	}
+	/* Write every possible data byte to force correct ECC calculation. */
+	for (; i < VIDEO_DIP_DATA_SIZE; i += 4)
+		I915_WRITE(VIDEO_DIP_DATA, 0);
 	mmiowb();
 
 	flags |= intel_infoframe_flags(frame);
@@ -176,6 +179,9 @@ static void ironlake_write_infoframe(str
 		I915_WRITE(TVIDEO_DIP_DATA(intel_crtc->pipe), *data);
 		data++;
 	}
+	/* Write every possible data byte to force correct ECC calculation. */
+	for (; i < VIDEO_DIP_DATA_SIZE; i += 4)
+		I915_WRITE(TVIDEO_DIP_DATA(intel_crtc->pipe), 0);
 	mmiowb();
 
 	flags |= intel_infoframe_flags(frame);


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