[PATCH 04/17] DRM/KMS/EDID: Test EDDC if EDID announces more than one Extension Block.

[Egbert Eich]

There are displays which announce EDID extension blocks in the
Extension Flag of the EDID base block although they are not EDDC
capable (ie. take a segment address at I2C slave address 0x30).
We test this by looking for an EDID header which is only possible
in the base block.
If the segment address is not taken into account, this block will
be identical to the base block in which case we stop reading further
EEDID blocks, correct the extension flag and just return the base
block.

Signed-off-by: Egbert Eich <eich at suse.de>
---
 drivers/gpu/drm/drm_edid.c |   13 +++++++++++++
 1 files changed, 13 insertions(+), 0 deletions(-)

diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
index b258646..ec6f3bb 100644
--- a/drivers/gpu/drm/drm_edid.c
+++ b/drivers/gpu/drm/drm_edid.c
@@ -361,6 +361,19 @@ drm_do_get_edid(struct drm_connector *connector, struct i2c_adapter *adapter)
 			}
 			if (drm_edid_block_valid(block + (valid_extensions + 1) * EDID_LENGTH, j, print_bad_edid)) {
 				valid_extensions++;
+				/* Test if base block announced extension blocks although
+				 * display is not EDDC capable.
+				 */
+				if (j == 2) {
+					int k;
+					for (k = 0; k < sizeof(edid_header); k++)
+						if (block[(EDID_LENGTH * 2) + k] != edid_header[k])
+							break;
+					if (k == sizeof(edid_header)) {
+						valid_extensions = 0;
+						goto no_more;
+					}
+				}
 				break;
 			}
 		}
-- 
1.7.7