Re: [PATCH 1/2] drm/i915/cnl: Implement WaProgramMgsrForCorrectSliceSpecificMmioReads

[Chris Wilson <chris@chris-wilson.co.uk>]

Quoting Yunwei Zhang (2018-03-19 21:50:07)
> WaProgramMgsrForCorrectSliceSpecificMmioReads dictate that before any MMIO
> read into Slice/Subslice specific registers, MCR packet control
> register(0xFDC) needs to be programmed to point to any enabled
> slice/subslice pair. Otherwise, incorrect value will be returned.
> 
> However, that means each subsequent MMIO read will be forwarded to a
> specific slice/subslice combination as read is unicast. This is OK since
> slice/subslice specific register values are consistent in almost all cases
> across slice/subslice. There are rare occasions such as INSTDONE that this
> value will be dependent on slice/subslice combo, in such cases, we need to
> program 0xFDC and recover this after. This is already covered by
> read_subslice_reg for INSTDONE.
> 
> Also, 0xFDC will lose its information after TDR/engine reset/power state
> change.
> 
> Signed-off-by: Yunwei Zhang <yunwei.zhang@intel.com>
> Cc: Oscar Mateo <oscar.mateo@intel.com>
> Cc: Michel Thierry <michel.thierry@intel.com>
> Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
> ---
>  drivers/gpu/drm/i915/intel_engine_cs.c | 43 ++++++++++++++++++++++++++++++++--
>  1 file changed, 41 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_engine_cs.c b/drivers/gpu/drm/i915/intel_engine_cs.c
> index a2b1e9e..bc8fed7 100644
> --- a/drivers/gpu/drm/i915/intel_engine_cs.c
> +++ b/drivers/gpu/drm/i915/intel_engine_cs.c
> @@ -781,6 +781,29 @@ const char *i915_cache_level_str(struct drm_i915_private *i915, int type)
>         }
>  }
>  
> +static u32 calculate_mcr(u32 mcr, struct drm_i915_private *dev_priv)
> +{
> +       const struct sseu_dev_info *sseu = &(INTEL_INFO(dev_priv)->sseu);

INTEL_SSEU(dev_priv);

> +       u32 slice = find_last_bit((unsigned long *)&(sseu->slice_mask),
> +                                  sizeof(sseu->slice_mask));
> +       u32 subslice = find_last_bit((unsigned long *)&(sseu->subslice_mask[slice]),
> +                                     sizeof(sseu->subslice_mask[0]));

You seem to have mispelt fls().

Or send a patch to convert find_last_bit() into fls() for known small
sizes.
-Chris
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