[Intel-gfx] [PATCH] drm/i915/tgl: Use refclk/2 as bypass frequency

[Ville Syrjälä]

On Thu, Sep 05, 2019 at 11:13:37AM -0700, Matt Roper wrote:
> Unlike gen11, which always ran at 50MHz when the cdclk PLL was disabled,
> TGL runs at refclk/2.  The 50MHz croclk/2 is only used by hardware
> during some power state transitions.
> 
> Bspec: 49201
> Cc: José Roberto de Souza <jose.souza at intel.com>
> Signed-off-by: Matt Roper <matthew.d.roper at intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_cdclk.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_cdclk.c b/drivers/gpu/drm/i915/display/intel_cdclk.c
> index 76f11d465e91..d3e56628af70 100644
> --- a/drivers/gpu/drm/i915/display/intel_cdclk.c
> +++ b/drivers/gpu/drm/i915/display/intel_cdclk.c
> @@ -1855,8 +1855,6 @@ static void icl_get_cdclk(struct drm_i915_private *dev_priv,
>  	u32 val;
>  	int div;
>  
> -	cdclk_state->bypass = 50000;
> -
>  	val = I915_READ(SKL_DSSM);
>  	switch (val & ICL_DSSM_CDCLK_PLL_REFCLK_MASK) {
>  	default:
> @@ -1873,6 +1871,11 @@ static void icl_get_cdclk(struct drm_i915_private *dev_priv,
>  		break;
>  	}
>  
> +	if (INTEL_GEN(dev_priv) >= 12)
> +		cdclk_state->bypass = cdclk_state->ref / 2;
> +	else
> +		cdclk_state->bypass = 50000;

Reviewed-by: Ville Syrjälä <ville.syrjala at linux.intel.com>

PS. I'd still like to see a icl_cdclk_pll_update() so I wouldn't have to
scratch my head why this looks so different to bxt/cnl code.

> +
>  	val = I915_READ(BXT_DE_PLL_ENABLE);
>  	if ((val & BXT_DE_PLL_PLL_ENABLE) == 0 ||
>  	    (val & BXT_DE_PLL_LOCK) == 0) {
> -- 
> 2.20.1
> 
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-- 
Ville Syrjälä
Intel