[v3] drm/edid: check basic audio support on CEA extension block

[Lee Shawn C]

From: Cooper Chiou <cooper.chiou at intel.com>

Tag code stored in bit7:5 for CTA block byte[3] is not the same as
CEA extension block definition. Only check CEA block has
basic audio support.

v3: update commit message.

Cc: stable at vger.kernel.org
Cc: Jani Nikula <jani.nikula at intel.com>
Cc: Shawn C Lee <shawn.c.lee at intel.com>
Cc: intel-gfx <intel-gfx at lists.freedesktop.org>
Signed-off-by: Cooper Chiou <cooper.chiou at intel.com>
Signed-off-by: Lee Shawn C <shawn.c.lee at intel.com>
Fixes: e28ad544f462 ("drm/edid: parse CEA blocks embedded in DisplayID")
Reviewed-by: Jani Nikula <jani.nikula at intel.com>
---
 drivers/gpu/drm/drm_edid.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
index 561f53831e29..f07af6786cec 100644
--- a/drivers/gpu/drm/drm_edid.c
+++ b/drivers/gpu/drm/drm_edid.c
@@ -4859,7 +4859,8 @@ bool drm_detect_monitor_audio(struct edid *edid)
 	if (!edid_ext)
 		goto end;
 
-	has_audio = ((edid_ext[3] & EDID_BASIC_AUDIO) != 0);
+	has_audio = (edid_ext[0] == CEA_EXT &&
+		    (edid_ext[3] & EDID_BASIC_AUDIO) != 0);
 
 	if (has_audio) {
 		DRM_DEBUG_KMS("Monitor has basic audio support\n");
-- 
2.17.1