Re: [PATCH 2/4] drm/i915/psr: Perform vblank evasion on async flip as well for PSR

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

On Tue, Nov 25, 2025 at 08:32:51AM +0200, Jouni Högander wrote:
> PSR2_MAN_TRK_CTL[SF Continuous full frame] is sampled on the rising edge of
> delayed vblank. SW must ensure this bit is not changing around that. Due to
> this PSR2 Selective Fetch needs vblank evasion.
> 
> Currently vblank evasion is not done on async flip. Perform it in case
> required by PSR.
> 
> Bspec: 50424
> Signed-off-by: Jouni Högander <jouni.hogander@intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_crtc.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_crtc.c b/drivers/gpu/drm/i915/display/intel_crtc.c
> index 153ff4b4b52c..42c4ce07f8c0 100644
> --- a/drivers/gpu/drm/i915/display/intel_crtc.c
> +++ b/drivers/gpu/drm/i915/display/intel_crtc.c
> @@ -433,7 +433,8 @@ static bool intel_crtc_needs_vblank_work(const struct intel_crtc_state *crtc_sta
>  		(intel_crtc_needs_color_update(crtc_state) &&
>  		 !HAS_DOUBLE_BUFFERED_LUT(display)) &&
>  		!intel_color_uses_dsb(crtc_state) &&
> -		!crtc_state->use_dsb;
> +		!crtc_state->use_dsb &&
> +		!crtc_state->do_async_flip;
>  }
>  
>  static void intel_crtc_vblank_work(struct kthread_work *base)
> @@ -539,7 +540,8 @@ void intel_pipe_update_start(struct intel_atomic_state *state,
>  	if (new_crtc_state->do_async_flip) {
>  		intel_crtc_prepare_vblank_event(new_crtc_state,
>  						&crtc->flip_done_event);
> -		return;
> +		if (!intel_psr_needs_evasion(new_crtc_state))
> +			return;

I don't think we want hack this into such low level code. We
anyway convert the first async flip to a sync flip (see
intel_plane_do_async_flip()), so that's when you should disable
selective fetch, and keep it disabled afterwards as long as
async flips are being requested for the plane by userspace.

The problem is that uapi.async_flip is ephemeral, so you can't
just check for that. I think what we need is a way to track
which planes have been requested to do async flips. We almost 
have that with the async_flip_planes bitmask, and I think we
can make it do exactly what we want by just dropping the
need_async_flip_toggle_wa check from 
intel_plane_atomic_calc_changes(). That should be safe since
all places that currently use the bitmask also check for
need_async_flip_toggle_wa.

The alternative would be to track the uapi async flip requests
in a separate bitmask. That might be a bit more optimal in that
we wouldn't clear the bit from there when some other plane
or the pipe itself needs a sync update while the plane is already
performing async flips. But not having that just means you'll
end up toggling selective fetch back on and the off again when
a sync update intervenes a stream of async flips.

Oh, and needs_async_flip_vtd_wa() should probably also use
the bitmask rather than looking at uapi.async_flip.

>  	}
>  
>  	if (intel_crtc_needs_vblank_work(new_crtc_state))
> -- 
> 2.43.0

-- 
Ville Syrjälä
Intel