[Intel-gfx] [PATCH] drm/i915/gem: Allow importing of shmemfs objects into any device

[Matthew Auld]

On Wed, 20 Jan 2021 at 15:40, Chris Wilson <chris at chris-wilson.co.uk> wrote:
>
> If we import a shmemfs object between devices, for example from
> Tigerlake to DG1, we can simply reuse the native object and its backing
> store.

Hmmm interesting, so does that include re-using the actual sg mapping
for the backing pages? Does that work out-of-the-box between different
devices assuming we have iommu enabled?

>
> Suggested-by: Imre Deak <imre.deak at intel.com>
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Matthew Auld <matthew.auld at intel.com>
> Cc: Imre Deak <imre.deak at intel.com>
> ---
>  drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c | 7 +++++++
>  1 file changed, 7 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c b/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c
> index 04e9c04545ad..4816f08c4009 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c
> @@ -242,6 +242,13 @@ struct drm_gem_object *i915_gem_prime_import(struct drm_device *dev,
>                          */
>                         return &i915_gem_object_get(obj)->base;
>                 }
> +
> +               /*
> +                * If the object is in plain system memory, we can reuse the
> +                * same backing store in any device.
> +                */
> +               if (i915_gem_object_is_shmem(obj))
> +                       return &i915_gem_object_get(obj)->base;
>         }
>
>         /* need to attach */
> --
> 2.20.1
>
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