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, Jani Nikula <jani.nikula@linux.intel.com> wrote:
> 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.

I think we should also have a bug filed on this, with the offending EDID
attached for posterity.

BR,
Jani.


>>
>> 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