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

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Date:	Sun, 27 Nov 2011 00:59:30 -0600
From:	Rob Clark <robdclark@...il.com>
To:	Daniel Vetter <daniel@...ll.ch>
Cc:	Dave Airlie <airlied@...il.com>,
	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
Subject: Re: [Linaro-mm-sig] [RFC 1/2] dma-buf: Introduce dma buffer sharing mechanism

On Sat, Nov 26, 2011 at 8:00 AM, Daniel Vetter <daniel@...ll.ch> wrote:
> On Fri, Nov 25, 2011 at 17:28, Dave Airlie <airlied@...il.com> wrote:
>> I've rebuilt my PRIME interface on top of dmabuf to see how it would work,
>>
>> I've got primed gears running again on top, but I expect all my object
>> lifetime and memory ownership rules need fixing up (i.e. leaks like a
>> sieve).
>>
>> http://cgit.freedesktop.org/~airlied/linux/log/?h=drm-prime-dmabuf
>>
>> has the i915/nouveau patches for the kernel to produce the prime interface.
>
> I've noticed that your implementations for get_scatterlist (at least
> for the i915 driver) doesn't return the sg table mapped into the
> device address space. I've checked and the documentation makes it
> clear that this should be the case (and we really need this to support
> certain insane hw), but the get/put_scatterlist names are a bit
> misleading. Proposal:
>
> - use struct sg_table instead of scatterlist like you've already done
> in you branch. Simply more consistent with the dma api.

yup

> - rename get/put_scatterlist into map/unmap for consistency with all
> the map/unmap dma api functions. The attachement would then serve as
> the abstract cookie to the backing storage, similar to how struct page
> * works as an abstract cookie for dma_map/unmap_page. The only special
> thing is that struct device * parameter because that's already part of
> the attachment.

yup

> - add new wrapper functions dma_buf_map_attachment and
> dma_buf_unmap_attachement to hide all the pointer/vtable-chasing that
> we currently expose to users of this interface.

I thought that was one of the earlier comments on the initial dmabuf
patch, but either way: yup

BR,
-R

> Comments?
>
> Cheers, Daniel
> --
> Daniel Vetter
> daniel.vetter@...ll.ch - +41 (0) 79 364 57 48 - http://blog.ffwll.ch
> --
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