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

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

On Wed, Nov 09, 2022 at 09:37:24PM -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.
> 
> 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 | 2 ++
>  drivers/gpu/drm/i915/display/intel_cdclk.h | 1 +
>  2 files changed, 3 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_cdclk.c b/drivers/gpu/drm/i915/display/intel_cdclk.c
> index 8a9031012d74..91112d266763 100644
> --- a/drivers/gpu/drm/i915/display/intel_cdclk.c
> +++ b/drivers/gpu/drm/i915/display/intel_cdclk.c
> @@ -1962,6 +1962,8 @@ static bool intel_cdclk_can_crawl(struct drm_i915_private *dev_priv,
>  	if (!HAS_CDCLK_CRAWL(dev_priv))
>  		return false;
>  
> +	if (intel_pll_is_unknown(a->vco))
> +		return false;

I think this guy is only called from the atomic_check() path, so
this check shouldn't be needed here. Where we do need it is the
crawl check bxt_set_cdclk() since that is what gets called directly
from the sanitize() path with hw.vco=~0.

>  	/*
>  	 * The vco and cd2x divider will change independently
>  	 * from each, so we disallow cd2x change when crawling.
> diff --git a/drivers/gpu/drm/i915/display/intel_cdclk.h b/drivers/gpu/drm/i915/display/intel_cdclk.h
> index c674879a84a5..6eb83d806f11 100644
> --- a/drivers/gpu/drm/i915/display/intel_cdclk.h
> +++ b/drivers/gpu/drm/i915/display/intel_cdclk.h
> @@ -80,6 +80,7 @@ intel_atomic_get_cdclk_state(struct intel_atomic_state *state);
>  	to_intel_cdclk_state(intel_atomic_get_old_global_obj_state(state, &to_i915(state->base.dev)->display.cdclk.obj))
>  #define intel_atomic_get_new_cdclk_state(state) \
>  	to_intel_cdclk_state(intel_atomic_get_new_global_obj_state(state, &to_i915(state->base.dev)->display.cdclk.obj))
> +#define intel_pll_is_unknown(vco)	((vco) == ~0)
>  
>  int intel_cdclk_init(struct drm_i915_private *dev_priv);
>  
> -- 
> 2.25.1

-- 
Ville Syrjälä
Intel