Re: [PATCH 2/2] drm/i915/hdmi: Prune unsupported modes as per HDMI2.1 spec

["Nautiyal, Ankit K" <ankit.k.nautiyal@xxxxxxxxx>]

On 5/10/2022 12:31 PM, Ville Syrjälä wrote:
> On Mon, May 09, 2022 at 03:01:30PM +0530, Ankit Nautiyal wrote:
> > As per Sec 7.8.1 of HDMI2.1 spec, sources that support modes:
> > 4K100, 4K120, 8K50, 8K60 must support these modes in at least one of
> > the below formats:
> > i) uncompressed FRL, 420 format and min of 10 bpc, or
> > ii) compressed FRL, 444 format and min of 10 bpc.
> >
> > Since FRL and DSC are not supported natively with HDMI, the above
> > modes must be pruned as per the spec, and is a requirement for the
> > HDMI2.1 compliance test.
> >
> > This patch adds a condition to check for the modes with clock
> > requirement more than 2376 MHz (1188 MHz with 420 format),
> > and prune them if none of the above two formats are supported.
> Wy are we trying to pass HDMI-2.1 tests on a device that
> doesn't even support HDMI-2.1?

Hi Ville,

As I understand, the HDMI2.1a supersedes HDMI2.0b [1], and so these 
platforms must pass the HDMI2.1 CTS.
The HDMI2.1a spec introduces Marketing Feature names for 4K100, 4K120, 
8k@50, 8k@60 with suffix A, and B.
Suffix A meaning mode supported without compression, and B meaning, mode 
supported with compression.
e.g 4K@120AB marketing feature name means the device supports 4k@120 
both with and without compression.
But as per the spec, both variants of Marketing names require FRL to be 
supported along with other requirements.
There are tests that expect these modes not to be enumerated, if the 
source does support the given requirements.

[1] https://www.hdmi.org/spec/hdmi2_1

Regards,

Ankit

> > Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@xxxxxxxxx>
> > ---
> >   drivers/gpu/drm/i915/display/intel_hdmi.c | 48 +++++++++++++++++++++++
> >   1 file changed, 48 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/i915/display/intel_hdmi.c b/drivers/gpu/drm/i915/display/intel_hdmi.c
> > index 1ae09431f53a..2ee1262f6427 100644
> > --- a/drivers/gpu/drm/i915/display/intel_hdmi.c
> > +++ b/drivers/gpu/drm/i915/display/intel_hdmi.c
> > @@ -1940,6 +1940,44 @@ static bool intel_hdmi_sink_bpc_possible(struct drm_connector *connector,
> >   	}
> >   }
> >   
> > +/*
> > + * HDMI2.1 Sec7.8.1
> > + * Support requirement for 4K100, 4K120, 8K50, and 8K60.
> > + *
> > + * The modes with timings same as above modes are supported only with min of 10 bpc
> > + * along with:
> > + *
> > + * i) 444 format only with FRL mode support with DSC
> > + * ii) 420 format only with FRL mode without DSC.
> > + */
> > +static bool
> > +intel_hdmi21_bpc_possible(struct drm_connector *connector,
> > +			  int clock, int bpc, bool ycbcr420_output,
> > +			  bool frl, bool dsc)
> > +{
> > +	const struct drm_display_info *info = &connector->display_info;
> > +	const struct drm_hdmi_info *hdmi = &info->hdmi;
> > +
> > +	int pixel_clock = ycbcr420_output ? clock * 2 : clock;
> > +
> > +	if (pixel_clock < 2376000)
> > +		return true;
> > +
> > +	if (!frl)
> > +		return false;
> > +
> > +	if (dsc && bpc > hdmi->dsc_cap.bpc_supported)
> > +		return false;
> > +
> > +	if (!ycbcr420_output && !dsc)
> > +		return false;
> > +
> > +	if (bpc < 10)
> > +		return false;
> > +
> > +	return true;
> > +}
> > +
> >   static enum drm_mode_status
> >   intel_hdmi_mode_clock_valid(struct drm_connector *connector, int clock,
> >   			    bool has_hdmi_sink, bool ycbcr420_output)
> > @@ -1948,6 +1986,13 @@ intel_hdmi_mode_clock_valid(struct drm_connector *connector, int clock,
> >   	struct intel_hdmi *hdmi = intel_attached_hdmi(to_intel_connector(connector));
> >   	enum drm_mode_status status = MODE_OK;
> >   	int bpc;
> > +	bool frl, dsc;
> > +
> > +	/*
> > +	 * FRL and DSC not supported for HDMI from source as of now.
> > +	 */
> > +	frl = false;
> > +	dsc = false;
> >   
> >   	/*
> >   	 * Try all color depths since valid port clock range
> > @@ -1963,6 +2008,9 @@ intel_hdmi_mode_clock_valid(struct drm_connector *connector, int clock,
> >   		if (!intel_hdmi_sink_bpc_possible(connector, bpc, has_hdmi_sink, ycbcr420_output))
> >   			continue;
> >   
> > +		if (!intel_hdmi21_bpc_possible(connector, clock, bpc, ycbcr420_output, frl, dsc))
> > +			continue;
> > +
> >   		status = hdmi_port_clock_valid(hdmi, tmds_clock, true, has_hdmi_sink);
> >   		if (status == MODE_OK)
> >   			return MODE_OK;
> > --
> > 2.25.1