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, 12 insertions, 16 deletions

diff --git a/drivers/gpu/drm/i915/gt/intel_gt_pm.c b/drivers/gpu/drm/i915/gt/intel_gt_pm.c
index 6c8970271a7f..1363e069ec83 100644
--- a/drivers/gpu/drm/i915/gt/intel_gt_pm.c
+++ b/drivers/gpu/drm/i915/gt/intel_gt_pm.c
@@ -17,7 +17,7 @@ static void pm_notify(struct drm_i915_private *i915, int state)
 	blocking_notifier_call_chain(&i915->gt.pm_notifications, state, i915);
 }
 
-static int intel_gt_unpark(struct intel_wakeref *wf)
+static int __gt_unpark(struct intel_wakeref *wf)
 {
 	struct intel_gt *gt = container_of(wf, typeof(*gt), wakeref);
 	struct drm_i915_private *i915 = gt->i915;
@@ -53,14 +53,7 @@ static int intel_gt_unpark(struct intel_wakeref *wf)
 	return 0;
 }
 
-void intel_gt_pm_get(struct intel_gt *gt)
-{
-	struct intel_runtime_pm *rpm = &gt->i915->runtime_pm;
-
-	intel_wakeref_get(rpm, &gt->wakeref, intel_gt_unpark);
-}
-
-static int intel_gt_park(struct intel_wakeref *wf)
+static int __gt_park(struct intel_wakeref *wf)
 {
 	struct drm_i915_private *i915 =
 		container_of(wf, typeof(*i915), gt.wakeref);
@@ -74,22 +67,25 @@ static int intel_gt_park(struct intel_wakeref *wf)
 	if (INTEL_GEN(i915) >= 6)
 		gen6_rps_idle(i915);
 
+	/* Everything switched off, flush any residual interrupt just in case */
+	intel_synchronize_irq(i915);
+
 	GEM_BUG_ON(!wakeref);
 	intel_display_power_put(i915, POWER_DOMAIN_GT_IRQ, wakeref);
 
 	return 0;
 }
 
-void intel_gt_pm_put(struct intel_gt *gt)
-{
-	struct intel_runtime_pm *rpm = &gt->i915->runtime_pm;
-
-	intel_wakeref_put(rpm, &gt->wakeref, intel_gt_park);
-}
+static const struct intel_wakeref_ops wf_ops = {
+	.get = __gt_unpark,
+	.put = __gt_park,
+	.flags = INTEL_WAKEREF_PUT_ASYNC,
+};
 
 void intel_gt_pm_init_early(struct intel_gt *gt)
 {
-	intel_wakeref_init(&gt->wakeref);
+	intel_wakeref_init(&gt->wakeref, &gt->i915->runtime_pm, &wf_ops);
+
 	BLOCKING_INIT_NOTIFIER_HEAD(&gt->pm_notifications);
 }