[Intel-gfx] [PATCH 1/6] drm/i915: Fix GEN8_MCR_SELECTOR programming

[Summers, Stuart]

On Wed, 2019-07-17 at 19:06 +0100, Tvrtko Ursulin wrote:
> From: Tvrtko Ursulin <tvrtko.ursulin at intel.com>

Not opposed to this exactly, but do we really need this patch if we're
just getting rid of this routine later in the series?

Thanks,
Stuart

> 
> fls returns bit positions starting from one for the lsb and the MCR
> register expects zero based (sub)slice addressing.
> 
> Incorrent MCR programming can have the effect of directing MMIO reads
> of
> registers in the 0xb100-0xb3ff range to invalid subslice returning
> zeroes
> instead of actual content.
> 
> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> Fixes: 1e40d4aea57b ("drm/i915/cnl: Implement
> WaProgramMgsrForCorrectSliceSpecificMmioReads")
> Reviewed-by: Chris Wilson <chris at chris-wilson.co.uk>
> ---
>  drivers/gpu/drm/i915/gt/intel_engine_cs.c | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/gt/intel_engine_cs.c
> b/drivers/gpu/drm/i915/gt/intel_engine_cs.c
> index c0bc9cb7f228..6f93caf7a5a1 100644
> --- a/drivers/gpu/drm/i915/gt/intel_engine_cs.c
> +++ b/drivers/gpu/drm/i915/gt/intel_engine_cs.c
> @@ -962,9 +962,14 @@ const char *i915_cache_level_str(struct
> drm_i915_private *i915, int type)
>  u32 intel_calculate_mcr_s_ss_select(struct drm_i915_private
> *dev_priv)
>  {
>  	const struct sseu_dev_info *sseu = &RUNTIME_INFO(dev_priv)-
> >sseu;
> +	unsigned int slice = fls(sseu->slice_mask) - 1;
> +	unsigned int subslice;
>  	u32 mcr_s_ss_select;
> -	u32 slice = fls(sseu->slice_mask);
> -	u32 subslice = fls(sseu->subslice_mask[slice]);
> +
> +	GEM_BUG_ON(slice >= ARRAY_SIZE(sseu->subslice_mask));
> +	subslice = fls(sseu->subslice_mask[slice]);
> +	GEM_BUG_ON(!subslice);
> +	subslice--;
>  
>  	if (IS_GEN(dev_priv, 10))
>  		mcr_s_ss_select = GEN8_MCR_SLICE(slice) |
-------------- next part --------------
A non-text attachment was scrubbed...
Name: smime.p7s
Type: application/x-pkcs7-signature
Size: 3270 bytes
Desc: not available
URL: <https://lists.freedesktop.org/archives/intel-gfx/attachments/20190717/3b23ee89/attachment.bin>