linux-kernel - Re: [RFC][PATCH 0/2] dma-buf: add importer private data for reimporting

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Message-ID: <1370017269.4135.2.camel@weser.hi.pengutronix.de>
Date:	Fri, 31 May 2013 18:21:09 +0200
From:	Lucas Stach <l.stach@...gutronix.de>
To:	Daniel Vetter <daniel@...ll.ch>
Cc:	김승우 <sw0312.kim@...sung.com>,
	Daniel Vetter <daniel.vetter@...ll.ch>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	dri-devel <dri-devel@...ts.freedesktop.org>,
	"linaro-mm-sig@...ts.linaro.org" <linaro-mm-sig@...ts.linaro.org>,
	Kyungmin Park <kyungmin.park@...sung.com>,
	"linux-media@...r.kernel.org" <linux-media@...r.kernel.org>
Subject: Re: [RFC][PATCH 0/2] dma-buf: add importer private data for
 reimporting

Am Freitag, den 31.05.2013, 17:29 +0200 schrieb Daniel Vetter:
> On Fri, May 31, 2013 at 07:22:24PM +0900, 김승우 wrote:
> > Hello Daniel,
> > 
> > Thanks for your comment.
> > 
> > On 2013년 05월 31일 18:14, Daniel Vetter wrote:
> > > On Fri, May 31, 2013 at 10:54 AM, Seung-Woo Kim <sw0312.kim@...sung.com> wrote:
> > >> importer private data in dma-buf attachment can be used by importer to
> > >> reimport same dma-buf.
> > >>
> > >> Seung-Woo Kim (2):
> > >>   dma-buf: add importer private data to attachment
> > >>   drm/prime: find gem object from the reimported dma-buf
> > > 
> > > Self-import should already work (at least with the latest refcount
> > > fixes merged). At least the tests to check both re-import on the same
> > > drm fd and on a different all work as expected now.
> > 
> > Currently, prime works well for all case including self-importing,
> > importing, and reimporting as you describe. Just, importing dma-buf from
> > other driver twice with different drm_fd, each import create its own gem
> > object even two import is done for same buffer because prime_priv is in
> > struct drm_file. This means mapping to the device is done also twice.
> > IMHO, these duplicated creations and maps are not necessary if drm can
> > find previous import in different prime_priv.
> 
> Well, that's imo a bug with the other driver. If it doesn't export
> something really simple (e.g. contiguous memory which doesn't require any
> mmio resources at all) it should have a cache of exported dma_buf fds so
> that it hands out the same dma_buf every time.

I agree with the reasoning here.

Though it would be nice to have this "expected driver behavior" put down
somewhere in the documentation. Any volunteers?

Regards,
Lucas
-- 
Pengutronix e.K.                           | Lucas Stach                 |
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