[Intel-gfx] [PATCH v3 1/2] drm/i915: Don't use stolen memory for ring buffers with LLC

[Ceraolo Spurio, Daniele]

On 2/15/2023 5:11 PM, John.C.Harrison at Intel.com wrote:
> From: John Harrison <John.C.Harrison at Intel.com>
>
> Direction from hardware is that stolen memory should never be used for
> ring buffer allocations on platforms with LLC. There are too many
> caching pitfalls due to the way stolen memory accesses are routed. So
> it is safest to just not use it.
>
> Signed-off-by: John Harrison <John.C.Harrison at Intel.com>
> Fixes: c58b735fc762 ("drm/i915: Allocate rings from stolen")
> Cc: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
> Cc: Jani Nikula <jani.nikula at linux.intel.com>
> Cc: Rodrigo Vivi <rodrigo.vivi at intel.com>
> Cc: Tvrtko Ursulin <tvrtko.ursulin at linux.intel.com>
> Cc: intel-gfx at lists.freedesktop.org
> Cc: <stable at vger.kernel.org> # v4.9+

Reviewed-by: Daniele Ceraolo Spurio <daniele.ceraolospurio at intel.com>

Daniele

> ---
>   drivers/gpu/drm/i915/gt/intel_ring.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/i915/gt/intel_ring.c b/drivers/gpu/drm/i915/gt/intel_ring.c
> index 15ec64d881c44..fb1d2595392ed 100644
> --- a/drivers/gpu/drm/i915/gt/intel_ring.c
> +++ b/drivers/gpu/drm/i915/gt/intel_ring.c
> @@ -116,7 +116,7 @@ static struct i915_vma *create_ring_vma(struct i915_ggtt *ggtt, int size)
>   
>   	obj = i915_gem_object_create_lmem(i915, size, I915_BO_ALLOC_VOLATILE |
>   					  I915_BO_ALLOC_PM_VOLATILE);
> -	if (IS_ERR(obj) && i915_ggtt_has_aperture(ggtt))
> +	if (IS_ERR(obj) && i915_ggtt_has_aperture(ggtt) && !HAS_LLC(i915))
>   		obj = i915_gem_object_create_stolen(i915, size);
>   	if (IS_ERR(obj))
>   		obj = i915_gem_object_create_internal(i915, size);