Re: [Intel-gfx] [PATCH v4 2/4] drm/i915: Add getter/setter for i915_gem_object->frontbuffer

[Nirmoy Das]

On 7/27/2023 8:41 AM, Jouni Högander wrote:

Add getter/setter for i915_gem_object->frontbuffer and use it instead of
directly touching i915_gem_object->frontbuffer frontbuffer pointer.

v3:
  - Fix intel_frontbuffer_get return value
  - s/front_ret/cur/
v2: Move getter/setter into i915_gem_object.h

Signed-off-by: Jouni Högander <jouni.hogan...@intel.com>

Reviewed-by: Nirmoy Das <nirmoy....@intel.com>

---
  .../gpu/drm/i915/display/intel_frontbuffer.c  | 20 ++----
  .../gpu/drm/i915/display/intel_frontbuffer.h  | 27 --------
  drivers/gpu/drm/i915/gem/i915_gem_object.c    |  4 +-
  drivers/gpu/drm/i915/gem/i915_gem_object.h    | 67 +++++++++++++++++++
  drivers/gpu/drm/i915/i915_vma.c               |  2 +-
  5 files changed, 77 insertions(+), 43 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/intel_frontbuffer.c 
b/drivers/gpu/drm/i915/display/intel_frontbuffer.c
index 3ce0436a0c7d..56f45370fee0 100644
--- a/drivers/gpu/drm/i915/display/intel_frontbuffer.c
+++ b/drivers/gpu/drm/i915/display/intel_frontbuffer.c
@@ -237,7 +237,7 @@ static void frontbuffer_release(struct kref *ref)
        }
        spin_unlock(&obj->vma.lock);

- RCU_INIT_POINTER(obj->frontbuffer, NULL);

+       i915_gem_object_set_frontbuffer(obj, NULL);
        spin_unlock(&intel_bo_to_i915(obj)->display.fb_tracking.lock);

i915_active_fini(&front->write);

@@ -250,9 +250,9 @@ struct intel_frontbuffer *
  intel_frontbuffer_get(struct drm_i915_gem_object *obj)
  {
        struct drm_i915_private *i915 = intel_bo_to_i915(obj);
-       struct intel_frontbuffer *front;
+       struct intel_frontbuffer *front, *cur;

- front = __intel_frontbuffer_get(obj);

+       front = i915_gem_object_get_frontbuffer(obj);
        if (front)
                return front;

@@ -269,17 +269,11 @@ intel_frontbuffer_get(struct drm_i915_gem_object *obj)

                         I915_ACTIVE_RETIRE_SLEEPS);

spin_lock(&i915->display.fb_tracking.lock);

-       if (rcu_access_pointer(obj->frontbuffer)) {
-               kfree(front);
-               front = rcu_dereference_protected(obj->frontbuffer, true);
-               kref_get(&front->ref);
-       } else {
-               i915_gem_object_get(obj);
-               rcu_assign_pointer(obj->frontbuffer, front);
-       }
+       cur = i915_gem_object_set_frontbuffer(obj, front);
        spin_unlock(&i915->display.fb_tracking.lock);
-
-       return front;
+       if (cur != front)
+               kfree(front);
+       return cur;
  }

void intel_frontbuffer_put(struct intel_frontbuffer *front)

diff --git a/drivers/gpu/drm/i915/display/intel_frontbuffer.h 
b/drivers/gpu/drm/i915/display/intel_frontbuffer.h
index 3c474ed937fb..eeccc847331d 100644
--- a/drivers/gpu/drm/i915/display/intel_frontbuffer.h
+++ b/drivers/gpu/drm/i915/display/intel_frontbuffer.h
@@ -75,33 +75,6 @@ void intel_frontbuffer_flip(struct drm_i915_private *i915,

void intel_frontbuffer_put(struct intel_frontbuffer *front); -static inline struct intel_frontbuffer *

-__intel_frontbuffer_get(const struct drm_i915_gem_object *obj)
-{
-       struct intel_frontbuffer *front;
-
-       if (likely(!rcu_access_pointer(obj->frontbuffer)))
-               return NULL;
-
-       rcu_read_lock();
-       do {
-               front = rcu_dereference(obj->frontbuffer);
-               if (!front)
-                       break;
-
-               if (unlikely(!kref_get_unless_zero(&front->ref)))
-                       continue;
-
-               if (likely(front == rcu_access_pointer(obj->frontbuffer)))
-                       break;
-
-               intel_frontbuffer_put(front);
-       } while (1);
-       rcu_read_unlock();
-
-       return front;
-}
-
  struct intel_frontbuffer *
  intel_frontbuffer_get(struct drm_i915_gem_object *obj);

