linux-kernel - Re: [RFC v2 5/8] drm/fence: add in-fences support

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Message-ID: <CAKMK7uGArBc37zOwsTXDEJrN+OdXXWnjSUWiKVDCmLAY4uDGYQ@mail.gmail.com>
Date:	Thu, 28 Apr 2016 22:40:10 +0200
From:	Daniel Vetter <daniel@...ll.ch>
To:	Ville Syrjälä <ville.syrjala@...ux.intel.com>
Cc:	Gustavo Padovan <gustavo@...ovan.org>,
	Daniel Stone <daniel@...ishbar.org>,
	Greg Hackmann <ghackmann@...gle.com>,
	Gustavo Padovan <gustavo.padovan@...labora.co.uk>,
	Daniel Stone <daniels@...labora.com>,
	Riley Andrews <riandrews@...roid.com>,
	dri-devel <dri-devel@...ts.freedesktop.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Arve Hjønnevåg <arve@...roid.com>,
	John Harrison <John.C.Harrison@...el.com>
Subject: Re: [RFC v2 5/8] drm/fence: add in-fences support

On Thu, Apr 28, 2016 at 8:17 PM, Ville Syrjälä
<ville.syrjala@...ux.intel.com> wrote:
>> >  - implicit fences also needs one fence per plane/fb, so it will be good to
>> >    match with that.
>>
>> We would actually need a fence per object rather than per fb.
>
> I guess you could overcome this by automagically creating a merged fence
> for a multi-obj fb?

Yeah, and the android hwc does this for you already. You get passed a
surface (or whatever it's called exactly) plus a fence, and the
surface contains the gralloc/native buffer thing, which would contain
multiple dma-buf handles if your hw does planar stuff that way.

I think everyone else who wants explicit fencing will go with the same
or similar model, so it's just about implicit fencing. And there we
can easily construct the fence_collection from a drm_framebuffer
ourselves with a small helper in each driver (or shared one in cma,
although cma doesn't yet grok reserverations/implicitly attached
fences).
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch