On Sun, 16 Nov 2014, Stefan Brüns <stefan.bruens@xxxxxxxxxxxxxx> 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@xxxxxxxxxx>
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@xxxxxxxxxxxxxx>
> ---
> 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;
> 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)) {
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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--
Jani Nikula, Intel Open Source Technology Center
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