4a638b4e38234233f5c7e6705662fbc0b58d80c2 disabled the checksumming for CEA blocks. If only the checksum is wrong, reading twice should result in identical data, whereas a bad transfer will most likely corrupt diffent bytes.
Signed-off-by: Stefan Brüns stefan.bruens@rwth-aachen.de --- drivers/gpu/drm/drm_edid.c | 25 +++++++++++++++++++++---- 1 file changed, 21 insertions(+), 4 deletions(-)
diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c index 505960e..9b6b65e 100644 --- a/drivers/gpu/drm/drm_edid.c +++ b/drivers/gpu/drm/drm_edid.c @@ -1200,6 +1200,7 @@ 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) @@ -1234,15 +1235,29 @@ drm_do_get_edid(struct drm_connector *connector, struct i2c_adapter *adapter) block = new;
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, - block + (valid_extensions + 1) * EDID_LENGTH, - j, EDID_LENGTH)) + if (drm_do_probe_ddc_edid(adapter, ext_block, j, EDID_LENGTH)) goto out; - if (drm_edid_block_valid(block + (valid_extensions + 1) * EDID_LENGTH, j, print_bad_edid)) { + if ((csum = drm_edid_block_checksum(ext_block)) == 0) { valid_extensions++; break; + } else if ((ext_block[0] == CEA_EXT) && (csum == last_csum)) { + /* + * Some switches mangle CEA contents without fixing the checksum. + * Accept CEA blocks when two reads return identical data. + */ + if (!saved_block) + saved_block = kmalloc(EDID_LENGTH, GFP_KERNEL); + if (saved_block && !memcmp(ext_block, saved_block, EDID_LENGTH)) { + valid_extensions++; + break; + } + if (saved_block) + memcpy(saved_block, ext_block, EDID_LENGTH); } + last_csum = csum; }
if (i == 4 && print_bad_edid) { @@ -1263,6 +1278,7 @@ drm_do_get_edid(struct drm_connector *connector, struct i2c_adapter *adapter) block = new; }
+ kfree(saved_block); return block;
carp: @@ -1273,6 +1289,7 @@ carp: connector->bad_edid_counter++;
out: + kfree(saved_block); kfree(block); return NULL; }