[Intel-gfx] [PATCH v2 2/9] drm/i915: Force the switch to the i915->kernel_context

[Chris Wilson]

Quoting Mika Kuoppala (2017-11-03 14:03:25)
> Chris Wilson <chris at chris-wilson.co.uk> writes:
> 
> > In the next few patches, we will have a hard requirement that we emit a
> > context-switch to the perma-pinned i915->kernel_context (so that we can
> > save the HW state using that context-switch). As the first context
> > itself may be classed as a kernel context, we want to be explicit in our
> > comparison. For an extra-layer of finesse, we can check the last
> > unretired context on the engine; as well as the last retired context
> > when idle.
> >
> > v2: verbose verbosity
> > v3: Always force the switch, even when the engine is idle, and update
> > the assert that this happens before suspend.
> >
> > Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> > Cc: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
> > Reviewed-by: Joonas Lahtinen <joonas.lahtinen at linux.intel.com> #v1
> > ---
> >  drivers/gpu/drm/i915/i915_gem.c        | 10 ++++++----
> >  drivers/gpu/drm/i915/intel_engine_cs.c | 26 ++++++++++++++++++++++++--
> >  2 files changed, 30 insertions(+), 6 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> > index 9470ba0c1930..fe312ab3b664 100644
> > --- a/drivers/gpu/drm/i915/i915_gem.c
> > +++ b/drivers/gpu/drm/i915/i915_gem.c
> > @@ -4687,14 +4687,16 @@ void __i915_gem_object_release_unless_active(struct drm_i915_gem_object *obj)
> >               i915_gem_object_put(obj);
> >  }
> >  
> > -static void assert_kernel_context_is_current(struct drm_i915_private *dev_priv)
> > +static void assert_kernel_context_is_current(struct drm_i915_private *i915)
> >  {
> > +     struct i915_gem_context *kernel_context = i915->kernel_context;
> >       struct intel_engine_cs *engine;
> >       enum intel_engine_id id;
> >  
> > -     for_each_engine(engine, dev_priv, id)
> > -             GEM_BUG_ON(engine->last_retired_context &&
> > -                        !i915_gem_context_is_kernel(engine->last_retired_context));
> > +     for_each_engine(engine, i915, id) {
> > +             GEM_BUG_ON(__i915_gem_active_peek(&engine->timeline->last_request));
> 
> It could be that we have a active request for kernel context and we
> still bail out with assert. Why?

Because we waited for the system to be idle, so we expect the timeline
to have been completely retired, which implies that
timline->last_request is now NULL.
-Chris