Checksumming was disabled for CEA blocks by
commit 4a638b4e38234233f5c7e6705662fbc0b58d80c2
Author: Adam Jackson <ajax at redhat.com>
Date: Tue May 25 16:33:09 2010 -0400
drm/edid: Allow non-fatal checksum errors in CEA blocks
If only the checksum is wrong, reading twice should result in identical
data, whereas a bad transfer will most likely corrupt different bytes.
Comparing checksums is not sufficient, as there is a considerable chance
of two bad transfers having the same checksum.
Signed-off-by: Stefan Brüns <stefan.bruens at rwth-aachen.de>
---
drivers/gpu/drm/drm_edid.c | 24 +++++++++++++++++++++++-
1 file changed, 23 insertions(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
index 31988ca..0b20fc9 100644
--- a/drivers/gpu/drm/drm_edid.c
+++ b/drivers/gpu/drm/drm_edid.c
@@ -1224,6 +1224,7 @@ struct edid *drm_do_get_edid(struct drm_connector
*connector,
{
int i, j = 0, valid_extensions = 0;
u8 *block, *new;
+ u8 *saved_block = NULL;
bool print_bad_edid = !connector->bad_edid_counter || (drm_debug &
DRM_UT_KMS);
if ((block = kmalloc(EDID_LENGTH, GFP_KERNEL)) == NULL)
@@ -1254,13 +1255,30 @@ struct edid *drm_do_get_edid(struct drm_connector
*connector,
for (j = 1; j <= block[0x7e]; j++) {
u8 *ext_block = block + (valid_extensions + 1) * EDID_LENGTH;
+ u8 csum, last_csum = 0;
for (i = 0; i < 4; i++) {
if (get_edid_block(data, ext_block, j, EDID_LENGTH))
goto out;
- if (drm_edid_block_valid(ext_block, j, print_bad_edid))
{
+ csum = drm_edid_block_checksum(ext_block);
+ if (!csum) {
valid_extensions++;
break;
+ } else if (ext_block[0] == CEA_EXT) {
+ /*
+ * Some switches mangle CEA contents without fixing the
checksum.
+ * Accept CEA blocks when two reads return identical
data.
+ */
+ if (saved_block && csum == last_csum &&
+ !memcmp(ext_block, saved_block,
EDID_LENGTH)) {
+ valid_extensions++;
+ break;
+ }
+ kfree(saved_block);
+ saved_block = kmemdup(ext_block, EDID_LENGTH,
GFP_KERNEL);
+ last_csum = csum;
}
+ if (print_bad_edid)
+ drm_dump_edid(ext_block);
}
if (i == 4 && print_bad_edid) {
@@ -1270,6 +1288,9 @@ struct edid *drm_do_get_edid(struct drm_connector
*connector,
connector->bad_edid_counter++;
}
+
+ kfree(saved_block);
+ saved_block = NULL;
}
if (valid_extensions != block[0x7e]) {
@@ -1291,6 +1312,7 @@ carp:
connector->bad_edid_counter++;
out:
+ kfree(saved_block);
kfree(block);
return NULL;
}
--
2.1.2
