Re: [PATCH v2 3/8] drm/i915/vrr: Account for TRANS_PUSH delay

["Nautiyal, Ankit K" <ankit.k.nautiyal@intel.com>]

On 2/8/2025 4:01 AM, Ville Syrjala wrote:
> From: Ville Syrjälä <ville.syrjala@linux.intel.com>
>
> When we send a push during vblank the TRANS_PUSH write happens
> at some point during a scanline, and the hardware picks it up
> on the next scanline. Thus there is up to one extra scanline
> of delay between the TRANS_PUSH write and the delayed vblank
> triggering. Account for that during intel_dsb_wait_vblank_delay()
> so that we are guaranteed to be past the delayed vblank before
> we trigger the completion interrupt for the commit.
>
> Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

Reviewed-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>


> ---
>   drivers/gpu/drm/i915/display/intel_dsb.c | 8 +++++++-
>   1 file changed, 7 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_dsb.c b/drivers/gpu/drm/i915/display/intel_dsb.c
> index f8bd6fad0c87..01e3bd385cac 100644
> --- a/drivers/gpu/drm/i915/display/intel_dsb.c
> +++ b/drivers/gpu/drm/i915/display/intel_dsb.c
> @@ -116,7 +116,13 @@ static int dsb_vblank_delay(struct intel_atomic_state *state,
>   		intel_pre_commit_crtc_state(state, crtc);
>   
>   	if (pre_commit_is_vrr_active(state, crtc))
> -		return intel_vrr_vblank_delay(crtc_state);
> +		/*
> +		 * When the push is sent during vblank it will trigger
> +		 * on the next scanline, hence we have up to one extra
> +		 * scanline until the delayed vblank occurs after
> +		 * TRANS_PUSH has been written.
> +		 */
> +		return intel_vrr_vblank_delay(crtc_state) + 1;
>   	else
>   		return intel_mode_vblank_delay(&crtc_state->hw.adjusted_mode);
>   }