[Intel-gfx] [PATCH 2/3] drm/i915: Store engine mask in intel_gt

[Chris Wilson]

Quoting Tvrtko Ursulin (2019-10-16 14:31:45)
> 
> On 16/10/2019 14:03, Chris Wilson wrote:
> > Quoting Tvrtko Ursulin (2019-10-16 13:28:42)
> >> From: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> >>
> >> Medium term goal is to eliminate the i915->engine[] array and to get there
> >> we have recently introduced equivalent array in intel_gt. Now we need to
> >> migrate the code further towards this state.
> >>
> >> To allow for_each_engine_masked call sites to pass in gt instead of i915
> >> we need to have a copy of INTEL_INFO()->engine_mask in intel_gt.
> >>
> >> For this to work we also need to use engine->id as index when populating
> >> the gt->engine[] array.
> >>
> >> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> >> Cc: Chris Wilson <chris at chris-wilson.co.uk>
> >> ---
> >>   drivers/gpu/drm/i915/gt/intel_engine_user.c | 4 ++--
> >>   drivers/gpu/drm/i915/gt/intel_gt.c          | 5 +++++
> >>   drivers/gpu/drm/i915/gt/intel_gt.h          | 1 +
> >>   drivers/gpu/drm/i915/gt/intel_gt_types.h    | 4 ++++
> >>   drivers/gpu/drm/i915/i915_drv.c             | 2 ++
> >>   5 files changed, 14 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/drivers/gpu/drm/i915/gt/intel_engine_user.c b/drivers/gpu/drm/i915/gt/intel_engine_user.c
> >> index 77cd5de83930..099abae860ec 100644
> >> --- a/drivers/gpu/drm/i915/gt/intel_engine_user.c
> >> +++ b/drivers/gpu/drm/i915/gt/intel_engine_user.c
> >> @@ -183,8 +183,8 @@ static void add_legacy_ring(struct legacy_ring *ring,
> >>          if (unlikely(idx == -1))
> >>                  return;
> >>   
> >> -       GEM_BUG_ON(idx >= ARRAY_SIZE(ring->gt->engine));
> >> -       ring->gt->engine[idx] = engine;
> > 
> > This is used for the legacy uapi mapping. So we need to adjust the loop
> > in i915_gem_context.c::default_engines() to use engine->legacy_idx
> > instead of id. And all other users of engine->legacy_idx are now
> > backwards.
> 
> Hmmm that's evil.. I mean so well hidden dependency and contrary to 
> years of decoupling efforts. But I gather some mess is expected in these 
> circumstances. I'll update.

The decoupling effort is on the uAPI side, I do think the effort in
moving all the implicit legacy layout to a subset of the explicit user
controls is paying off nicely. The next goal was to remove gt->engine[],
so assumptions that it existed and engine->id was an index into it were
removed.
-Chris