Re: [PATCH v2 20/56] drm/i915/ltphy: Add safegaurd when calculation HDMI FRL state

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] drm/i915/ltphy: Valid TMDS modes with FRL-like clocks get misidentified as FRL
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commit 24fcf65234b436b2c1d8a2379615e06c2dcf0888
Author: Suraj Kandpal <suraj.kandpal@intel.com>

drm/i915/ltphy: Add safegaurd when calculation HDMI FRL state

This commit adds a safeguard in intel_lt_phy_pll_calc_state() to skip the
HDMI TMDS dynamic PLL calculation when an HDMI FRL mode is in use. It
determines this by checking if the port clock matches an FRL rate.

> drm/i915/ltphy: Add safegaurd when calculation HDMI FRL state

This isn't a bug, but there is a typo (safegaurd) in the subject line.

> diff --git a/drivers/gpu/drm/i915/display/intel_lt_phy.c b/drivers/gpu/drm/i915/display/intel_lt_phy.c
> index 61bad87eefec2..0e2ebd550bc5e 100644
> --- a/drivers/gpu/drm/i915/display/intel_lt_phy.c
> +++ b/drivers/gpu/drm/i915/display/intel_lt_phy.c
> @@ -2042,7 +2042,8 @@ intel_lt_phy_pll_calc_state(struct intel_crtc_state *crtc_state,
>  		}
>  	}
>  
> -	if (intel_crtc_has_type(crtc_state, INTEL_OUTPUT_HDMI)) {
> +	if (intel_crtc_has_type(crtc_state, INTEL_OUTPUT_HDMI) &&
> +	    !intel_hdmi_is_frl(crtc_state->port_clock)) {

[Severity: Medium]
Does this logic mistakenly prevent the TMDS dynamic calculation for 300MHz
and 600MHz TMDS modes?

Looking at intel_hdmi_is_frl(), it only checks if the numeric clock rate
matches one of the FRL rates:

drivers/gpu/drm/i915/display/intel_hdmi.c:intel_hdmi_is_frl() {
	static const u32 rates[] = { 300000, 600000, 800000, 1000000, 1200000 };
	...
	for (i = 0; i < ARRAY_SIZE(rates); i++)
		if (intel_dpll_clock_matches(clock, rates[i]))
			return true;

	return false;
}

Since 300MHz and 600MHz can also be valid TMDS pixel clocks, a TMDS mode
with exactly these clock rates would cause intel_hdmi_is_frl() to return
true.

This would block the fallback intel_lt_phy_calculate_hdmi_state()
calculation for those valid TMDS modes.

Should this check verify the protocol state instead, for example by checking
if crtc_state->frl.enable is true?

>  		hw_state->ltpll.lane_count = crtc_state->lane_count;
>  		return intel_lt_phy_calculate_hdmi_state(&hw_state->ltpll,
>  							 crtc_state->port_clock);

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261012035806.3361439-1-ankit.k.nautiyal@intel.com?part=20