Message-ID: <53158CEA.30004@canonical.com>
Date:	Tue, 04 Mar 2014 09:20:58 +0100
From:	Maarten Lankhorst <maarten.lankhorst@...onical.com>
To:	Ian Lister <ian.lister@...el.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-arch@...r.kernel.org, Colin Cross <ccross@...gle.com>,
	"linaro-mm-sig@...ts.linaro.org" <linaro-mm-sig@...ts.linaro.org>,
	"Clark, Rob" <robdclark@...il.com>,
	dri-devel <dri-devel@...ts.freedesktop.org>,
	Sumit Semwal <sumit.semwal@...aro.org>,
	"linux-media@...r.kernel.org" <linux-media@...r.kernel.org>
Subject: Re: [PATCH 4/6] android: convert sync to fence api, v4

op 04-03-14 09:14, Daniel Vetter schreef:
> 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@...onical.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
To keep compatibility with the android api. I think that gradually converting them is going to be
more useful than to force all drivers to use a new api all at once. They could keep android
syncpoint api for exporting, as long as they accept dma-fence for importing/waiting.

~Maarten
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