Re: [PATCH] drm/i915: Android sync points for i915

[Maarten Lankhorst <maarten.lankhorst@canonical.com>]

Hey,
On 31-07-14 20:58, Jesse Barnes wrote:
> Expose an ioctl to create Android fences based on the Android sync point
> infrastructure (which in turn is based on DMA-buf fences).  Just a
> sketch at this point, no testing has been done.
>
> There are a couple of goals here:
>   1) allow applications and libraries to create fences without an
>      associated buffer
>   2) re-use a common API so userspace doesn't have to impedance mismatch
>      between different driver implementations too much
>   3) allow applications and libraries to use explicit synchronization if
>      they choose by exposing fences directly
>
Do you really need to use android timelines here? I think you should be 
able to use fence directly, and export android userspace fences anyway, 
you could easily wrap them.

~Maarten

Untested uncompiled patch for that below, looking from the documentation I may have
caused a memory leak by taking a reference on the sync_pt..
---
diff --git a/drivers/staging/android/sync.c b/drivers/staging/android/sync.c
index ba0d69e..201b088 100644
--- a/drivers/staging/android/sync.c
+++ b/drivers/staging/android/sync.c
@@ -179,7 +179,7 @@ static void fence_check_cb_func(struct fence *f, struct fence_cb *cb)
 }
 
 /* TODO: implement a create which takes more that one sync_pt */
-struct sync_fence *sync_fence_create(const char *name, struct sync_pt *pt)
+struct sync_fence *sync_fence_create_dma(const char *name, struct fence *pt)
 {
 	struct sync_fence *fence;
 
@@ -190,16 +190,21 @@ struct sync_fence *sync_fence_create(const char *name, struct sync_pt *pt)
 	fence->num_fences = 1;
 	atomic_set(&fence->status, 1);
 
-	fence_get(&pt->base);
-	fence->cbs[0].sync_pt = &pt->base;
+	fence->cbs[0].sync_pt = fence_get(pt);
 	fence->cbs[0].fence = fence;
-	if (fence_add_callback(&pt->base, &fence->cbs[0].cb, fence_check_cb_func))
+	if (fence_add_callback(pt, &fence->cbs[0].cb, fence_check_cb_func))
 		atomic_dec(&fence->status);
 
 	sync_fence_debug_add(fence);
 
 	return fence;
 }
+EXPORT_SYMBOL(sync_fence_create_dma);
+
+struct sync_fence *sync_fence_create(const char *name, struct sync_pt *pt)
+{
+	return sync_fence_create_dma(name, &pt->base);
+}
 EXPORT_SYMBOL(sync_fence_create);
 
 struct sync_fence *sync_fence_fdget(int fd)
diff --git a/drivers/staging/android/sync.h b/drivers/staging/android/sync.h
index bcdd119..6d1682a 100644
--- a/drivers/staging/android/sync.h
+++ b/drivers/staging/android/sync.h
@@ -242,8 +242,9 @@ void sync_pt_free(struct sync_pt *pt);
  * @pt:		sync_pt to add to the fence
  *
  * Creates a fence containg @pt.  Once this is called, the fence takes
- * ownership of @pt.
+ * a reference on @pt.
  */
+struct sync_fence *sync_fence_create_dma(const char *name, struct fence *pt);
 struct sync_fence *sync_fence_create(const char *name, struct sync_pt *pt);
 
 /*