[Intel-gfx] [RFC v3] drm/i915: Select engines via class and instance in execbuffer2

[Chris Wilson]

On Thu, May 18, 2017 at 01:55:59PM +0300, Joonas Lahtinen wrote:
> On ke, 2017-05-17 at 16:40 +0100, Tvrtko Ursulin wrote:
> > From: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> > 
> > Building on top of the previous patch which exported the concept
> > of engine classes and instances, we can also use this instead of
> > the current awkward engine selection uAPI.
> > 
> > This is primarily interesting for the VCS engine selection which
> > is a) currently done via disjoint set of flags, and b) the
> > current I915_EXEC_BSD flags has different semantics depending on
> > the underlying hardware which is bad.
> > 
> > Proposed idea here is to reserve 16-bits of flags, to pass in
> > the engine class and instance (8 bits each), and a new flag
> > named I915_EXEC_CLASS_INSTACE to tell the kernel this new engine
> > selection API is in use.

Note this text doesn't describe the interface in v3.

> Would it make sense to use bitmask for future proofing? Then we could
> allow passing multiple options in the future.

No. The first use case has to be explicit control of engine. That's
orthogonal to asking to select any of a particular class.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre