From 4207f2e2926e416bc35787ced444a39fe0d29b97 Mon Sep 17 00:00:00 2001
From: Jani Nikula <jani.nikula@intel.com>
Date: Wed, 8 Jun 2022 10:50:31 +0300
Subject: drm/edid: fix CTA data block collection size for CTA version 3
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Git-commit: fc67615f4ecc3b66bd458840927272aa131eface
Patch-mainline: v6.0-rc1
References: jsc#PED-1166 jsc#PED-1168 jsc#PED-1170 jsc#PED-1218 jsc#PED-1220 jsc#PED-1222 jsc#PED-1223 jsc#PED-1225 jsc#PED-2849

The CTA Data Block Collection is valid only for CTA extension version
3. In versions 1 and 2, it is a reserved block, which we ignore.

The DTD start offset (byte 2, or d in CTA-861 spec), which determines
the CTA Data Block Collection size, is specified slightly differently
for different versions:

Version 1:
    d = offset for the byte following the reserved data block. If no
    data is provided in the reserved data block, then d=4. If no DTDs
    are provided, then d=0

Version 2:
    d = offset for the byte following the reserved data block. If no
    data is provided in the reserved data block, then d=4. If d=0, then
    no detailed timing descriptors are provided, and no data is provided
    in the reserved data block.

Version 3:
    d = offset for the byte following the data block collection. If no
    data is provided in the data block collection, then d=4. If d=0,
    then no detailed timing descriptors are provided, and no data is
    provided in the data block collection.

Ever since commit 9e50b9d55e9c ("drm: edid: Add some bounds checking"),
we've interpreted 0 to mean there are no DTDs but it's all Data
Blocks. Per the spec, Data Blocks are only valid for version 3, where we
should interpret 0 to mean there are no data blocks.

Follow the spec (and hope the EDIDs follow it too).

Cc: Ville Syrj채l채 <ville.syrjala@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Ville Syrj채l채 <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/2a4c94417f024cbafc5d4ca0a74e4617fc4325d1.1654674560.git.jani.nikula@intel.com
Acked-by: Patrik Jakobsson <pjakobsson@suse.de>
---
 drivers/gpu/drm/drm_edid.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
index 929fc0e46751..c57f6333ea7d 100644
--- a/drivers/gpu/drm/drm_edid.c
+++ b/drivers/gpu/drm/drm_edid.c
@@ -4498,8 +4498,6 @@ static const void *__cea_db_iter_edid_next(struct cea_db_iter *iter)
 
 		iter->index = 4;
 		iter->end = ext[2];
-		if (iter->end == 0)
-			iter->end = 127;
 		if (iter->end < 4 || iter->end > 127)
 			continue;
 
-- 
2.38.1