[Intel-gfx] [PATCH v11] drm/i915: Engine discovery query

[Chris Wilson]

Quoting Tvrtko Ursulin (2019-05-01 11:52:28)
> From: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> 
> 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 at intel.com>
> Cc: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Jon Bloomfield <jon.bloomfield at intel.com>
> Cc: Dmitry Rogozhkin <dmitry.v.rogozhkin at intel.com>
> Cc: Lionel Landwerlin <lionel.g.landwerlin at intel.com>
> Cc: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
> Cc: Tony Ye <tony.ye at intel.com>
> Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin at intel.com> # v7
> Reviewed-by: Chris Wilson <chris at chris-wilson.co.uk> # 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 at chris-wilson.co.uk>
-Chris