Date: Mon, 21 Jun 2004 20:18:22 -0700 (PDT)
From: Linus Torvalds <torvalds@osdl.org>
To: Jeff Garzik <jgarzik@pobox.com>
cc: Russell King <rmk+lkml@arm.linux.org.uk>, Takashi Iwai <tiwai@suse.de>,
       Matt Porter <mporter@kernel.crashing.org>,
       Jamey Hicks <jamey.hicks@hp.com>, Ian Molton <spyro@f2s.com>,
       linux-kernel@vger.kernel.org, greg@kroah.com, tony@atomide.com,
       david-b@pacbell.net, joshua@joshuawise.com
Subject: Re: DMA API issues
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On Mon, 21 Jun 2004, Jeff Garzik wrote:
> 
> When I was writing sound/oss/via82cxxx_audio.c, Linus specifically 
> recommended using ->nopage, which worked out quite well (modulo cleaning 
> up VM_xxx flags).

It does need some architecture-specific support for getting the caching
behaviour right, but I do believe that as long as there is some "struct
page" that can be returned, together with a way of setting the
vm_page_prot bits right, it should be ok.

The argument at some point was that some architectures may not even _have_
a "struct page" for DMA memory, since it's not "normal" memory (ie "slow
memory" on m68k). However, I thought we all agreed that such a "struct
page" could be furnished if that architecture wants so support mmap'ing.

		Linus
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