[PATCH v4 12/13] drm/i915/display: Ensure we have "Frame Change" event in DSB commit

[Hogander, Jouni]

On Fri, 2025-01-24 at 13:43 +0200, Ville Syrjälä wrote:
> On Fri, Jan 24, 2025 at 12:56:23PM +0200, Jouni Högander wrote:
> > We may have commit which doesn't have any non-arming plane register
> > writes. In that case there aren't "Frame Change" event before DSB
> > vblank
> > evasion which hangs as PIPEDSL register is reading as 0 when PSR
> > state is
> > SRDENT(PSR1) or DEEP_SLEEP(PSR2). Handle this by adding dummy write
> > triggering the "Frame Change" event.
> > 
> > Signed-off-by: Jouni Högander <jouni.hogander at intel.com>
> > ---
> >  drivers/gpu/drm/i915/display/intel_display.c | 10 ++++++++++
> >  1 file changed, 10 insertions(+)
> > 
> > diff --git a/drivers/gpu/drm/i915/display/intel_display.c
> > b/drivers/gpu/drm/i915/display/intel_display.c
> > index a189aa437d972..cd7e960bd29f1 100644
> > --- a/drivers/gpu/drm/i915/display/intel_display.c
> > +++ b/drivers/gpu/drm/i915/display/intel_display.c
> > @@ -7666,6 +7666,7 @@ static void intel_atomic_dsb_finish(struct
> > intel_atomic_state *state,
> >  		intel_atomic_get_old_crtc_state(state, crtc);
> >  	struct intel_crtc_state *new_crtc_state =
> >  		intel_atomic_get_new_crtc_state(state, crtc);
> > +	struct intel_display *display = to_intel_display(crtc);
> >  
> >  	if (!new_crtc_state->hw.active)
> >  		return;
> > @@ -7708,6 +7709,15 @@ static void intel_atomic_dsb_finish(struct
> > intel_atomic_state *state,
> >  		intel_crtc_planes_update_noarm(new_crtc_state-
> > >dsb_commit,
> >  					       state, crtc);
> >  
> > +		/*
> > +		 * Ensure we have "Frame Change" event when PSR
> > state is
> > +		 * SRDENT(PSR1) or DEEP_SLEEP(PSR2). Otherwise DSB
> > vblank
> > +		 * evasion hangs as PIPEDSL is reading as 0.
> > +		 */
> > +		if (new_crtc_state->has_psr && !new_crtc_state-
> > >has_panel_replay)
> > +			intel_de_write_dsb(display,
> > new_crtc_state->dsb_commit,
> > +					   CURSURFLIVE(display,
> > crtc->pipe), 0);
> 
> I don't really want to see the low level detais right here.
> So we should probably should stuff this into some kind of 
> intel_dsb_ensure_psr_frame_change() function or something
> along those lines.

Ok, I will write such function.

BR,

Jouni Högander
> 
> > +
> >  		intel_dsb_vblank_evade(state, new_crtc_state-
> > >dsb_commit);
> >  
> >  		if (intel_crtc_needs_color_update(new_crtc_state))
> > -- 
> > 2.43.0
>