linux-kernel - Re: [PATCH 09/17] drm/radeon: use common fence implementation for fences

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Date:	Tue, 22 Jul 2014 17:19:56 +0200
From:	Daniel Vetter <daniel@...ll.ch>
To:	Christian König <christian.koenig@....com>
Cc:	Maarten Lankhorst <maarten.lankhorst@...onical.com>,
	Christian König <deathsimple@...afone.de>,
	Dave Airlie <airlied@...il.com>,
	Thomas Hellstrom <thellstrom@...are.com>,
	nouveau <nouveau@...ts.freedesktop.org>,
	LKML <linux-kernel@...r.kernel.org>,
	dri-devel <dri-devel@...ts.freedesktop.org>,
	Ben Skeggs <bskeggs@...hat.com>,
	"Deucher, Alexander" <alexander.deucher@....com>
Subject: Re: [PATCH 09/17] drm/radeon: use common fence implementation for fences

On Tue, Jul 22, 2014 at 4:39 PM, Christian König
<christian.koenig@....com> wrote:
> Am 22.07.2014 16:27, schrieb Maarten Lankhorst:
>
>> op 22-07-14 16:24, Christian König schreef:
>>>>
>>>> No, you really shouldn't be doing much in the check anyway, it's meant
>>>> to be a lightweight check. If you're not ready yet because of a lockup
>>>> simply return not signaled yet.
>>>
>>> It's not only the lockup case from radeon I have in mind here. For
>>> userspace queues it might be necessary to call copy_from_user to figure out
>>> if a fence is signaled or not.
>>>
>>> Returning false all the time is probably not a good idea either.
>>
>> Having userspace implement a fence sounds like an awful idea, why would
>> you want to do that?
>
>
> Marketing moves in mysterious ways. Don't ask me, but that the direction it
> currently moves with userspace queues and IOMMU etc...

Fence-based syncing between userspace queues submitted stuff through
doorbells and anything submitted by the general simply wont work.
Which is why I think the doorbell is a stupid interface since I just
don't see cameras and v4l devices implementing all that complexity to
get a pure userspace side sync solution.

But that's a different problem really, and I guess marketing will
eventually figure this one out, too.
-Daniel

-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch
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