linux-kernel - Re: [Linaro-mm-sig] [RFC 1/2] dma-buf: Introduce dma buffer sharing mechanism

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Date:	Wed, 12 Oct 2011 15:01:37 +0100
From:	Dave Airlie <airlied@...il.com>
To:	Rob Clark <robdclark@...il.com>
Cc:	Sumit Semwal <sumit.semwal@...com>, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-mm@...ck.org,
	linaro-mm-sig@...ts.linaro.org, dri-devel@...ts.freedesktop.org,
	linux-media@...r.kernel.org, linux@....linux.org.uk, arnd@...db.de,
	jesse.barker@...aro.org, daniel@...ll.ch
Subject: Re: [Linaro-mm-sig] [RFC 1/2] dma-buf: Introduce dma buffer sharing mechanism

> But then we'd need a different set of accessors for every different
> drm/v4l/etc driver, wouldn't we?

Not any more different than you need for this, you just have a new
interface that you request a sw object from,
then mmap that object, and underneath it knows who owns it in the kernel.

mmap just feels wrong in this API, which is a buffer sharing API not a
buffer mapping API.

> I guess if sharing a buffer between multiple drm devices, there is
> nothing stopping you from having some NOT_DMABUF_MMAPABLE flag you
> pass when the buffer is allocated, then you don't have to support
> dmabuf->mmap(), and instead mmap via device and use some sort of
> DRM_CPU_PREP/FINI ioctls for synchronization..

Or we could make a generic CPU accessor that we don't have to worry about.

Dave.
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