[Intel-gfx] [PATCH] drm/i915/hdmi: Prune modes that require HDMI2.1 FRL

[Murthy, Arun R]

> -----Original Message-----
> From: Nautiyal, Ankit K <ankit.k.nautiyal at intel.com>
> Sent: Tuesday, July 19, 2022 11:40 AM
> To: Murthy, Arun R <arun.r.murthy at intel.com>; intel-
> gfx at lists.freedesktop.org
> Subject: Re: [Intel-gfx] [PATCH] drm/i915/hdmi: Prune modes that require
> HDMI2.1 FRL
> 
> 
> On 7/19/2022 8:45 AM, Murthy, Arun R wrote:
> >> -----Original Message-----
> >> From: Nautiyal, Ankit K <ankit.k.nautiyal at intel.com>
> >> Sent: Friday, July 8, 2022 3:36 PM
> >> To: Murthy, Arun R <arun.r.murthy at intel.com>; intel-
> >> gfx at lists.freedesktop.org
> >> Subject: Re: [Intel-gfx] [PATCH] drm/i915/hdmi: Prune modes that
> >> require
> >> HDMI2.1 FRL
> >>
> >> Hi Arun,
> >>
> >> Thanks for the comments.
> >>
> >> Please find my response inline.
> >>
> >> On 7/8/2022 9:30 AM, Murthy, Arun R wrote:
> >>>> -----Original Message-----
> >>>> From: Intel-gfx <intel-gfx-bounces at lists.freedesktop.org> On Behalf
> >>>> Of Ankit Nautiyal
> >>>> Sent: Thursday, July 7, 2022 10:57 AM
> >>>> To: intel-gfx at lists.freedesktop.org
> >>>> Subject: [Intel-gfx] [PATCH] drm/i915/hdmi: Prune modes that
> >>>> require
> >>>> HDMI2.1 FRL
> >>>>
> >>>> HDMI2.1 requires some higher resolution video modes to be
> >>>> enumerated only if HDMI2.1 Fixed Rate Link (FRL) is supported.
> >>>> Current platforms do not support FRL transmission so prune modes
> >>>> that require HDMI2.1 FRL.
> >>>>
> >>> If the hardware doesn't support FRL then it basically blocks HDMI2.1
> >> feature.
> >>> Then it wont be possible to use any resolution above 4k60 is it?
> >>
> >> Yes right. As I understand, the HDMI2.1a supersedes HDMI2.0b, and so
> >> the
> >>
> >> platforms  supporting HDMI2.0 must now pass the HDMI2.1 CTS.
> >> The HDMI2.1a spec introduces Marketing Feature names for 4K100,
> >> 4K120, 8k at 50, 8k at 60 with suffix A, and B.
> >> Suffix A meaning mode supported without compression, and B meaning,
> >> mode supported with compression.
> >>
> >> There are CTS tests that expect these modes not to be enumerated, if
> >> the source does support the given requirements.
> >>
> >>
> > Thanks for the clarification.
> >
> >>>> Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal at intel.com>
> >>>> ---
> >>>>    drivers/gpu/drm/i915/display/intel_hdmi.c | 21
> >> +++++++++++++++++++++
> >>>>    1 file changed, 21 insertions(+)
> >>>>
> >>>> diff --git a/drivers/gpu/drm/i915/display/intel_hdmi.c
> >>>> b/drivers/gpu/drm/i915/display/intel_hdmi.c
> >>>> index ebd91aa69dd2..93c00b61795f 100644
> >>>> --- a/drivers/gpu/drm/i915/display/intel_hdmi.c
> >>>> +++ b/drivers/gpu/drm/i915/display/intel_hdmi.c
> >>>> @@ -1974,6 +1974,20 @@ intel_hdmi_mode_clock_valid(struct
> >>>> drm_connector *connector, int clock,
> >>>>    	return status;
> >>>>    }
> >>>>
> >>>> +/*
> >>>> + * HDMI2.1 requires higher resolution modes like 8k60, 4K120 to be
> >>>> + * enumerated only if FRL is supported. Platforms not supporting
> >>>> +FRL
> >>>> + * must prune these modes.
> >>>> + */
> >>>> +static bool
> >>>> +hdmi21_frl_quirk(int dotclock, bool frl_supported) {
> >>>> +	if (dotclock >= 600000 && !frl_supported)
> >>>> +		return true;
> >>>> +
> >>>> +	return false;
> >>>> +}
> >>>> +
> >>>>    static enum drm_mode_status
> >>>>    intel_hdmi_mode_valid(struct drm_connector *connector,
> >>>>    		      struct drm_display_mode *mode) @@ -2001,6 +2015,13
> >> @@
> >>>> intel_hdmi_mode_valid(struct drm_connector *connector,
> >>>>    		clock *= 2;
> >>>>    	}
> >>>>
> >>>> +	/*
> >>>> +	 * Current Platforms do not support HDMI2.1 FRL mode of
> >>>> transmission,
> >>>> +	 * so prune the modes that require FRL.
> >>>> +	 */
> >>>> +	if (hdmi21_frl_quirk(clock, false))
> >>>> +		return MODE_BAD;
> >>>> +
> >>> Instead of setting this frl_supported as false, can we get this info
> >>> from hardware, so that when our hardware supports it later it would
> >>> be
> >> easy to enable this.
> >>
> >> We can have something like:
> >>
> >> src_supports_frl()
> >>
> >> {
> >>
> >> /* FRL not supported in
> >>
> >> return false;
> >>
> >> }
> >>
> > Yes something like this looks good. It would be a good design to judge
> > this based on the Display version.
> 
> I do agree, we need to have this check when we have HDMI2.1 support for
> any platform.
> 
> In future patches, when FRL transmission will be enabled, at that time it
> would make sense to check for display version, and parse from VBT about
> what rate it allows  etc.
> 
Awaiting patch with handling this properly!
Reviewed-by: Arun R Murthy <arun.r.murthy at intel.com>

Thanks and Regards,
Arun R Murthy
-------------------