[Intel-gfx] [PATCH v6 3/6] drm/i915/guc: Move the pin bias value from GuC to GGTT

[Michal Wajdeczko]

On Fri, 27 Jul 2018 12:29:15 +0200, Chris Wilson  
<chris at chris-wilson.co.uk> wrote:

> Quoting Jakub Bartmiński (2018-07-27 09:53:47)
>> diff --git a/drivers/gpu/drm/i915/i915_gem_gtt.c  
>> b/drivers/gpu/drm/i915/i915_gem_gtt.c
>> index d0acef299b9c..8ac5214b3648 100644
>> --- a/drivers/gpu/drm/i915/i915_gem_gtt.c
>> +++ b/drivers/gpu/drm/i915/i915_gem_gtt.c
>> @@ -2917,6 +2917,14 @@ int i915_gem_init_ggtt(struct drm_i915_private  
>> *dev_priv)
>>         struct drm_mm_node *entry;
>>         int ret;
>>
>> +       /*
>> +        * GuC requires the ring to be placed in Non-WOPCM memory. If  
>> GuC is not
>> +        * present or not in use we still need a small bias as ring  
>> wraparound
>> +        * at offset 0 sometimes hangs. No idea why.
>> +        */
>> +       ggtt->pin_bias = max_t(u32, I915_GTT_PAGE_SIZE,
>> +                               
>> intel_guc_wopcm_region_size(&dev_priv->guc));
>
> Hmm, it feels like this should fit in with ggtt_init_hw, but the current
> setup makes that impossible.
>
> intel_guc_wopcm_region_size() is a peculiar path to access
> dev_priv->wopcm.
>
> Do we not want something like intel_wopcm_lower_reserved_size()?

Earlier I was suggesting intel_guc_get_ggtt_pin_bias() as we should not
care how bias this is related to wopcm - only GuC should know that.

>
>> +/**
>> + * intel_guc_wopcm_region_size() - Get the size of the GuC region of  
>> WOPCM.
>> + * @guc: intel_guc structure.
>> + *
>> + * Returns:
>> + * 0 if GuC is not present or not in use.
>> + * Otherwise, the GuC WOPCM size.
>> + */
>> +u32 intel_guc_wopcm_region_size(struct intel_guc *guc)
>> +{
>> +       struct intel_wopcm *wopcm = &guc_to_i915(guc)->wopcm;
>> +
>> +       /* WOPCM must have already been partitioned */
>> +       GEM_BUG_ON(!wopcm->size);
>
> Unrelated bug-on, since what you want is a statement that
> intel_wopcm_init() was called and that doesn't provide it.

I guess GEM_BUG_ON(!wopcm->guc.size) should be better here.

Michal