[Intel-gfx] [PATCH] drm/i915: Lock gmbus/aux mutexes while changing cdclk

[Chris Wilson]

Quoting Ville Syrjala (2020-02-27 19:39:54)
> From: Ville Syrjälä <ville.syrjala at linux.intel.com>
> 
> gmbus/aux may be clocked by cdclk, thus we should make sure no
> transfers are ongoing while the cdclk frequency is being changed.
> We do that by simply grabbing all the gmbus/aux mutexes. No one
> else should be holding any more than one of those at a time so
> the lock ordering here shouldn't matter.
> 
> Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_cdclk.c | 23 ++++++++++++++++++++++
>  1 file changed, 23 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_cdclk.c b/drivers/gpu/drm/i915/display/intel_cdclk.c
> index 0741d643455b..f69bf4a4eb1c 100644
> --- a/drivers/gpu/drm/i915/display/intel_cdclk.c
> +++ b/drivers/gpu/drm/i915/display/intel_cdclk.c
> @@ -1868,6 +1868,9 @@ static void intel_set_cdclk(struct drm_i915_private *dev_priv,
>                             const struct intel_cdclk_config *cdclk_config,
>                             enum pipe pipe)
>  {
> +       struct intel_encoder *encoder;
> +       unsigned int aux_mutex_lockclass = 0;
> +
>         if (!intel_cdclk_changed(&dev_priv->cdclk.hw, cdclk_config))
>                 return;
>  
> @@ -1876,8 +1879,28 @@ static void intel_set_cdclk(struct drm_i915_private *dev_priv,
>  
>         intel_dump_cdclk_config(cdclk_config, "Changing CDCLK to");
>  
> +       /*
> +        * Lock aux/gmbus while we change cdclk in case those
> +        * functions use cdclk. Not all platforms/ports do,
> +        * but we'll lock them all for simplicity.
> +        */
> +       mutex_lock(&dev_priv->gmbus_mutex);
> +       for_each_intel_dp(&dev_priv->drm, encoder) {
> +               struct intel_dp *intel_dp = enc_to_intel_dp(encoder);
> +
> +               mutex_lock_nested(&intel_dp->aux.hw_mutex,
> +                                 aux_mutex_lockclass++);

mutex_lock_nest_lock(&intel_dp->aux.hw_mutex, &dev_priv->gmbus_mutex);
?
-Chris