Subject: Re: can device drivers return non-ram via vm_ops->nopage?
From: David Woodhouse <dwmw2@infradead.org>
To: William Lee Irwin III <wli@holomorphy.com>
Cc: rmk@arm.linux.org.uk, Andrew Morton <akpm@osdl.org>,
       Andrea Arcangeli <andrea@suse.de>, linux-kernel@vger.kernel.org,
       torvalds@osdl.org
In-Reply-To: <20040320224500.GP2045@holomorphy.com>
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Date: Sun, 21 Mar 2004 20:45:14 +0000
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On Sat, 2004-03-20 at 14:45 -0800, William Lee Irwin III wrote:
> This is the exact opposite of what I'd hoped come of this discussion.
> ISTR something about remap_area_pages() missing several pieces, but
> I pretty much need some kind of clarification to know what. Well, that,
> and I presumed your fixups for ALSA were headed toward mainline
> regardless after coping with whatever issue dwmw2 had (e.g. returning
> pfn's or something).

My request was that we shouldn't assume an architecture will have a
'struct page' corresponding to whatever it chooses to return from
dma_alloc_coherent(). 

There are machines where DMA to/from main memory _cannot_ be coherent
but we have some memory elsewhere, perhaps some SRAM which itself is
hanging off an I/O bus somewhere, which can be used. One of my toys is
currently running with dma_alloc_coherent() giving out memory from a PCI
video card, in fact.

Using a PFN should be OK.

-- 
dwmw2


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