drm/i915: Provide an i915_active.acquire callback

If we introduce a callback for i915_active that is only called the first
time we use the i915_active and is symmetrically paired with the
i915_active.retire callback, we can replace the open-coded and
non-atomic implementations -- which will be very fragile (i.e. broken)
upon removing the struct_mutex serialisation.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190621183801.23252-4-chris@chris-wilson.co.uk

1 files changed, 8 insertions, 2 deletions

diff --git a/drivers/gpu/drm/i915/i915_active_types.h b/drivers/gpu/drm/i915/i915_active_types.h
index c025991b9233..5b0a3024ce24 100644
--- a/drivers/gpu/drm/i915/i915_active_types.h
+++ b/drivers/gpu/drm/i915/i915_active_types.h
@@ -7,7 +7,9 @@
 #ifndef _I915_ACTIVE_TYPES_H_
 #define _I915_ACTIVE_TYPES_H_
 
+#include <linux/atomic.h>
 #include <linux/llist.h>
+#include <linux/mutex.h>
 #include <linux/rbtree.h>
 #include <linux/rcupdate.h>
 
@@ -24,13 +26,17 @@ struct i915_active_request {
 	i915_active_retire_fn retire;
 };
 
+struct active_node;
+
 struct i915_active {
 	struct drm_i915_private *i915;
 
+	struct active_node *cache;
 	struct rb_root tree;
-	struct i915_active_request last;
-	unsigned int count;
+	struct mutex mutex;
+	atomic_t count;
 
+	int (*active)(struct i915_active *ref);
 	void (*retire)(struct i915_active *ref);
 
 	struct llist_head barriers;