Re: [PATCH v4 11/13] drm/i915/display: Evade scanline 0 as well if PSR1 or PSR2 is enabled

["Hogander, Jouni" <jouni.hogander@intel.com>]

On Fri, 2025-01-24 at 13:39 +0200, Ville Syrjälä wrote:
> On Fri, Jan 24, 2025 at 12:56:22PM +0200, Jouni Högander wrote:
> > PIPEDSL is reading as 0 when in SRDENT(PSR1) or DEEP_SLEEP(PSR2).
> > On
> > wake-up scanline counting starts from vblank_start - 1. We don't
> > know if
> > wake-up is already ongoing when evasion starts. In worst case
> > PIPEDSL could
> > start reading valid value right after checking the scanline. In
> > this
> > scenario we wouldn't have enough time to write all registers. To
> > tackle
> > this evade scanline 0 as well. As a drawback we have 1 frame delay
> > in flip
> > when waking up.
> > 
> > Signed-off-by: Jouni Högander <jouni.hogander@intel.com>
> > ---
> >  drivers/gpu/drm/i915/display/intel_dsb.c | 12 ++++++++++++
> >  1 file changed, 12 insertions(+)
> > 
> > diff --git a/drivers/gpu/drm/i915/display/intel_dsb.c
> > b/drivers/gpu/drm/i915/display/intel_dsb.c
> > index bb77ded8bf726..914f0be4491c4 100644
> > --- a/drivers/gpu/drm/i915/display/intel_dsb.c
> > +++ b/drivers/gpu/drm/i915/display/intel_dsb.c
> > @@ -528,6 +528,18 @@ void intel_dsb_vblank_evade(struct
> > intel_atomic_state *state,
> >  	int latency = intel_usecs_to_scanlines(&crtc_state-
> > >hw.adjusted_mode, 20);
> >  	int start, end;
> >  
> > +	/*
> > +	 * PIPEDSL is reading as 0 when in SRDENT(PSR1) or
> > DEEP_SLEEP(PSR2). On
> > +	 * wake-up scanline counting starts from vblank_start - 1.
> > We don't know
> > +	 * if wake-up is already ongoing when evasion starts. In
> > worst case
> > +	 * PIPEDSL could start reading valid value right after
> > checking the
> > +	 * scanline. In this scenario we wouldn't have enough time
> > to write all
> > +	 * registers. To tackle this evade scanline 0 as well. As
> > a drawback we
> > +	 * have 1 frame delay in flip when waking up.
> > +	 */
> > +	if (crtc_state->has_psr && !crtc_state->has_panel_replay)
> 
> What's the deal with panel replay here?

I couldn't see PIPEDSL returning 0 when using Panel Replay. Even on
same setup with PSR I saw it, but with PR I couldn't see.

> 
> > +		intel_dsb_wait_scanline_out(state, dsb, 0, 0);
> 
> This needs to be a raw
> intel_dsb_emit_wait_dsl(dsb, DSB_OPCODE_WAIT_DSL_OUT, 0, 0)
> because we need to evade the hw scanline 0. What the software
> thinks is scanline 0 is a bit different (see scanline_offset).

Ok, I will change this.

BR,

Jouni Högander

> 
> > +
> >  	if (pre_commit_is_vrr_active(state, crtc)) {
> >  		int vblank_delay =
> > intel_vrr_vblank_delay(crtc_state);
> >  
> > -- 
> > 2.43.0
>