Re: [PATCH 4/6] android: convert sync to fence api, v4

[Daniel Vetter <daniel@ffwll.ch>]

On Tue, Mar 04, 2014 at 08:50:38AM +0100, Maarten Lankhorst wrote:
> op 03-03-14 22:11, Daniel Vetter schreef:
> >On Mon, Feb 17, 2014 at 04:57:19PM +0100, Maarten Lankhorst wrote:
> >>Android syncpoints can be mapped to a timeline. This removes the need
> >>to maintain a separate api for synchronization. I've left the android
> >>trace events in place, but the core fence events should already be
> >>sufficient for debugging.
> >>
> >>v2:
> >>- Call fence_remove_callback in sync_fence_free if not all fences have fired.
> >>v3:
> >>- Merge Colin Cross' bugfixes, and the android fence merge optimization.
> >>v4:
> >>- Merge with the upstream fixes.
> >>
> >>Signed-off-by: Maarten Lankhorst <maarten.lankhorst@canonical.com>
> >>---
> >Snipped everything but headers - Ian Lister from our android team is
> >signed up to have a more in-depth look at proper integration with android
> >syncpoints. Adding him to cc.
> >
> >>diff --git a/drivers/staging/android/sync.h b/drivers/staging/android/sync.h
> >>index 62e2255b1c1e..6036dbdc8e6f 100644
> >>--- a/drivers/staging/android/sync.h
> >>+++ b/drivers/staging/android/sync.h
> >>@@ -21,6 +21,7 @@
> >>  #include <linux/list.h>
> >>  #include <linux/spinlock.h>
> >>  #include <linux/wait.h>
> >>+#include <linux/fence.h>
> >>
> >>  struct sync_timeline;
> >>  struct sync_pt;
> >>@@ -40,8 +41,6 @@ struct sync_fence;
> >>   * -1 if a will signal before b
> >>   * @free_pt: called before sync_pt is freed
> >>   * @release_obj: called before sync_timeline is freed
> >>- * @print_obj: deprecated
> >>- * @print_pt: deprecated
> >>   * @fill_driver_data: write implementation specific driver data to data.
> >>   *  should return an error if there is not enough room
> >>   *  as specified by size.  This information is returned
> >>@@ -67,13 +66,6 @@ struct sync_timeline_ops {
> >>   /* optional */
> >>   void (*release_obj)(struct sync_timeline *sync_timeline);
> >>
> >>- /* deprecated */
> >>- void (*print_obj)(struct seq_file *s,
> >>-  struct sync_timeline *sync_timeline);
> >>-
> >>- /* deprecated */
> >>- void (*print_pt)(struct seq_file *s, struct sync_pt *sync_pt);
> >>-
> >>   /* optional */
> >>   int (*fill_driver_data)(struct sync_pt *syncpt, void *data, int size);
> >>
> >>@@ -104,42 +96,48 @@ struct sync_timeline {
> >>
> >>   /* protected by child_list_lock */
> >>   bool destroyed;
> >>+ int context, value;
> >>
> >>   struct list_head child_list_head;
> >>   spinlock_t child_list_lock;
> >>
> >>   struct list_head active_list_head;
> >>- spinlock_t active_list_lock;
> >>
> >>+#ifdef CONFIG_DEBUG_FS
> >>   struct list_head sync_timeline_list;
> >>+#endif
> >>  };
> >>
> >>  /**
> >>   * struct sync_pt - sync point
> >>- * @parent: sync_timeline to which this sync_pt belongs
> >>+ * @fence: base fence class
> >>   * @child_list: membership in sync_timeline.child_list_head
> >>   * @active_list: membership in sync_timeline.active_list_head
> >>+<<<<<<< current
> >>   * @signaled_list: membership in temporary signaled_list on stack
> >>   * @fence: sync_fence to which the sync_pt belongs
> >>   * @pt_list: membership in sync_fence.pt_list_head
> >>   * @status: 1: signaled, 0:active, <0: error
> >>   * @timestamp: time which sync_pt status transitioned from active to
> >>   *  signaled or error.
> >>+=======
> >>+>>>>>>> patched
> >Conflict markers ...
> Oops.
> >>   */
> >>  struct sync_pt {
> >>- struct sync_timeline *parent;
> >>- struct list_head child_list;
> >>+ struct fence base;
> >Hm, embedding feels wrong, since that still means that I'll need to
> >implement two kinds of fences in i915 - one using the seqno fence to make
> >dma-buf sync work, and one to implmenent sync_pt to make the android folks
> >happy.
> >
> >If I can dream I think we should have a pointer to an underlying fence
> >here, i.e. a struct sync_pt would just be a userspace interface wrapper to
> >do explicit syncing using native fences, instead of implicit syncing like
> >with dma-bufs. But this is all drive-by comments from a very cursory
> >high-level look. I might be full of myself again ;-)
> >-Daniel
> >
> No, the idea is that because android syncpoint is simply another type of
> dma-fence, that if you deal with normal fences then android can
> automatically be handled too. The userspace fence api android exposes
> could be very easily made to work for dma-fence, just pass a dma-fence
> to sync_fence_create.
> So exposing dma-fence would probably work for android too.

Hm, then why do we still have struct sync_pt around? Since it's just the
internal bit, with the userspace facing object being struct sync_fence,
I'd opt to shuffle any useful features into the core struct fence.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch