linux-kernel - Re: [PATCH v4 5/5] dma-buf/sync_file: only enable fence signalling on poll()

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Date:	Thu, 4 Aug 2016 18:18:53 -0300
From:	Gustavo Padovan <gustavo@...ovan.org>
To:	Chris Wilson <chris@...is-wilson.co.uk>,
	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,
	Gustavo Padovan <gustavo.padovan@...labora.co.uk>,
	John Harrison <John.C.Harrison@...el.com>, m.chehab@...sung.com
Subject: Re: [PATCH v4 5/5] dma-buf/sync_file: only enable fence signalling
 on poll()

2016-08-03 Chris Wilson <chris@...is-wilson.co.uk>:

> On Tue, Jul 12, 2016 at 03:08:45PM -0300, Gustavo Padovan wrote:
> > From: Gustavo Padovan <gustavo.padovan@...labora.co.uk>
> > 
> > Signalling doesn't need to be enabled at sync_file creation, it is only
> > required if userspace waiting the fence to signal through poll().
> > 
> > Thus we delay fence_add_callback() until poll is called. It only adds the
> > callback the first time poll() is called. This avoid re-adding the same
> > callback multiple times.
> > 
> > v2: rebase and update to work with new fence support for sync_file
> > 
> > v3: use atomic operation to set enabled and protect fence_add_callback()
> 
> There's actually a spare bit in fence->flags you can use for this.
> 
> #define POLL_ENABLED FENCE_FLAG_USER_BITS

Wouldn't it be better to add a new bit to fence_flags_bit?

	Gustavo