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

[Rob Clark <robdclark@gmail.com>]

On Tue, Feb 3, 2015 at 9:37 AM, Russell King - ARM Linux
<linux@arm.linux.org.uk> wrote:
> 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.

Tell the exporter to stop using carveouts, and give me proper memory
instead.. ;-)

Well, at least on these SoC's, I think the only valid use for carveout
memory is the bootloader splashscreen.  And I was planning on just
hanging on to that for myself for fbdev scanout buffer or other
internal (non shared) usage..

BR,
-R

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