[Intel-gfx] [PATCH v7] drm/i915: Engine discovery query

[Chris Wilson]

Quoting Tvrtko Ursulin (2018-10-05 09:34:35)
> 
> On 04/10/2018 15:32, Joonas Lahtinen wrote:
> > Some comments below, mostly related to trying to keep the uapi header
> > nice and tidy.
> > 
> > Quoting Tvrtko Ursulin (2018-10-04 14:32:48)
> >> @@ -1747,6 +1748,52 @@ struct drm_i915_query_topology_info {
> >>          __u8 data[];
> >>   };
> >>   
> >> +/**
> >> + * struct drm_i915_engine_info
> >> + *
> >> + * Describes one engine known to the driver, whether or not it is an user-
> >> + * accessible or hardware only engine, and what are it's capabilities where
> >> + * applicable.
> >> + */
> >> +struct drm_i915_engine_info {
> >> +       /** Engine class as in enum drm_i915_gem_engine_class. */
> >> +       __u16 class;
> >> +
> >> +       /** Engine instance number. */
> >> +       __u16 instance;
> >> +
> >> +       /** Reserved field must be cleared to zero. */
> >> +       __u32 rsvd0;
> > 
> > u32 class, u32 instance just to put the padding to good use?
> 
> There is some attractiveness to lose the padding, but I think in general 
> we trashed it out to be u16:u16. So it is a question of consistency vs 
> elegance and I give preference to consistency.
> 
> Chris, is your recollection also that we said u16:u16 for class:instance 
> in all uAPI?

Yes, that is the conclusion we came to. I've changed my uABI to u16:u16
as well.

u8:u8 too tight, u32:u32 very unlikely. u16 is goldilocks.
-Chris