drm/i915/gt: Assert the kernel context is using the HWSP

We need to ensure that the kernel context is using the permanently pinned
HWSP so that we can always submit a pm request from any context. By
construction, the engine->kernel_context should only be using the
engine->status_page.vma so let's assert that is still true when we have
to submit a request for parking the engine.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200714114419.28713-1-chris@chris-wilson.co.uk

Author: ickle

drivers/gpu/drm/i915/gt/intel_engine_pm.c

@@ -142,6 +142,7 @@ static bool switch_to_kernel_context(struct intel_engine_cs *engine)
 		return true;
 
 	GEM_BUG_ON(!intel_context_is_barrier(ce));
+	GEM_BUG_ON(ce->timeline->hwsp_ggtt != engine->status_page.vma);
 
 	/* Already inside the kernel context, safe to power down. */
 	if (engine->wakeref_serial == engine->serial)