Re: [PATCH v5 09/15] drm/i915/alpm: Modify LFPS cycle count for DP ALPM

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] Incorrect register bit mask selection for LFPS cycle count based on connector type instead of hardware IP version.
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--- Patch [9]: [PATCH v5 09/15] drm/i915/alpm: Modify LFPS cycle count for DP ALPM ---
commit f40607bd1107960e9e7fba56539c2f142247127f
Author: Animesh Manna <animesh.manna@intel.com>

drm/i915/alpm: Modify LFPS cycle count for DP ALPM
    
This commit modifies the display driver to set a minimum LFPS cycle
count of 16 for external DP on newer display IPs.

> diff --git a/drivers/gpu/drm/i915/display/intel_alpm.c b/drivers/gpu/drm/i915/display/intel_alpm.c
> index 98aa418a6ff77..890bf24885547 100644
> --- a/drivers/gpu/drm/i915/display/intel_alpm.c
> +++ b/drivers/gpu/drm/i915/display/intel_alpm.c
[ ... ]
> @@ -622,12 +635,21 @@ void intel_alpm_port_configure(struct intel_dp *intel_dp,
>  		return;
>  
>  	if (intel_alpm_is_alpm_aux_less(intel_dp, crtc_state)) {
> +		int lfps_cycle = get_lfps_cycle_count(crtc_state);
> +		u32 lfps_cycle_val;
> +
> +		if (intel_crtc_has_type(crtc_state, INTEL_OUTPUT_EDP))
> +			lfps_cycle_val = PORT_ALPM_LFPS_CTL_LFPS_CYCLE_COUNT(lfps_cycle);
> +		else
> +			lfps_cycle_val = PORT_ALPM_LFPS_CTL_LFPS_CYCLE_COUNT_XE3LPD(lfps_cycle);
                ^^^^

[Severity: Medium]
Does this code incorrectly conflate the sink type with the display IP version?

In intel_alpm_port_configure(), branching on the connector type
(INTEL_OUTPUT_EDP) rather than the hardware IP version causes eDP panels on
Xe3LPD to be programmed using the legacy 4-bit register mask instead of the
expanded 7-bit Xe3LPD mask.

While the current default value for eDP (10 cycles) happens to fit within the
lower 4 bits, if the eDP LFPS cycle count is ever tuned to a value > 22, the
legacy 4-bit mask will truncate it and could corrupt the hardware configuration.

Should this logic check the display version instead of the output type?

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Sashiko AI review · https://sashiko.dev/#/patchset/20260825054536.3455704-1-animesh.manna@intel.com?part=9