Re: [PATCH 2/5] drm/i915/alpm: Allow LOBF only if window1 > alpm check_entry lines

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

On Fri, Nov 14, 2025 at 10:57:43AM +0530, Ankit Nautiyal wrote:
> LOBF must be disabled if the number of lines within Window 1 is not greater
> than ALPM_CTL[ALPM Entry Check]
> 
> v2: Consider the case where SCL is in the active region. (Ville)
> 
> Bspec:71041
> Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_alpm.c | 22 ++++++++++++++++++++++
>  1 file changed, 22 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_alpm.c b/drivers/gpu/drm/i915/display/intel_alpm.c
> index 98cbf5dde73b..686e4d13f864 100644
> --- a/drivers/gpu/drm/i915/display/intel_alpm.c
> +++ b/drivers/gpu/drm/i915/display/intel_alpm.c
> @@ -263,6 +263,23 @@ int intel_alpm_lobf_min_guardband(struct intel_crtc_state *crtc_state)
>  	return first_sdp_position + waketime_in_lines + crtc_state->set_context_latency;
>  }
>  
> +static bool intel_alpm_lobf_is_window1_sufficient(struct intel_crtc_state *crtc_state)
> +{
> +	struct drm_display_mode *adjusted_mode = &crtc_state->hw.adjusted_mode;
> +	int vblank = adjusted_mode->crtc_vtotal - adjusted_mode->crtc_vdisplay;
> +	int window1;
> +
> +	/*
> +	 * LOBF must be disabled if the number of lines within Window 1 is not
> +	 * greater than ALPM_CTL[ALPM Entry Check]
> +	 */
> +	window1 = vblank - min(vblank,
> +			       crtc_state->vrr.guardband +
> +			       crtc_state->set_context_latency);

Dunno why you have the min() here? guardband+SCL can never
exceed the total vblank length.

> +
> +	return window1 > crtc_state->alpm_state.check_entry_lines;
> +}
> +
>  void intel_alpm_lobf_compute_config_late(struct intel_dp *intel_dp,
>  					 struct intel_crtc_state *crtc_state)
>  {
> @@ -272,6 +289,11 @@ void intel_alpm_lobf_compute_config_late(struct intel_dp *intel_dp,
>  	if (!crtc_state->has_lobf)
>  		return;
>  
> +	if (!intel_alpm_lobf_is_window1_sufficient(crtc_state)) {
> +		crtc_state->has_lobf = false;
> +		return;
> +	}
> +
>  	/*
>  	 * LOBF can only be enabled if the time from the start of the SCL+Guardband
>  	 * window to the position of the first SDP is greater than the time it takes
> -- 
> 2.45.2

-- 
Ville Syrjälä
Intel