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_object.c b/drivers/gpu/drm/i915/gem/i915_gem_object.c

index 97ac6fb37958..148468098082 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_object.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_object.c
@@ -469,7 +469,7 @@ void __i915_gem_object_flush_frontbuffer(struct 
drm_i915_gem_object *obj,
  {
        struct intel_frontbuffer *front;

- front = __intel_frontbuffer_get(obj);

+       front = i915_gem_object_get_frontbuffer(obj);
        if (front) {
                intel_frontbuffer_flush(front, origin);
                intel_frontbuffer_put(front);
@@ -481,7 +481,7 @@ void __i915_gem_object_invalidate_frontbuffer(struct 
drm_i915_gem_object *obj,
  {
        struct intel_frontbuffer *front;

- front = __intel_frontbuffer_get(obj);

+       front = i915_gem_object_get_frontbuffer(obj);
        if (front) {
                intel_frontbuffer_invalidate(front, origin);
                intel_frontbuffer_put(front);
diff --git a/drivers/gpu/drm/i915/gem/i915_gem_object.h 
b/drivers/gpu/drm/i915/gem/i915_gem_object.h
index 884a17275b3a..112c130cfaaa 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_object.h
+++ b/drivers/gpu/drm/i915/gem/i915_gem_object.h
@@ -891,4 +891,71 @@ static inline int i915_gem_object_userptr_validate(struct 
drm_i915_gem_object *o

#endif +/**

+ * i915_gem_object_get_frontbuffer - Get the object's frontbuffer
+ * @obj: The object whose frontbuffer to get.
+ *
+ * Get pointer to object's frontbuffer if such exists. Please note that RCU
+ * mechanism is used to handle e.g. ongoing removal of frontbuffer pointer.
+ *
+ * Return: pointer to object's frontbuffer is such exists or NULL
+ */
+static inline struct intel_frontbuffer *
+i915_gem_object_get_frontbuffer(const struct drm_i915_gem_object *obj)
+{
+       struct intel_frontbuffer *front;
+
+       if (likely(!rcu_access_pointer(obj->frontbuffer)))
+               return NULL;
+
+       rcu_read_lock();
+       do {
+               front = rcu_dereference(obj->frontbuffer);
+               if (!front)
+                       break;
+
+               if (unlikely(!kref_get_unless_zero(&front->ref)))
+                       continue;
+
+               if (likely(front == rcu_access_pointer(obj->frontbuffer)))
+                       break;
+
+               intel_frontbuffer_put(front);
+       } while (1);
+       rcu_read_unlock();
+
+       return front;
+}
+
+/**
+ * i915_gem_object_set_frontbuffer - Set the object's frontbuffer
+ * @obj: The object whose frontbuffer to set.
+ * @front: The frontbuffer to set
+ *
+ * Set object's frontbuffer pointer. If frontbuffer is already set for the
+ * object keep it and return it's pointer to the caller. Please note that RCU
+ * mechanism is used to handle e.g. ongoing removal of frontbuffer pointer. 
This
+ * function is protected by i915->display.fb_tracking.lock
+ *
+ * Return: pointer to frontbuffer which was set.
+ */
+static inline struct intel_frontbuffer *
+i915_gem_object_set_frontbuffer(struct drm_i915_gem_object *obj,
+                               struct intel_frontbuffer *front)
+{
+       struct intel_frontbuffer *cur = front;
+
+       if (!front) {
+               RCU_INIT_POINTER(obj->frontbuffer, NULL);
+       } else if (rcu_access_pointer(obj->frontbuffer)) {
+               cur = rcu_dereference_protected(obj->frontbuffer, true);
+               kref_get(&cur->ref);
+       } else {
+               drm_gem_object_get(intel_bo_to_drm_bo(obj));
+               rcu_assign_pointer(obj->frontbuffer, front);
+       }
+
+       return cur;
+}
+
  #endif
diff --git a/drivers/gpu/drm/i915/i915_vma.c b/drivers/gpu/drm/i915/i915_vma.c
index af2e49f90f2f..e90b9c812180 100644
--- a/drivers/gpu/drm/i915/i915_vma.c
+++ b/drivers/gpu/drm/i915/i915_vma.c
@@ -1908,7 +1908,7 @@ int _i915_vma_move_to_active(struct i915_vma *vma,
        if (flags & EXEC_OBJECT_WRITE) {
                struct intel_frontbuffer *front;

- front = __intel_frontbuffer_get(obj);

+               front = i915_gem_object_get_frontbuffer(obj);
                if (unlikely(front)) {
                        if (intel_frontbuffer_invalidate(front, ORIGIN_CS))
                                i915_active_add_request(&front->write, rq);