Date: Sun, 21 Mar 2004 15:11:58 -0800 (PST)
From: Linus Torvalds <torvalds@osdl.org>
To: Russell King <rmk+lkml@arm.linux.org.uk>
cc: Jeff Garzik <jgarzik@pobox.com>, David Woodhouse <dwmw2@infradead.org>,
       Christoph Hellwig <hch@infradead.org>,
       William Lee Irwin III <wli@holomorphy.com>,
       Andrew Morton <akpm@osdl.org>, Andrea Arcangeli <andrea@suse.de>,
       linux-kernel@vger.kernel.org
Subject: Re: can device drivers return non-ram via vm_ops->nopage?
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On Sun, 21 Mar 2004, Russell King wrote:
> 
> Remember that we're fond of telling driver writers to use scatter gather
> lists rather than grabbing one large contiguous memory chunk...  So
> they did exactly as we told them.  Using pci_alloc_consistent and/or
> dma_alloc_coherent and built their own scatter lists.

I do think that we should introduce a "map_dma_coherent()" thing, which 
basically takes a list of pages that have been allocated by 
dma_alloc_coherent(), and remaps them into user space. How hard can that 
be?

In fact, on a lot of architectures (well, at least x86, and likely
anything else that doesn't use any IOTLB and just allocates a chunk of
physical memory), I think the "map_dma_coherent()" thing should basically
just become a "remap_page_range()". Ie something like

	#define map_dma_coherent(vma, vaddr, len) \
		remap_page_range(vma, vma->vm_start, __pa(vaddr), len, vma->vm_page_prot)

for the simple case.

Ehh?

		Linus
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