[PATCH] drm/edid: Refine HDMI VSDB detect

[Ville Syrjälä]

On Sun, Dec 12, 2021 at 11:33:31PM +0800, Lee Shawn C wrote:
> According to CEA-861-F chapter 7.5.4. It says "The VSDB shall contain the
> 3 bytes of the IEEE OUI as well as any additional payload bytes needed."
> Now DRM driver check HDMI OUI but VSDB payload size at least five bytes.
> That may caused some HDMI monitors' audio feature can't be enabled.
> Because of they only have three bytes payload (OUI only) in VSDB.

HDMI 1.4a says
"Sinks shall contain an HDMI VSDB minimally containing a 2-byte Source
 Physical Address field following the 24-bit identifier. ...
 The minimum value of N (length) is 5 and the maximum value of N is 31."

Do you actually have an EDID that violates that?

> 
> Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
> Cc: Adam Jackson <ajax at redhat.com>
> Cc: Dave Airlie <airlied at redhat.com>
> Signed-off-by: Lee Shawn C <shawn.c.lee at intel.com>
> ---
>  drivers/gpu/drm/drm_edid.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
> index 12893e7be89b..5aa4a6bf4a13 100644
> --- a/drivers/gpu/drm/drm_edid.c
> +++ b/drivers/gpu/drm/drm_edid.c
> @@ -4205,7 +4205,7 @@ static bool cea_db_is_hdmi_vsdb(const u8 *db)
>  	if (cea_db_tag(db) != VENDOR_BLOCK)
>  		return false;
>  
> -	if (cea_db_payload_len(db) < 5)
> +	if (cea_db_payload_len(db) < 3)
>  		return false;
>  
>  	return oui(db[3], db[2], db[1]) == HDMI_IEEE_OUI;
> -- 
> 2.31.1

-- 
Ville Syrjälä
Intel