[Intel-gfx] [PATCH 1/2] drm/i915: Do not enable FEC without DSC

[Manasi Navare]

On Tue, Mar 26, 2019 at 06:16:57PM +0200, Ville Syrjälä wrote:
> On Tue, Mar 26, 2019 at 09:00:27AM -0700, Manasi Navare wrote:
> > On Tue, Mar 26, 2019 at 04:49:02PM +0200, Ville Syrjala wrote:
> > > From: Ville Syrjälä <ville.syrjala at linux.intel.com>
> > > 
> > > Currently we enable FEC even when DSC is no used. While that is
> > > theoretically valid supposedly there isn't much of a benefit from
> > > this. But more importantly we do not account for the FEC link
> > > bandwidth overhead (2.4%) in the non-DSC link bandwidth computations.
> > > So the code may think we have enough bandwidth when we in fact
> > > do not.
> > > 
> > > Cc: Anusha Srivatsa <anusha.srivatsa at intel.com>
> > > Cc: Manasi Navare <manasi.d.navare at intel.comk>
> > > Fixes: 240999cf339f ("i915/dp/fec: Add fec_enable to the crtc state.")
> > > Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
> > > ---
> > >  drivers/gpu/drm/i915/intel_dp.c | 6 +++---
> > >  1 file changed, 3 insertions(+), 3 deletions(-)
> > > 
> > > diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> > > index 326de12c3f44..bbf678561509 100644
> > > --- a/drivers/gpu/drm/i915/intel_dp.c
> > > +++ b/drivers/gpu/drm/i915/intel_dp.c
> > > @@ -1925,6 +1925,9 @@ static int intel_dp_dsc_compute_config(struct intel_dp *intel_dp,
> > >  	int pipe_bpp;
> > >  	int ret;
> > >  
> > > +	pipe_config->fec_enable = !intel_dp_is_edp(intel_dp) &&
> > > +		intel_dp_supports_fec(intel_dp, pipe_config);
> > > +
> > 
> > We could still not enable DSC after this point since it has more checks in this
> > function. Even though in that case we would fail the encoder config so wouldnt
> > matter if we have enabled FEC or not, but its less intutive.
> > IMHO, the ideal place to set the fec enable is in intel_dp_compute_link_config()
> > after the all to dsc_compute_config and set it only if pipe_config->dsc_params.compression_enable
> 
> That would require changing intel_dp_supports_dsc() which I decided
> wasn't worth the hassle.

Hmm, yea because intel_dp_supports_dsc depends on fec_enable.
In that case we would need to change that to use intel_dp_supports_fec(). TBH that makes more sense since
we should set dp_supports based on HW FEC capability and then set the crtc_state->fec_enable based
on crtc_state->dsc_params.compression_enable. But since it doesnt change the functionality, I am ok
either ways.

Manasi

> 
> > 
> > Manasi
> > 
> > >  	if (!intel_dp_supports_dsc(intel_dp, pipe_config))
> > >  		return -EINVAL;
> > >  
> > > @@ -2168,9 +2171,6 @@ intel_dp_compute_config(struct intel_encoder *encoder,
> > >  	if (adjusted_mode->flags & DRM_MODE_FLAG_DBLCLK)
> > >  		return -EINVAL;
> > >  
> > > -	pipe_config->fec_enable = !intel_dp_is_edp(intel_dp) &&
> > > -				  intel_dp_supports_fec(intel_dp, pipe_config);
> > > -
> > >  	ret = intel_dp_compute_link_config(encoder, pipe_config, conn_state);
> > >  	if (ret < 0)
> > >  		return ret;
> > > -- 
> > > 2.19.2
> > > 
> > > _______________________________________________
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> > > Intel-gfx at lists.freedesktop.org
> > > https://lists.freedesktop.org/mailman/listinfo/intel-gfx
> 
> -- 
> Ville Syrjälä
> Intel