From: Fangzhi Zuo <Jerry.Zuo@amd.com>

[ Upstream commit 9b3aa1dec7c364b0d7b171dcc00ab1092e362aef ]

[why]
The 8K120/8K240 timings live in DisplayID extension blocks 2 and 3
of this EDID. The EDID is a 4-block (512-byte) HDMI 2.1 EDID
that uses HF-EEODB.
drm core reads and parses this correctly, but amdgpu rebuilds its own copy.
Only 2 of 4 blocks were copied into sink->dc_edid, that leads to
drm_edid_connector_add_modes() never sees blocks 2 and 3.

[how]
Directly populate edid_blob_ptr with a blob whose length is the full,
and HF-EEODB-aware size.

Reviewed-by: Sun peng (Leo) Li <sunpeng.li@amd.com>
Signed-off-by: Fangzhi Zuo <Jerry.Zuo@amd.com>
Signed-off-by: George Zhang <george.zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit 11a90eaf5c808ba800249dda0d481c35d0888589)
Signed-off-by: Sasha Levin <sashal@kernel.org>
---

LLM Generated explanations, may be completely bogus:

The branch check finished: commit `11a90eaf5c808` (“Fix 8K Mode Not
Parsed by EDID”) is on `linux-next/master` only, not in the local
`v6.18.44` tree. That matches the earlier finding — the fix is in
mainline development and still needs to be backported to 6.18.y if
selected.

The backport recommendation remains **YES** for this tree.

 .../amd/display/amdgpu_dm/amdgpu_dm_helpers.c | 20 ++++++++++++++++---
 1 file changed, 17 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_helpers.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_helpers.c
index d0f770dd0a956..c2de763d621d3 100644
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_helpers.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_helpers.c
@@ -1031,11 +1031,25 @@ enum dc_edid_status dm_helpers_read_local_edid(
 			continue;
 
 		edid = drm_edid_raw(drm_edid); // FIXME: Get rid of drm_edid_raw()
-		if (!edid ||
-		    edid->extensions >= sizeof(sink->dc_edid.raw_edid) / EDID_LENGTH)
+		/*
+		 * Use the length of the EDID property blob populated by
+		 * drm_edid_connector_update() above. It reflects the true number
+		 * of EDID blocks, including any HDMI Forum EDID Extension Override
+		 * Data Block (HF-EEODB) count, which the raw byte 0x7e extension
+		 * count can hide (e.g. HDMI 8K sinks).
+		 */
+		if (!edid || !connector->edid_blob_ptr ||
+		    connector->edid_blob_ptr->length > sizeof(sink->dc_edid.raw_edid))
 			return EDID_BAD_INPUT;
 
-		sink->dc_edid.length = EDID_LENGTH * (edid->extensions + 1);
+		/*
+		 * FIXME: amdgpu_dm today does not consider the HF-EEODB, which
+		 * may contain additional mode info for sinks. This is a
+		 * workaround until dc_edid is refactored out from DC into
+		 * amdgpu_dm's ownership, allowing amdgpu_dm to use drm_edid
+		 * directly
+		 */
+		sink->dc_edid.length = connector->edid_blob_ptr->length;
 		memmove(sink->dc_edid.raw_edid, (uint8_t *)edid, sink->dc_edid.length);
 
 		/* We don't need the original edid anymore */
-- 
2.53.0