[PATCH v2 05/18] DRM/KMS/EDID: Test EDDC if EDID announces more than one Extension Block (v2)

[Ville Syrjälä]

On Thu, Nov 22, 2012 at 05:22:55AM -0500, Egbert Eich wrote:
> There are displays which announce EDID extension blocks in the
> Extension Flag of the EDID base block although they are not EDDC
> capable (ie. take a segment address at I2C slave address 0x30).
> We test this by looking for an EDID header which is only possible
> in the base block.
> If the segment address is not taken into account, this block will
> be identical to the base block in which case we stop reading further
> EEDID blocks, correct the extension flag and just return the base
> block.
> 
> v2: Split up EDID fixup code into separate commit.
> 
> Signed-off-by: Egbert Eich <eich at suse.com>
> ---
>  drivers/gpu/drm/drm_edid.c |   13 +++++++++++++
>  1 files changed, 13 insertions(+), 0 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
> index a952cfe..5a0e331 100644
> --- a/drivers/gpu/drm/drm_edid.c
> +++ b/drivers/gpu/drm/drm_edid.c
> @@ -364,6 +364,19 @@ drm_do_get_edid(struct drm_connector *connector, struct i2c_adapter *adapter)
>  			}
>  			if (drm_edid_block_valid(block + (valid_extensions + 1) * EDID_LENGTH, j, print_bad_edid)) {
>  				valid_extensions++;
> +				/* Test if base block announced extension blocks although
> +				 * display is not EDDC capable.
> +				 */
> +				if (j == 2) {
> +					int k;
> +					for (k = 0; k < sizeof(edid_header); k++)
> +						if (block[(EDID_LENGTH * 2) + k] != edid_header[k])
> +							break;
> +					if (k == sizeof(edid_header)) {
> +						valid_extensions = 0;
> +						goto done_fix_extension_count;
> +					}

memcmp()? Also couldn't we just memcmp() the whole block against the base
block, instead of just the header part?

Also the comment is somehow misleading. It talks about the base block
even though we're looking at the extension block.

-- 
Ville Syrjälä
Intel OTC