Re: [PATCH] drm/i915/display: Calculate crtc clock rate based on PLL parameters

[Imre Deak <imre.deak@intel.com>]

On Thu, May 02, 2024 at 04:17:16PM +0300, Mika Kahola wrote:
> With HDMI monitors we bumped up a case where the crtc clock rate
> caused a mismatch on state verification. This was due to
> assumption that the SW clock rate from PLL structure would match
> the calculated counterpart from HW. This is not necessarily always
> the case and therefore we would actually need to recalculate the
> clock rate from SW PLL parameters. Then these SW and HW crtc clock
> rates can be compared with each other.
> 
> The patch recalculates the crtc clock rate for SW state based on
> SW PLL parameters and compares the crtc clock rate calculated
> from the parameters found from the HW.
> 
> Signed-off-by: Mika Kahola <mika.kahola@intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_cx0_phy.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_cx0_phy.c b/drivers/gpu/drm/i915/display/intel_cx0_phy.c
> index 8e3b13884bb8..89a195917179 100644
> --- a/drivers/gpu/drm/i915/display/intel_cx0_phy.c
> +++ b/drivers/gpu/drm/i915/display/intel_cx0_phy.c
> @@ -3078,9 +3078,10 @@ static void intel_c20pll_state_verify(const struct intel_crtc_state *state,
>  	const struct intel_c20pll_state *mpll_sw_state = &state->dpll_hw_state.cx0pll.c20;
>  	bool sw_use_mpllb = intel_c20phy_use_mpllb(mpll_sw_state);
>  	bool hw_use_mpllb = intel_c20phy_use_mpllb(mpll_hw_state);
> +	int clock = intel_c20pll_calc_port_clock(encoder, mpll_sw_state);
>  	int i;
>  
> -	I915_STATE_WARN(i915, mpll_hw_state->clock != mpll_sw_state->clock,
> +	I915_STATE_WARN(i915, mpll_hw_state->clock != clock,

There is a corresponding check already in the encoder state checker,
which is more approriate, since it compares the calculated PLL clock
against the - adjusted - crtc port clock and I think that's the only
place all other platforms check this. In any case the above check
looks correct:

Reviewed-by: Imre Deak <imre.deak@intel.com>

>  			"[CRTC:%d:%s] mismatch in C20: Register CLOCK (expected %d, found %d)",
>  			crtc->base.base.id, crtc->base.name,
>  			mpll_sw_state->clock, mpll_hw_state->clock);
> -- 
> 2.34.1
>