[Intel-gfx] [PATCH] drm/i915/dsc: Remove redundant checks in DSC disable

[Kulkarni, Vandita]

> -----Original Message-----
> From: Manna, Animesh <animesh.manna at intel.com>
> Sent: Thursday, June 3, 2021 7:24 PM
> To: Kulkarni, Vandita <vandita.kulkarni at intel.com>; Nikula, Jani
> <jani.nikula at intel.com>; Saarinen, Jani <jani.saarinen at intel.com>; intel-
> gfx at lists.freedesktop.org
> Cc: Navare, Manasi D <manasi.d.navare at intel.com>
> Subject: RE: [Intel-gfx] [PATCH] drm/i915/dsc: Remove redundant checks in
> DSC disable
> 
> 
> 
> > -----Original Message-----
> > From: Kulkarni, Vandita <vandita.kulkarni at intel.com>
> > Sent: Thursday, June 3, 2021 4:55 PM
> > To: Nikula, Jani <jani.nikula at intel.com>; Saarinen, Jani
> > <jani.saarinen at intel.com>; intel-gfx at lists.freedesktop.org
> > Cc: Manna, Animesh <animesh.manna at intel.com>; Navare, Manasi D
> > <manasi.d.navare at intel.com>
> > Subject: RE: [Intel-gfx] [PATCH] drm/i915/dsc: Remove redundant checks
> > in DSC disable
> >
> > > -----Original Message-----
> > > From: Nikula, Jani <jani.nikula at intel.com>
> > > Sent: Thursday, June 3, 2021 3:11 PM
> > > To: Kulkarni, Vandita <vandita.kulkarni at intel.com>; Saarinen, Jani
> > > <jani.saarinen at intel.com>; intel-gfx at lists.freedesktop.org
> > > Cc: Manna, Animesh <animesh.manna at intel.com>; Navare, Manasi D
> > > <manasi.d.navare at intel.com>
> > > Subject: RE: [Intel-gfx] [PATCH] drm/i915/dsc: Remove redundant
> > > checks in DSC disable
> > >
> > > On Thu, 03 Jun 2021, "Kulkarni, Vandita"
> > > <vandita.kulkarni at intel.com>
> > > wrote:
> > > >> -----Original Message-----
> > > >> From: Saarinen, Jani <jani.saarinen at intel.com>
> > > >> Sent: Thursday, June 3, 2021 1:07 PM
> > > >> To: Kulkarni, Vandita <vandita.kulkarni at intel.com>; intel-
> > > >> gfx at lists.freedesktop.org
> > > >> Cc: Nikula, Jani <jani.nikula at intel.com>
> > > >> Subject: RE: [Intel-gfx] [PATCH] drm/i915/dsc: Remove redundant
> > > >> checks in DSC disable
> > > >>
> > > >> Hi,
> > > >> > -----Original Message-----
> > > >> > From: Intel-gfx <intel-gfx-bounces at lists.freedesktop.org> On
> > > >> > Behalf Of Vandita Kulkarni
> > > >> > Sent: torstai 3. kesäkuuta 2021 9.54
> > > >> > To: intel-gfx at lists.freedesktop.org
> > > >> > Cc: Nikula, Jani <jani.nikula at intel.com>
> > > >> > Subject: [Intel-gfx] [PATCH] drm/i915/dsc: Remove redundant
> > > >> > checks in DSC disable
> > > >> >
> > > >> > There can be a chance that pre os has enabled DSC and driver's
> > > >> > compute config would not need dsc to be enabled, in such case
> > > >> > if we check on compute config's compression state to disable,
> > > >> > we might end up in state
> > > >> mismatch.
> > > >>
> > > >> I assume this fixes real gitlab issue too?
> > > > Okay, will add the tag
> > > > Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/3537
> > >
> > > See https://lore.kernel.org/r/87fsxzp9qx.fsf@intel.com
> > >
> > > The problem is with ->bigjoiner, not the entire statement.
> > Thanks for pointing this out, true that bigjoiner not being enabled
> > will stop dsc disabling.
> > The bigjoiner check was making the entire condition check unnecessary.
> >
> > Will update and refloat.
> 
> Hi Jani/Vandita,
> 
> For uncompressed bigjoiner case if we want to use the same function to
> clear the dsc_ctrl1 register we may need to remove both the condition
> check.
> As for uncompressed bigjoiner case, compression_enable Will be 0 and will
> block in clearing the dss_ctl1_reg.

Yes, I was going through and found that bit 20 and 21 of dss_ctl1 are being used
for uncompressed joiner.
So when dsc is not enabled to avoid writing the register we could add
below code .

if (dsc)
	clear dss_ctl2
if ( bigjoiner | dsc)
	clear dss_ctl1;
return;

bigjoiner = 1 and dsc = 0  - uncompressed , I think there is no harm in clearing dsc bits again
bigjoiner = 1 and dsc = 1 - compressed - uncompressed bits are already 0
bigjoiner = 0 and dsc= 1 - just dsc  - clear dsc rest are 0s already
bigjoiner = 0 and dsc = 0  do nothing, return

If I have missed any corner case, please let me know.

Thanks,
Vandita
> 
> Regards,
> Animesh
> >
> > Thanks,
> > Vandita
> > >
> > >
> > > BR,
> > > Jani.
> > >
> > > >
> > > > Thanks,
> > > > Vandita
> > > >>
> > > >> >
> > > >> > Signed-off-by: Vandita Kulkarni <vandita.kulkarni at intel.com>
> > > >> > ---
> > > >> >  drivers/gpu/drm/i915/display/intel_vdsc.c | 4 ----
> > > >> >  1 file changed, 4 deletions(-)
> > > >> >
> > > >> > diff --git a/drivers/gpu/drm/i915/display/intel_vdsc.c
> > > >> > b/drivers/gpu/drm/i915/display/intel_vdsc.c
> > > >> > index 19cd9531c115..b05a96011d93 100644
> > > >> > --- a/drivers/gpu/drm/i915/display/intel_vdsc.c
> > > >> > +++ b/drivers/gpu/drm/i915/display/intel_vdsc.c
> > > >> > @@ -1161,10 +1161,6 @@ void intel_dsc_disable(const struct
> > > >> > intel_crtc_state
> > > >> > *old_crtc_state)
> > > >> >  	struct intel_crtc *crtc = to_intel_crtc(old_crtc_state-
> >uapi.crtc);
> > > >> >  	struct drm_i915_private *dev_priv = to_i915(crtc-
> >base.dev);
> > > >> >
> > > >> > -	if (!(old_crtc_state->dsc.compression_enable &&
> > > >> > -	      old_crtc_state->bigjoiner))
> > > >> > -		return;
> > > >> > -
> > > >> >  	intel_de_write(dev_priv, dss_ctl1_reg(old_crtc_state), 0);
> > > >> >  	intel_de_write(dev_priv, dss_ctl2_reg(old_crtc_state), 0);  }
> > > >> > --
> > > >> > 2.21.0.5.gaeb582a
> > > >> >
> > > >> > _______________________________________________
> > > >> > Intel-gfx mailing list
> > > >> > Intel-gfx at lists.freedesktop.org
> > > >> > https://lists.freedesktop.org/mailman/listinfo/intel-gfx
> > >
> > > --
> > > Jani Nikula, Intel Open Source Graphics Center