Re: [PATCH] drm/edid: ignore the CEA modes not defined in CEA-861-D

[Jani Nikula <jani.nikula@linux.intel.com>]

On Tue, 31 May 2022, William Tseng <william.tseng@intel.com> wrote:
> This is a workaround for HDMI 1.4 sink which has a CEA mode with higher vic
> than what is defined in CEA-861-D.
>
> As an example, a HDMI 1.4 sink has the video format 2560x1080p to be
> displayed and the video format is indicated by both SVD (with vic 90 and
> pictuure aspect ratio 64:27) and DTD.  When connecting to such sink,
> source can't output the video format in SVD because an error is returned by
> drm_hdmi_avi_infoframe_from_display_mode(), which can't fill the infoframe
> with pictuure aspect ratio 64:27 and the vic, which is originally 90 and is
> changed to 0 by drm_mode_cea_vic().
>
> To work around it, this patch ignores such CEA modes in do_cea_modes() so
> the modes won't be processed in drm_hdmi_avi_infoframe_from_display_mode().
> And only the video format in DTD can be dispalyed.
>
> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> Cc: Wayne Lin <waynelin@amd.com>
> Cc: Lee Shawn C <shawn.c.lee@intel.com>
> Signed-off-by: William Tseng <william.tseng@intel.com>
> ---
>  drivers/gpu/drm/drm_edid.c | 39 +++++++++++++++++++++++++-------------
>  1 file changed, 26 insertions(+), 13 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
> index bc43e1b32092..a93f68878bfd 100644
> --- a/drivers/gpu/drm/drm_edid.c
> +++ b/drivers/gpu/drm/drm_edid.c
> @@ -3982,6 +3982,19 @@ drm_display_mode_from_cea_vic(struct drm_device *dev,
>  }
>  EXPORT_SYMBOL(drm_display_mode_from_cea_vic);
>  
> +static bool is_hdmi2_sink(const struct drm_connector *connector)
> +{
> +	/*
> +	 * FIXME: sil-sii8620 doesn't have a connector around when
> +	 * we need one, so we have to be prepared for a NULL connector.
> +	 */
> +	if (!connector)
> +		return true;
> +
> +	return connector->display_info.hdmi.scdc.supported ||
> +		connector->display_info.color_formats & DRM_COLOR_FORMAT_YCBCR420;
> +}
> +
>  static int
>  do_cea_modes(struct drm_connector *connector, const u8 *db, u8 len)
>  {
> @@ -3993,6 +4006,19 @@ do_cea_modes(struct drm_connector *connector, const u8 *db, u8 len)
>  
>  		mode = drm_display_mode_from_vic_index(connector, db, len, i);
>  		if (mode) {
> +			u8 vic = svd_to_vic(db[i]);
> +
> +			if (!drm_valid_cea_vic(vic))
> +				continue;

drm_display_mode_from_vic_index() returns NULL in this case.

> +
> +			/*
> +			 * HDMI 1.4 VIC range: 1 <= VIC <= 64 (CEA-861-D) but
> +			 * HDMI 2.0 VIC range: 1 <= VIC <= 107 (CEA-861-F). So we
> +			 * have to make sure we dont break HDMI 1.4 sinks.
> +			 */
> +			if (!is_hdmi2_sink(connector) && vic > 64)
> +				continue;

I'll need to double check if this is the right thing to do... but I
guess the question becomes if this shouldn't be within
drm_display_mode_from_vic_index().

Duplicating the condition from drm_mode_cea_vic() is probably not a good
idea.

The continues in both above branches leak the mode.


BR,
Jani.


> +
>  			/*
>  			 * YCBCR420 capability block contains a bitmap which
>  			 * gives the index of CEA modes from CEA VDB, which
> @@ -5846,19 +5872,6 @@ void drm_set_preferred_mode(struct drm_connector *connector,
>  }
>  EXPORT_SYMBOL(drm_set_preferred_mode);
>  
> -static bool is_hdmi2_sink(const struct drm_connector *connector)
> -{
> -	/*
> -	 * FIXME: sil-sii8620 doesn't have a connector around when
> -	 * we need one, so we have to be prepared for a NULL connector.
> -	 */
> -	if (!connector)
> -		return true;
> -
> -	return connector->display_info.hdmi.scdc.supported ||
> -		connector->display_info.color_formats & DRM_COLOR_FORMAT_YCBCR420;
> -}
> -
>  static u8 drm_mode_hdmi_vic(const struct drm_connector *connector,
>  			    const struct drm_display_mode *mode)
>  {

-- 
Jani Nikula, Intel Open Source Graphics Center