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

[Ville Syrjälä]

On Tue, Mar 26, 2019 at 11:10:44AM -0700, Manasi Navare wrote:
> 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.

So r-b?

-- 
Ville Syrjälä
Intel