Re: [PATCH 2/2] drm/i915/display: Force full modeset for eDP

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Fri, Feb 09, 2024 at 11:55:58AM +0000, Kahola, Mika wrote:
> > -----Original Message-----
> > From: Jani Nikula <jani.nikula@linux.intel.com>
> > Sent: Friday, February 9, 2024 11:06 AM
> > To: Kahola, Mika <mika.kahola@intel.com>; intel-gfx@lists.freedesktop.org
> > Cc: Kahola, Mika <mika.kahola@intel.com>
> > Subject: Re: [PATCH 2/2] drm/i915/display: Force full modeset for eDP
> > 
> > On Tue, 06 Feb 2024, Mika Kahola <mika.kahola@intel.com> wrote:
> > > Force full modeset for eDP when booting up. GOP programs PLL
> > > parameters and hence, we would be able to use fastset for eDP.
> > > However, with fastset we are not setting PLL values from the driver
> > > and rely that GOP and driver PLL values match.
> > > We have discovered that with some of the panels this is not true and
> > > hence we would need to program PLL values by the driver. The patch
> > > suggests a workaround as enabling full modeset when booting up. This
> > > way we force the driver to write the PLL values to the hw.
> > 
> > No. We want to avoid full modesets if possible, both in general and at probe.
> > 
> > And when we do end up with modesets, the decision needs to be based on changes in the state that we can't write to the
> > hardware without a modeset.
> > 
> > We can't unconditionally force a modeset on eDP panels at probe.
> 
> Thanks! Just wondering what the options here might be? With fastest we end up having a mismatch with one PLL value with a few panels.

You seem to be stuck in some infinite loop. If your PLL parameters
are mismatching that should prevent the fastset, but then I guess
you added some hack to allow the fastset despite the mismatch, and
now you're trying to undo that hack by blindly forcing a full
modeset?

> 
> Should we try identify the panels and setup some sort of quirks for these problematic panels or what would be the best solution?
> 
> -Mika-
> 
> > 
> > 
> > BR,
> > Jani.
> > 
> > >
> > > Signed-off-by: Mika Kahola <mika.kahola@intel.com>
> > > ---
> > >  drivers/gpu/drm/i915/display/intel_dp.c | 13 +++++++++++++
> > >  1 file changed, 13 insertions(+)
> > >
> > > diff --git a/drivers/gpu/drm/i915/display/intel_dp.c
> > > b/drivers/gpu/drm/i915/display/intel_dp.c
> > > index ab415f41924d..9699ded1eb5f 100644
> > > --- a/drivers/gpu/drm/i915/display/intel_dp.c
> > > +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> > > @@ -3319,6 +3319,7 @@ bool intel_dp_initial_fastset_check(struct intel_encoder *encoder,
> > >  	 * of crtc_state->dsc, we have no way to ensure reliable fastset.
> > >  	 * Remove once we have readout for DSC.
> > >  	 */
> > > +
> > >  	if (crtc_state->dsc.compression_enable) {
> > >  		drm_dbg_kms(&i915->drm, "[ENCODER:%d:%s] Forcing full modeset due to DSC being enabled\n",
> > >  			    encoder->base.base.id, encoder->base.name); @@ -3326,6
> > > +3327,18 @@ bool intel_dp_initial_fastset_check(struct intel_encoder *encoder,
> > >  		fastset = false;
> > >  	}
> > >
> > > +	/*
> > > +	 * FIXME hack to force full modeset for eDP as not always BIOS written PLL
> > > +	 * values does not match with the ones defined in the driver code
> > > +	 */
> > > +	if (!crtc_state->uapi.mode_changed &&
> > > +	    intel_dp_is_edp(intel_dp)) {
> > > +		drm_dbg_kms(&i915->drm, "Forcing full modeset for eDP\n");
> > > +		crtc_state->uapi.mode_changed = true;
> > > +		fastset = false;
> > > +	}
> > > +
> > > +
> > >  	return fastset;
> > >  }
> > 
> > --
> > Jani Nikula, Intel

-- 
Ville Syrjälä
Intel