Checksumming was disabled for CEA blocks by
commit 4a638b4e38234233f5c7e6705662fbc0b58d80c2 Author: Adam Jackson ajax@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@rwth-aachen.de --- drivers/gpu/drm/drm_edid.c | 22 +++++++++++++++++++++- 1 file changed, 21 insertions(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c index 3a10f3f..55963d5 100644 --- a/drivers/gpu/drm/drm_edid.c +++ b/drivers/gpu/drm/drm_edid.c @@ -1203,6 +1203,7 @@ drm_do_get_edid(struct drm_connector *connector, struct i2c_adapter *adapter) { 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) @@ -1233,12 +1234,27 @@ drm_do_get_edid(struct drm_connector *connector, struct i2c_adapter *adapter)
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 (drm_do_probe_ddc_edid(adapter, ext_block, j, EDID_LENGTH)) goto out; - if (drm_edid_block_valid(ext_block, j, print_bad_edid)) { + csum = drm_edid_block_csum(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; } }
@@ -1249,6 +1265,9 @@ drm_do_get_edid(struct drm_connector *connector, struct i2c_adapter *adapter)
connector->bad_edid_counter++; } + + kfree(saved_block); + saved_block = NULL; }
if (valid_extensions != block[0x7e]) { @@ -1270,6 +1289,7 @@ carp: connector->bad_edid_counter++;
out: + kfree(saved_block); kfree(block); return NULL; }