linux-kernel - Re: [PATCH v5 5/8] iio: core: Add new DMABUF interface infrastructure

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Message-ID: <f676839ba47eefe7c33d3f46f4517fbdb1d01c7a.camel@crapouillou.net>
Date: Mon, 29 Jan 2024 15:15:08 +0100
From: Paul Cercueil <paul@...pouillou.net>
To: Christian König <christian.koenig@....com>, 
	Jonathan Cameron
	 <jic23@...nel.org>
Cc: Lars-Peter Clausen <lars@...afoo.de>, Sumit Semwal
 <sumit.semwal@...aro.org>,  Vinod Koul <vkoul@...nel.org>, Jonathan Corbet
 <corbet@....net>, linux-doc@...r.kernel.org,  linux-kernel@...r.kernel.org,
 dmaengine@...r.kernel.org,  linux-iio@...r.kernel.org,
 linux-media@...r.kernel.org,  dri-devel@...ts.freedesktop.org,
 linaro-mm-sig@...ts.linaro.org, Nuno Sá
 <noname.nuno@...il.com>, Michael Hennerich <Michael.Hennerich@...log.com>
Subject: Re: [PATCH v5 5/8] iio: core: Add new DMABUF interface
 infrastructure

Le lundi 29 janvier 2024 à 14:32 +0100, Paul Cercueil a écrit :
> Le lundi 29 janvier 2024 à 14:17 +0100, Christian König a écrit :
> > Am 29.01.24 um 14:06 schrieb Paul Cercueil:
> > > Hi Christian,
> > > 
> > > Le lundi 29 janvier 2024 à 13:52 +0100, Christian König a écrit :
> > > > Am 27.01.24 um 17:50 schrieb Jonathan Cameron:
> > > > > > > > +	iio_buffer_dmabuf_put(attach);
> > > > > > > > +
> > > > > > > > +out_dmabuf_put:
> > > > > > > > +	dma_buf_put(dmabuf);
> > > > > > > As below. Feels like a __free(dma_buf_put) bit of magic
> > > > > > > would
> > > > > > > be a
> > > > > > > nice to have.
> > > > > > I'm working on the patches right now, just one quick
> > > > > > question.
> > > > > > 
> > > > > > Having a __free(dma_buf_put) requires that dma_buf_put is
> > > > > > first
> > > > > > "registered" as a freeing function using DEFINE_FREE() in
> > > > > > <linux/dma-
> > > > > > buf.h>, which has not been done yet.
> > > > > > 
> > > > > > That would mean carrying a dma-buf specific patch in your
> > > > > > tree,
> > > > > > are you
> > > > > > OK with that?
> > > > > Needs an ACK from appropriate maintainer, but otherwise I'm
> > > > > fine
> > > > > doing
> > > > > so.  Alternative is to circle back to this later after this
> > > > > code is
> > > > > upstream.
> > > > Separate patches for that please, the autocleanup feature is so
> > > > new
> > > > that
> > > > I'm not 100% convinced that everything works out smoothly from
> > > > the
> > > > start.
> > > Separate patches is a given, did you mean outside this patchset?
> > > Because I can send a separate patchset that introduces scope-
> > > based
> > > management for dma_fence and dma_buf, but then it won't have
> > > users.
> > 
> > Outside of the patchset, this is essentially brand new stuff.
> > 
> > IIRC we have quite a number of dma_fence selftests and sw_sync
> > which
> > is 
> > basically code inside the drivers/dma-buf directory only there for 
> > testing DMA-buf functionality.
> > 
> > Convert those over as well and I'm more than happy to upstream this
> > change.
> 
> Well there is very little to convert there; you can use scope-based
> management when the unref is done in all exit points of the
> functional
> block, and the only place I could find that does that in drivers/dma-
> buf/ was in dma_fence_chain_enable_signaling() in dma-fence-chain.c.

Actually - not even that, since it doesn't call dma_fence_get() and
dma_fence_put() on the same fence.

So I cannot use it anywhere in drivers/dma-buf/.

-Paul