Re: [Intel-gfx] [PATCH v2 20/20] drm/i915: Check slice mask for holes

["Lisovskiy, Stanislav" <stanislav.lisovskiy@intel.com>]

On Tue, 2020-02-25 at 19:11 +0200, Ville Syrjala wrote:
> From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> 
> Make sure the dbuf slice mask for any individual pipe has no
> holes between the slices.
> 
> Cc: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>
> Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> ---
>  drivers/gpu/drm/i915/intel_pm.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/intel_pm.c
> b/drivers/gpu/drm/i915/intel_pm.c
> index 7edac506d343..fa39ab0b1223 100644
> --- a/drivers/gpu/drm/i915/intel_pm.c
> +++ b/drivers/gpu/drm/i915/intel_pm.c
> @@ -3827,6 +3827,14 @@ static int intel_dbuf_slice_size(struct
> drm_i915_private *dev_priv)
>  		INTEL_INFO(dev_priv)->num_supported_dbuf_slices;
>  }
>  
> +static bool bitmask_is_contiguous(unsigned int bitmask)
> +{
> +	if (bitmask)
> +		bitmask >>= ffs(bitmask) - 1;
> +
> +	return is_power_of_2(bitmask + 1);
> +}
> +

Well, I guess we just don't trust BSpec tables here :)

Shouldn't this be already taken care of by the actual tables, which we
anyway seem have to encode "as is".

Moreover, I wouldn't even be sure that one day, they won't come up
with that you can have gaps for those, anyway currently
we don't have them according to current tables

Stan

>  static void
>  skl_ddb_entry_for_slices(struct drm_i915_private *dev_priv, u8
> slice_mask,
>  			 struct skl_ddb_entry *ddb)
> @@ -3844,6 +3852,7 @@ skl_ddb_entry_for_slices(struct
> drm_i915_private *dev_priv, u8 slice_mask,
>  
>  	WARN_ON(ddb->start >= ddb->end);
>  	WARN_ON(ddb->end > intel_dbuf_size(dev_priv));
> +	WARN_ON(!bitmask_is_contiguous(slice_mask));
>  }
>  
>  static unsigned int intel_crtc_ddb_weight(const struct
> intel_crtc_state *crtc_state)
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