linux-kernel - Re: [PATCH 1/2] dma-buf/fence: add fence

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Date:	Thu, 19 May 2016 09:57:27 +0200
From:	Daniel Vetter <daniel@...ll.ch>
To:	Christian König <christian.koenig@....com>
Cc:	Chris Wilson <chris@...is-wilson.co.uk>,
	Gustavo Padovan <gustavo@...ovan.org>,
	dri-devel@...ts.freedesktop.org, marcheu@...gle.com,
	Daniel Stone <daniels@...labora.com>, seanpaul@...gle.com,
	Daniel Vetter <daniel.vetter@...ll.ch>,
	linux-kernel@...r.kernel.org, laurent.pinchart@...asonboard.com,
	Alex Deucher <alexander.deucher@....com>,
	Gustavo Padovan <gustavo.padovan@...labora.co.uk>,
	John Harrison <John.C.Harrison@...el.com>, m.chehab@...sung.com
Subject: Re: [PATCH 1/2] dma-buf/fence: add fence_collection fences

On Thu, May 19, 2016 at 09:46:47AM +0200, Christian König wrote:
> Am 19.05.2016 um 00:57 schrieb Chris Wilson:
> >On Wed, May 18, 2016 at 05:59:52PM -0300, Gustavo Padovan wrote:
> >>+static void collection_check_cb_func(struct fence *fence, struct fence_cb *cb)
> >>+{
> >>+	struct fence_collection_cb *f_cb;
> >>+	struct fence_collection *collection;
> >>+
> >>+	f_cb = container_of(cb, struct fence_collection_cb, cb);
> >>+	collection = f_cb->collection;
> >>+
> >>+	if (atomic_dec_and_test(&collection->num_pending_fences))
> >>+		fence_signal(&collection->base);
> >>+}
> >>+
> >>+static bool fence_collection_enable_signaling(struct fence *fence)
> >>+{
> >>+	struct fence_collection *collection = to_fence_collection(fence);
> >>+	int i;
> >>+
> >>+	for (i = 0 ; i < collection->num_fences ; i++) {
> >>+		if (fence_add_callback(collection->fences[i].fence,
> >>+				       &collection->fences[i].cb,
> >>+				       collection_check_cb_func)) {
> >>+			atomic_dec(&collection->num_pending_fences);
> >>+		}
> >>+	}
> >We don't always have a convenient means to preallocate an array of
> >fences to use. Keeping a list of fences in addition to the array would
> >be easier to user in many circumstances.
> 
> I agree that there is use for such an implementation as well, but as
> mentioned in the last review cycle we intentionally chose an array instead
> of a more complex implementation here.
> 
> This way the array can be passed to function like fence_wait_any_timeout()
> as well.

+1 on fence_array.

> I also suggested to rename it to fence_array to make that difference clear
> and allow for another implementation to live side by side with this.
> 
> My crux at the moment is that I need both for the amdgpu driver, an array
> based implementation and a collection like one.
> 
> Gustavo would you mind if I take your patches and work a bit on this?

I think the goal is to start landing the atomic fence stuff in 4.8.
Probably simplest if we converge on a first iteration that I can pull into
drm-misc right after 4.7-rc1. Then you can both base your respective work
on top of that branch (it's a stable one, so can even base official
branches on it).
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch