Re: [Intel-gfx] [PATCH] drm/i915/gen11: use ffs for minconfig slice/subslice

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

On Fri, Jun 11, 2021 at 08:04:09PM +0530, Tejas Upadhyay wrote:
> w/a on gen11 platforms not working as expected and causing
> more harm on the RC6 flow. Because of subslice steering
> disturbance w/a read is failing. By using ffs we can default
> steering of slice/sublice to minconfig hence w/a will pass
> and any warns will go away.
> 
> Fixes: fb899dd8ea9c ("drm/i915: Apply Wa_1406680159:icl,ehl as an engine workaround")
> Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
> Cc: Matt Roper <matthew.d.roper@intel.com>
> Signed-off-by: Tejas Upadhyay <tejaskumarx.surendrakumar.upadhyay@intel.com>
> ---
>  drivers/gpu/drm/i915/gt/intel_workarounds.c | 14 +++++++++++---
>  drivers/gpu/drm/i915/intel_pm.c             | 10 +++++++---
>  2 files changed, 18 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/gt/intel_workarounds.c b/drivers/gpu/drm/i915/gt/intel_workarounds.c
> index b62d1e31a645..68b14141088a 100644
> --- a/drivers/gpu/drm/i915/gt/intel_workarounds.c
> +++ b/drivers/gpu/drm/i915/gt/intel_workarounds.c
> @@ -991,13 +991,21 @@ wa_init_mcr(struct drm_i915_private *i915, struct i915_wa_list *wal)
>  		l3_en = ~0;
>  	}
>  
> -	slice = fls(sseu->slice_mask) - 1;
> -	subslice = fls(l3_en & intel_sseu_get_subslices(sseu, slice));
> +	if (GRAPHICS_VER(i915) == 11) {
> +		slice = ffs(sseu->slice_mask) - 1;
> +		subslice = ffs(l3_en & intel_sseu_get_subslices(sseu, slice));
> +	} else {
> +		slice = fls(sseu->slice_mask) - 1;
> +		subslice = fls(l3_en & intel_sseu_get_subslices(sseu, slice));
> +	}
>  	if (!subslice) {
>  		drm_warn(&i915->drm,
>  			 "No common index found between subslice mask %x and L3 bank mask %x!\n",
>  			 intel_sseu_get_subslices(sseu, slice), l3_en);
> -		subslice = fls(l3_en);
> +		if (GRAPHICS_VER(i915) == 11)
> +			subslice = ffs(l3_en);
> +		else
> +			subslice = fls(l3_en);
>  		drm_WARN_ON(&i915->drm, !subslice);
>  	}
>  	subslice--;
> diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
> index 45fefa0ed160..d1352ec3546a 100644
> --- a/drivers/gpu/drm/i915/intel_pm.c
> +++ b/drivers/gpu/drm/i915/intel_pm.c
> @@ -4049,9 +4049,13 @@ skl_ddb_entry_for_slices(struct drm_i915_private *dev_priv, u8 slice_mask,
>  		ddb->end = 0;
>  		return;
>  	}
> -
> -	ddb->start = (ffs(slice_mask) - 1) * slice_size;
> -	ddb->end = fls(slice_mask) * slice_size;
> +	if (GRAPHICS_VER(dev_priv) == 11) {
> +		ddb->start = (fls(slice_mask) - 1) * slice_size;
> +		ddb->end = ffs(slice_mask) * slice_size;
> +	} else {
> +		ddb->start = (ffs(slice_mask) - 1) * slice_size;
> +		ddb->end = fls(slice_mask) * slice_size;
> +	}

This code has nothing to do with GT slices.

>  
>  	WARN_ON(ddb->start >= ddb->end);
>  	WARN_ON(ddb->end > INTEL_INFO(dev_priv)->dbuf.size);
> -- 
> 2.31.1
> 
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-- 
Ville Syrjälä
Intel
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