[Intel-gfx] [PATCH 6/8] drm/edid: Add a FIXME about DispID CEA data block revision

[Shankar, Uma]

> -----Original Message-----
> From: Intel-gfx <intel-gfx-bounces at lists.freedesktop.org> On Behalf Of Ville Syrjala
> Sent: Saturday, January 25, 2020 1:32 AM
> To: dri-devel at lists.freedesktop.org
> Cc: intel-gfx at lists.freedesktop.org; Andres Rodriguez <andresx7 at gmail.com>
> Subject: [Intel-gfx] [PATCH 6/8] drm/edid: Add a FIXME about DispID CEA data block
> revision
> 
> From: Ville Syrjälä <ville.syrjala at linux.intel.com>
> 
> I don't understand what the DispID CEA data block revision means. The spec doesn't
> say. I guess some DispID must have a value of >= 3 in there or else we generally
> wouldn't even parse the CEA data blocks. Or does all this code actually not do
> anything?

This signifies the CTA extension revision (byte 1 of the block). As per the spec, seems like
Version 1 is legacy and 2 is deprecated. So version >=3 is checked here.
Refer section 7.3 of CTA-861-G

> Cc: Andres Rodriguez <andresx7 at gmail.com>
> Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
> ---
>  drivers/gpu/drm/drm_edid.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c index
> 0369a54e3d32..fd9b724067a7 100644
> --- a/drivers/gpu/drm/drm_edid.c
> +++ b/drivers/gpu/drm/drm_edid.c
> @@ -3977,6 +3977,13 @@ cea_db_tag(const u8 *db)  static int  cea_revision(const
> u8 *cea)  {
> +	/*
> +	 * FIXME is this correct for the DispID variant?
> +	 * The DispID spec doesn't really specify whether
> +	 * this is the revision of the CEA extension or
> +	 * the DispID CEA data block. And the only value
> +	 * given as an example is 0.
> +	 */
>  	return cea[1];
>  }
> 
> --
> 2.24.1
> 
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