[PATCH 5/9] drm/i915/dmc: Reload pipe DMC state on TGL when enabling pipe A

[Shankar, Uma]

> -----Original Message-----
> From: Ville Syrjälä <ville.syrjala at linux.intel.com>
> Sent: Friday, June 13, 2025 7:40 PM
> To: Shankar, Uma <uma.shankar at intel.com>
> Cc: intel-gfx at lists.freedesktop.org; intel-xe at lists.freedesktop.org
> Subject: Re: [PATCH 5/9] drm/i915/dmc: Reload pipe DMC state on TGL when
> enabling pipe A
> 
> On Thu, Jun 12, 2025 at 08:32:16PM +0000, Shankar, Uma wrote:
> >
> >
> > > -----Original Message-----
> > > From: Intel-xe <intel-xe-bounces at lists.freedesktop.org> On Behalf Of
> > > Ville Syrjala
> > > Sent: Wednesday, June 11, 2025 9:23 PM
> > > To: intel-gfx at lists.freedesktop.org
> > > Cc: intel-xe at lists.freedesktop.org
> > > Subject: [PATCH 5/9] drm/i915/dmc: Reload pipe DMC state on TGL when
> > > enabling pipe A
> >
> > I guess its applicable for all pipes and not just limited to A.
> 
> Only pipe A has a DMC on these platforms.

Oh ok, got it.

> >
> > > From: Ville Syrjälä <ville.syrjala at linux.intel.com>
> > >
> > > On TGL/derivatives the entire pipe DMC state (program + MMIO) is
> > > lost when
> > > PG1 is disabled, and the main DMC does not restore any of it. Reload
> > > the state when enabling a pipe.
> >
> > It is just the TGL or any other platforms affected ?
> > Current change looks fine though.
> >
> > Reviewed-by: Uma Shankar <uma.shankar at intel.com>
> >
> > > The other option would be to not load the pipe DMC at all since it's
> > > only needed for "fast LACE" (which we don't use) on these platforms.
> > > But let's keep it around just in case we ever decide that "fast LACE" is
> something we want.
> >
> > I agree, it's good to keep it.
> >
> > > Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
> > > ---
> > >  drivers/gpu/drm/i915/display/intel_dmc.c | 9 +++++++++
> > >  1 file changed, 9 insertions(+)
> > >
> > > diff --git a/drivers/gpu/drm/i915/display/intel_dmc.c
> > > b/drivers/gpu/drm/i915/display/intel_dmc.c
> > > index 331db28039db..fd99c4645260 100644
> > > --- a/drivers/gpu/drm/i915/display/intel_dmc.c
> > > +++ b/drivers/gpu/drm/i915/display/intel_dmc.c
> > > @@ -599,6 +599,12 @@ static void dmc_load_program(struct
> > > intel_display *display,
> > >  	}
> > >  }
> > >
> > > +static bool need_pipedmc_load_program(struct intel_display *display) {
> > > +	/* On TGL/derivatives pipe DMC state is lost when PG1 is disabled */
> > > +	return DISPLAY_VER(display) == 12; }
> > > +
> > >  void intel_dmc_enable_pipe(struct intel_display *display, enum pipe pipe)  {
> > >  	enum intel_dmc_id dmc_id = PIPE_TO_DMC_ID(pipe); @@ -606,6 +612,9
> > > @@ void intel_dmc_enable_pipe(struct intel_display *display, enum pipe pipe)
> > >  	if (!is_valid_dmc_id(dmc_id) || !has_dmc_id_fw(display, dmc_id))
> > >  		return;
> > >
> > > +	if (need_pipedmc_load_program(display))
> > > +		dmc_load_program(display, dmc_id);
> > > +
> > >  	if (DISPLAY_VER(display) >= 20) {
> > >  		intel_de_write(display, PIPEDMC_INTERRUPT(pipe),
> > > pipedmc_interrupt_mask(display));
> > >  		intel_de_write(display, PIPEDMC_INTERRUPT_MASK(pipe),
> > > ~pipedmc_interrupt_mask(display));
> > > --
> > > 2.49.0
> >
> 
> --
> Ville Syrjälä
> Intel