[PATCH 2/7] drm/i915: Only sync tasklets once for recursive reset preparation

[Chris Wilson]

When setting up reset, we may need to recursively prepare an engine. In
which case we should only synchronously flush the tasklets on the outer
most call, the inner calls will then be inside an atomic section where
the tasklet will never be run (and so the sync will never complete).

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/i915_gem.c     |  2 +-
 drivers/gpu/drm/i915/i915_gem.h     |  7 +++
 drivers/gpu/drm/i915/i915_tasklet.h | 84 +++++++++++++++++++++++++++++
 3 files changed, 92 insertions(+), 1 deletion(-)
 create mode 100644 drivers/gpu/drm/i915/i915_tasklet.h

diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 0dc369a9ec4d..aab1f5e77ae9 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -3036,7 +3036,7 @@ i915_gem_reset_prepare_engine(struct intel_engine_cs *engine)
 	 * Turning off the execlists->tasklet until the reset is over
 	 * prevents the race.
 	 */
-	tasklet_disable(&engine->execlists.tasklet);
+	__tasklet_disable_once(&engine->execlists.tasklet);
 
 	/*
 	 * We're using worker to queue preemption requests from the tasklet in
diff --git a/drivers/gpu/drm/i915/i915_gem.h b/drivers/gpu/drm/i915/i915_gem.h
index 525920404ede..af033e7c1c56 100644
--- a/drivers/gpu/drm/i915/i915_gem.h
+++ b/drivers/gpu/drm/i915/i915_gem.h
@@ -26,6 +26,7 @@
 #define __I915_GEM_H__
 
 #include <linux/bug.h>
+#include <linux/interrupt.h>
 
 struct drm_i915_private;
 
@@ -72,4 +73,10 @@ struct drm_i915_private;
 void i915_gem_park(struct drm_i915_private *i915);
 void i915_gem_unpark(struct drm_i915_private *i915);
 
+static inline void __tasklet_disable_once(struct tasklet_struct *t)
+{
+	if (atomic_inc_return(&t->count) == 1)
+		tasklet_unlock_wait(t);
+}
+
 #endif /* __I915_GEM_H__ */
diff --git a/drivers/gpu/drm/i915/i915_tasklet.h b/drivers/gpu/drm/i915/i915_tasklet.h
new file mode 100644
index 000000000000..b7cbbc2f8f69
--- /dev/null
+++ b/drivers/gpu/drm/i915/i915_tasklet.h
@@ -0,0 +1,84 @@
+/*
+ * SPDX-License-Identifier: GPL-2.0
+ *
+ * Copyright © 2018 Intel Corporation
+ */
+
+#ifndef _I915_TASKLET_H_
+#define _I915_TASKLET_H_
+
+#include <linux/atomic.h>
+#include <linux/interrupt.h>
+
+/**
+ * struct i915_tasklet - wrapper around tasklet_struct
+ *
+ * We want to abuse tasklets slightly, such as calling them directly. In some
+ * cases, this requires some auxiliary tracking so subclass the tasklet_struct
+ * so that we have a central place and helpers.
+ */
+struct i915_tasklet {
+	struct tasklet_struct base;
+};
+
+static inline void i915_tasklet_init(struct i915_tasklet *t,
+				     void (*func)(unsigned long),
+				     unsigned long data)
+{
+	tasklet_init(&t->base, func, data);
+}
+
+static inline bool i915_tasklet_is_scheduled(const struct i915_tasklet *t)
+{
+	return test_bit(TASKLET_STATE_SCHED, &t->base.state);
+}
+
+static inline bool i915_tasklet_is_running(const struct i915_tasklet *t)
+{
+	return test_bit(TASKLET_STATE_RUN, &t->base.state);
+}
+
+static inline bool i915_tasklet_is_enabled(const struct i915_tasklet *t)
+{
+	return likely(!atomic_read(&t->base.count));
+}
+
+static inline void i915_tasklet_schedule(struct i915_tasklet *t)
+{
+	tasklet_hi_schedule(&t->base);
+}
+
+static inline void i915_tasklet_flush(struct i915_tasklet *t)
+{
+	tasklet_kill(&t->base);
+}
+
+static inline void i915_tasklet_disable(struct i915_tasklet *t)
+{
+	tasklet_disable(&t->base);
+}
+
+static inline void i915_tasklet_disable_once(struct i915_tasklet *t)
+{
+	if (atomic_inc_return(&t->base.count) == 1)
+		tasklet_unlock_wait(&t->base);
+}
+
+static inline void i915_tasklet_enable(struct i915_tasklet *t)
+{
+	tasklet_enable(&t->base);
+}
+
+static inline void i915_tasklet_set_func(struct i915_tasklet *t,
+					 void (*func)(unsigned long data),
+					 unsigned long data)
+{
+	i915_tasklet_disable(t);
+
+	t->base.func = func;
+	t->base.data = data;
+
+	i915_tasklet_enable(t);
+}
+
+#endif /* _I915_TASKLET_H_ */
-- 
2.17.0