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

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

On 11/14/2025 8:39 PM, Ville Syrjälä wrote:
> 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.


Hmm.. for PTL+ platforms, the SCL can be in vactive region, at that time 
SCL + guardband will become more than vblank.

In that case window1 would be 0.

I believed this is what you were pointing to in [1] or did I miss something.


[1]  https://lore.kernel.org/intel-xe/aQM_VK0wTlEiub9O@intel.com/


Regards,

Ankit




>
>> +
>> +	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