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, 42 insertions, 20 deletions

diff --git a/drivers/gpu/drm/i915/intel_wakeref.h b/drivers/gpu/drm/i915/intel_wakeref.h
index 1d6f5986e4e5..535a3a12864b 100644
--- a/drivers/gpu/drm/i915/intel_wakeref.h
+++ b/drivers/gpu/drm/i915/intel_wakeref.h
@@ -8,10 +8,12 @@
 #define INTEL_WAKEREF_H
 
 #include <linux/atomic.h>
+#include <linux/bits.h>
 #include <linux/mutex.h>
 #include <linux/refcount.h>
 #include <linux/stackdepot.h>
 #include <linux/timer.h>
+#include <linux/workqueue.h>
 
 #if IS_ENABLED(CONFIG_DRM_I915_DEBUG)
 #define INTEL_WAKEREF_BUG_ON(expr) BUG_ON(expr)
@@ -20,29 +22,42 @@
 #endif
 
 struct intel_runtime_pm;
+struct intel_wakeref;
 
 typedef depot_stack_handle_t intel_wakeref_t;
 
+struct intel_wakeref_ops {
+	int (*get)(struct intel_wakeref *wf);
+	int (*put)(struct intel_wakeref *wf);
+
+	unsigned long flags;
+#define INTEL_WAKEREF_PUT_ASYNC BIT(0)
+};
+
 struct intel_wakeref {
 	atomic_t count;
 	struct mutex mutex;
+
 	intel_wakeref_t wakeref;
+
+	struct intel_runtime_pm *rpm;
+	const struct intel_wakeref_ops *ops;
+
+	struct work_struct work;
 };
 
 void __intel_wakeref_init(struct intel_wakeref *wf,
+			  struct intel_runtime_pm *rpm,
+			  const struct intel_wakeref_ops *ops,
 			  struct lock_class_key *key);
-#define intel_wakeref_init(wf) do {					\
+#define intel_wakeref_init(wf, rpm, ops) do {				\
 	static struct lock_class_key __key;				\
 									\
-	__intel_wakeref_init((wf), &__key);				\
+	__intel_wakeref_init((wf), (rpm), (ops), &__key);		\
 } while (0)
 
-int __intel_wakeref_get_first(struct intel_runtime_pm *rpm,
-			      struct intel_wakeref *wf,
-			      int (*fn)(struct intel_wakeref *wf));
-int __intel_wakeref_put_last(struct intel_runtime_pm *rpm,
-			     struct intel_wakeref *wf,
-			     int (*fn)(struct intel_wakeref *wf));
+int __intel_wakeref_get_first(struct intel_wakeref *wf);
+void __intel_wakeref_put_last(struct intel_wakeref *wf);
 
 /**
  * intel_wakeref_get: Acquire the wakeref
@@ -61,12 +76,10 @@ int __intel_wakeref_put_last(struct intel_runtime_pm *rpm,
  * code otherwise.
  */
 static inline int
-intel_wakeref_get(struct intel_runtime_pm *rpm,
-		  struct intel_wakeref *wf,
-		  int (*fn)(struct intel_wakeref *wf))
+intel_wakeref_get(struct intel_wakeref *wf)
 {
 	if (unlikely(!atomic_inc_not_zero(&wf->count)))
-		return __intel_wakeref_get_first(rpm, wf, fn);
+		return __intel_wakeref_get_first(wf);
 
 	return 0;
 }
@@ -102,16 +115,12 @@ intel_wakeref_get_if_active(struct intel_wakeref *wf)
  * Returns: 0 if the wakeref was released successfully, or a negative error
  * code otherwise.
  */
-static inline int
-intel_wakeref_put(struct intel_runtime_pm *rpm,
-		  struct intel_wakeref *wf,
-		  int (*fn)(struct intel_wakeref *wf))
+static inline void
+intel_wakeref_put(struct intel_wakeref *wf)
 {
 	INTEL_WAKEREF_BUG_ON(atomic_read(&wf->count) <= 0);
-	if (atomic_dec_and_mutex_lock(&wf->count, &wf->mutex))
-		return __intel_wakeref_put_last(rpm, wf, fn);
-
-	return 0;
+	if (unlikely(!atomic_add_unless(&wf->count, -1, 1)))
+		__intel_wakeref_put_last(wf);
 }
 
 /**
@@ -154,6 +163,19 @@ intel_wakeref_is_active(const struct intel_wakeref *wf)
 	return READ_ONCE(wf->wakeref);
 }
 
+/**
+ * intel_wakeref_wait_for_idle: Wait until the wakeref is idle
+ * @wf: the wakeref
+ *
+ * Wait for the earlier asynchronous release of the wakeref. Note
+ * this will wait for any third party as well, so make sure you only wait
+ * when you have control over the wakeref and trust no one else is acquiring
+ * it.
+ *
+ * Return: 0 on success, error code if killed.
+ */
+int intel_wakeref_wait_for_idle(struct intel_wakeref *wf);
+
 struct intel_wakeref_auto {
 	struct intel_runtime_pm *rpm;
 	struct timer_list timer;