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

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

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@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.

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

-- 
Ville Syrjälä
Intel