linux-kernel - Re: [RFC 0/6] drm/fences: add in-fences to DRM

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Message-ID: <CAPj87rP38wGwbZkEveY3QL+99_PesKfMMRy2bDnOhrmPPQ7RmQ@mail.gmail.com>
Date:	Thu, 31 Mar 2016 12:41:09 +0100
From:	Daniel Stone <daniel@...ishbar.org>
To:	Inki Dae <daeinki@...il.com>
Cc:	Daniel Vetter <daniel.vetter@...ll.ch>,
	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Riley Andrews <riandrews@...roid.com>,
	Arve Hjønnevåg <arve@...roid.com>,
	Gustavo Padovan <gustavo.padovan@...labora.co.uk>,
	John Harrison <John.C.Harrison@...el.com>
Subject: Re: [RFC 0/6] drm/fences: add in-fences to DRM

Hi Inki,

On 31 March 2016 at 12:26, Inki Dae <daeinki@...il.com> wrote:
> 2016-03-31 19:56 GMT+09:00 Daniel Stone <daniel@...ishbar.org>:
>> On 31 March 2016 at 11:05, Inki Dae <inki.dae@...sung.com> wrote:
>>> Then, existing drivers would need additional works for explicit fencing support. This wouldn't be really what the drivers have to but should be handled with this patch series because this would affect exising device drivers which use implicit fencing.
>>
>> Well, yes. Anyone implementing their own atomic commit would need to
>> ensure that the commit works properly for fences. The helpers could
>> also add it, but the helpers are not mandatory, and you are not
>> required to use every part of the helper to use one part of the
>> helper. There is no magic wand you can wave that instantly makes it
>> work for every driver
>
> I meant there are already several DRM drivers which work properly for
> implicit fence. So if atomic helper framework of DRM core is
> considered only for the explicit fence, then fencing operation would
> affect the existing DRM drivers. So I hope this trying could consider
> existing implicit fence users.

Yes, absolutely. Implicit fencing is already part of userspace ABI
that we can effectively never remove: it would break everyone's
desktops on Intel alone, as well as many others. So explicit will be
opt-in from the user and the driver both, and only when the
combination is fully supported will explicit fencing be used.

Cheers,
Daniel