On Sun, 16 Nov 2014, Stefan Brüns stefan.bruens@rwth-aachen.de wrote:
4a638b4e38234233f5c7e6705662fbc0b58d80c2 disabled the checksumming
Please include the subject of the referenced commit, e.g.
4a638b4e3823 drm/edid: Allow non-fatal checksum errors in CEA blocks
or
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
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;
This bit could be a non-functional prep patch.
u8 csum, last_csum = 0;
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)) {
Now you skip drm_edid_block_valid for all blocks?
if ((csum = drm_edid_block_checksum(ext_block)) == 0) {
Please don't assign within the if condition.
valid_extensions++; break;
} else if ((ext_block[0] == CEA_EXT) && (csum == last_csum)) {
Too many braces.
Perhaps it would be sufficient to just check checksums instead of comparing the data? *shrug*.
/** Some switches mangle CEA contents without fixing the checksum.* Accept CEA blocks when two reads return identical data.*/
So you end up here on the 2nd time you get identical checksums, but you don't have the saved_block for the 1st attempt. Therefore you end up saving the 2nd attempt and go for a 3rd attempt to end up here.
if (!saved_block)saved_block = kmalloc(EDID_LENGTH, GFP_KERNEL);if (saved_block && !memcmp(ext_block, saved_block, EDID_LENGTH)) {
On the 2nd attempt you compare ext_block to whatever kmalloc returned you.
valid_extensions++;break;}if (saved_block)memcpy(saved_block, ext_block, EDID_LENGTH);
You should use kmemdup, and rearrange the code to do what it says on the commit message.
BR, Jani.
}
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;
}
1.8.4.5
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