drm/i915: Defer final intel_wakeref_put to process context

As we need to acquire a mutex to serialise the final
intel_wakeref_put, we need to ensure that we are in process context at
that time. However, we want to allow operation on the intel_wakeref from
inside timer and other hardirq context, which means that need to defer
that final put to a workqueue.

Inside the final wakeref puts, we are safe to operate in any context, as
we are simply marking up the HW and state tracking for the potential
sleep. It's only the serialisation with the potential sleeping getting
that requires careful wait avoidance. This allows us to retain the
immediate processing as before (we only need to sleep over the same
races as the current mutex_lock).

v2: Add a selftest to ensure we exercise the code while lockdep watches.
v3: That test was extremely loud and complained about many things!
v4: Not a whale!

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=111295
References: https://bugs.freedesktop.org/show_bug.cgi?id=111245
References: https://bugs.freedesktop.org/show_bug.cgi?id=111256
Fixes: 18398904ca9e ("drm/i915: Only recover active engines")
Fixes: 51fbd8de87dc ("drm/i915/pmu: Atomically acquire the gt_pm wakeref")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190808202758.10453-1-chris@chris-wilson.co.uk

1 files changed, 3 insertions, 10 deletions

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_pm.c b/drivers/gpu/drm/i915/gem/i915_gem_pm.c
index 72922703af49..17e3618241c5 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_pm.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_pm.c
@@ -130,7 +130,9 @@ static bool switch_to_kernel_context_sync(struct intel_gt *gt)
 		}
 	} while (i915_retire_requests(gt->i915) && result);
 
-	GEM_BUG_ON(gt->awake);
+	if (intel_gt_pm_wait_for_idle(gt))
+		result = false;
+
 	return result;
 }
 
@@ -161,13 +163,6 @@ void i915_gem_suspend(struct drm_i915_private *i915)
 
 	mutex_unlock(&i915->drm.struct_mutex);
 
-	/*
-	 * Assert that we successfully flushed all the work and
-	 * reset the GPU back to its idle, low power state.
-	 */
-	GEM_BUG_ON(i915->gt.awake);
-	flush_work(&i915->gem.idle_work);
-
 	cancel_delayed_work_sync(&i915->gt.hangcheck.work);
 
 	i915_gem_drain_freed_objects(i915);
@@ -244,8 +239,6 @@ void i915_gem_resume(struct drm_i915_private *i915)
 {
 	GEM_TRACE("\n");
 
-	WARN_ON(i915->gt.awake);
-
 	mutex_lock(&i915->drm.struct_mutex);
 	intel_uncore_forcewake_get(&i915->uncore, FORCEWAKE_ALL);