Quoting Tvrtko Ursulin (2019-05-01 11:52:28)
> From: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
>
> Engine discovery query allows userspace to enumerate engines, probe their
> configuration features, all without needing to maintain the internal PCI
> ID based database.
>
> A new query for the generic i915 query ioctl is added named
> DRM_I915_QUERY_ENGINE_INFO, together with accompanying structure
> drm_i915_query_engine_info. The address of latter should be passed to the
> kernel in the query.data_ptr field, and should be large enough for the
> kernel to fill out all known engines as struct drm_i915_engine_info
> elements trailing the query.
>
> As with other queries, setting the item query length to zero allows
> userspace to query minimum required buffer size.
>
> Enumerated engines have common type mask which can be used to query all
> hardware engines, versus engines userspace can submit to using the execbuf
> uAPI.
>
> Engines also have capabilities which are per engine class namespace of
> bits describing features not present on all engine instances.
>
> v2:
> * Fixed HEVC assignment.
> * Reorder some fields, rename type to flags, increase width. (Lionel)
> * No need to allocate temporary storage if we do it engine by engine.
> (Lionel)
>
> v3:
> * Describe engine flags and mark mbz fields. (Lionel)
> * HEVC only applies to VCS.
>
> v4:
> * Squash SFC flag into main patch.
> * Tidy some comments.
>
> v5:
> * Add uabi_ prefix to engine capabilities. (Chris Wilson)
> * Report exact size of engine info array. (Chris Wilson)
> * Drop the engine flags. (Joonas Lahtinen)
> * Added some more reserved fields.
> * Move flags after class/instance.
>
> v6:
> * Do not check engine info array was zeroed by userspace but zero the
> unused fields for them instead.
>
> v7:
> * Simplify length calculation loop. (Lionel Landwerlin)
>
> v8:
> * Remove MBZ comments where not applicable.
> * Rename ABI flags to match engine class define naming.
> * Rename SFC ABI flag to reflect it applies to VCS and VECS.
> * SFC is wired to even _logical_ engine instances.
> * SFC applies to VCS and VECS.
> * HEVC is present on all instances on Gen11. (Tony)
> * Simplify length calculation even more. (Chris Wilson)
> * Move info_ptr assigment closer to loop for clarity. (Chris Wilson)
> * Use vdbox_sfc_access from runtime info.
> * Rebase for RUNTIME_INFO.
> * Refactor for lower indentation.
> * Rename uAPI class/instance to engine_class/instance to avoid C++
> keyword.
>
> v9:
> * Rebase for s/num_rings/num_engines/ in RUNTIME_INFO.
>
> v10:
> * Use new copy_query_item.
>
> v11:
> * Consolidate with struct i915_engine_class_instnace.
>
> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
> Cc: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> Cc: Jon Bloomfield <jon.bloomfield@xxxxxxxxx>
> Cc: Dmitry Rogozhkin <dmitry.v.rogozhkin@xxxxxxxxx>
> Cc: Lionel Landwerlin <lionel.g.landwerlin@xxxxxxxxx>
> Cc: Joonas Lahtinen <joonas.lahtinen@xxxxxxxxxxxxxxx>
> Cc: Tony Ye <tony.ye@xxxxxxxxx>
> Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@xxxxxxxxx> # v7
> Reviewed-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> # v7
> ---
> +/**
> + * struct drm_i915_engine_info
> + *
> + * Describes one engine and it's capabilities as known to the driver.
> + */
> +struct drm_i915_engine_info {
> + /** Engine class and instance. */
> + struct i915_engine_class_instance engine;
> +
> + /** Reserved field. */
> + __u32 rsvd0;
> +
> + /** Engine flags. */
> + __u64 flags;
Do you think we could do something like
BUILD_BUG_ON(!IS_ALIGNED(offsetof(*info, flags), sizeof(info->flags));
Will that work, and worthwhile? Maybe work into a
BUILD_BUG_ON(check_user_alignment(info, flags));
Reviewed-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
-Chris
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