Re: [Intel-gfx] [PATCH] drm/i915/display: Add missing checks for cdclk crawling

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Fri, Nov 11, 2022 at 11:26:02AM -0800, Anusha Srivatsa wrote:
> cdclk_sanitize() function was written assuming vco was a signed integer.
> vco gets assigned to -1 (essentially ~0) for the case where PLL
> might be enabled and vco is not a frequency that will ever
> get used. In such a scenario the right thing to do is disable the
> PLL and re-enable it again with a valid frequency.
> However the vco is declared as a unsigned variable.
> With the above assumption, driver takes crawl path when not needed.
> Add explicit check to not crawl in the case of an invalid PLL.
> 
> v2: Move the check from .h to .c (MattR)
> - Move check to bxt_set_cdclk() instead of
> intel_modeset_calc_cdclk() which is directly in
> the path of the sanitize() function (Ville)
> 
> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> Cc: Matt Roper <matthew.d.roper@intel.com>
> Suggested-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> Signed-off-by: Anusha Srivatsa <anusha.srivatsa@intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_cdclk.c | 13 ++++++++++++-
>  1 file changed, 12 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_cdclk.c b/drivers/gpu/drm/i915/display/intel_cdclk.c
> index 8a9031012d74..2d9b7ba58358 100644
> --- a/drivers/gpu/drm/i915/display/intel_cdclk.c
> +++ b/drivers/gpu/drm/i915/display/intel_cdclk.c
> @@ -1716,6 +1716,16 @@ static void dg2_cdclk_squash_program(struct drm_i915_private *i915,
>  	intel_de_write(i915, CDCLK_SQUASH_CTL, squash_ctl);
>  }
>  
> +static bool cdclk_pll_is_unknown(unsigned int vco)
> +{
> +	/*
> +	 * Ensure driver does not take the crawl path for the
> +	 * case when the vco is set to ~0 in the
> +	 * sanitize path.
> +	 */
> +	return (vco == ~0);

Pointless parens.

> +}
> +
>  static void bxt_set_cdclk(struct drm_i915_private *dev_priv,
>  			  const struct intel_cdclk_config *cdclk_config,
>  			  enum pipe pipe)
> @@ -1748,7 +1758,8 @@ static void bxt_set_cdclk(struct drm_i915_private *dev_priv,
>  		return;
>  	}
>  
> -	if (HAS_CDCLK_CRAWL(dev_priv) && dev_priv->display.cdclk.hw.vco > 0 && vco > 0) {
> +	if (HAS_CDCLK_CRAWL(dev_priv) && dev_priv->display.cdclk.hw.vco > 0 && vco > 0 &&
> +	    (!cdclk_pll_is_unknown(dev_priv->display.cdclk.hw.vco))) {

More pointless parens

With those removed
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

Though I think we should probably add the pll_is_enabled()
helper too, just make the code a bit more self explanatory.

>  		if (dev_priv->display.cdclk.hw.vco != vco)
>  			adlp_cdclk_pll_crawl(dev_priv, vco);
>  	} else if (DISPLAY_VER(dev_priv) >= 11)
> -- 
> 2.25.1

-- 
Ville Syrjälä
Intel