[Intel-gfx] [RFC v4 1/2] drm/i915: Engine discovery uAPI

[Chris Wilson]

Quoting Tvrtko Ursulin (2017-06-26 16:47:41)
> From: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> 
> Engine discovery uAPI allows userspace to probe for engine
> configuration and features without needing to maintain the
> internal PCI id based database.
> 
> This enables removal of code duplications across userspace
> components.
> 
> Probing is done via the new DRM_IOCTL_I915_GEM_ENGINE_INFO ioctl
> which returns the number and information on the specified engine
> class.
> 
> Currently only general engine configuration and HEVC feature of
> the VCS engine can be probed but the uAPI is designed to be
> generic and extensible.
> 
> Code is based almost exactly on the earlier proposal on the
> topic by Jon Bloomfield. Engine class and instance refactoring
> made recently by Daniele Ceraolo Spurio enabled this to be
> implemented in an elegant fashion.
> 
> To probe configuration userspace sets the engine class it wants
> to query (struct drm_i915_gem_engine_info) and provides an array
> of drm_i915_engine_info structs which will be filled in by the
> driver. Userspace also has to tell i915 how many elements are in
> the array, and the driver will report back the total number of
> engine instances in any case.

Include psuedo code to first show how to do the multipass query followed
by an example hooking it to execbuf.
-Chris