linux-kernel - Re: [RFCv3 2/2] dma-buf: add helpers for sharing attacher constraints with dma-parms

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Message-ID: <20150203143715.GQ8656@n2100.arm.linux.org.uk>
Date:	Tue, 3 Feb 2015 14:37:15 +0000
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Rob Clark <robdclark@...il.com>
Cc:	Sumit Semwal <sumit.semwal@...aro.org>,
	LKML <linux-kernel@...r.kernel.org>,
	"linux-media@...r.kernel.org" <linux-media@...r.kernel.org>,
	DRI mailing list <dri-devel@...ts.freedesktop.org>,
	Linaro MM SIG Mailman List <linaro-mm-sig@...ts.linaro.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Linaro Kernel Mailman List <linaro-kernel@...ts.linaro.org>,
	Tomasz Stanislawski <stanislawski.tomasz@...glemail.com>,
	Robin Murphy <robin.murphy@....com>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Daniel Vetter <daniel@...ll.ch>
Subject: Re: [RFCv3 2/2] dma-buf: add helpers for sharing attacher
 constraints with dma-parms

On Tue, Feb 03, 2015 at 09:04:03AM -0500, Rob Clark wrote:
> Since I'm stuck w/ an iommu, instead of built in mmu, my plan was to
> drop use of dma-mapping entirely (incl the current call to dma_map_sg,
> which I just need until we can use drm_cflush on arm), and
> attach/detach iommu domains directly to implement context switches.
> At that point, dma_addr_t really has no sensible meaning for me.

So how do you intend to import from a subsystem which only gives you
the dma_addr_t?

If you aren't passing system memory, you have no struct page.  You can't
fake up a struct page.  What this means is that struct scatterlist can't
represent it any other way.

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