linux-kernel - Re: [PATCH] asm-generic: add dma-mapping-linear.h

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Message-ID: <20090601104353.GA25391@flint.arm.linux.org.uk>
Date:	Mon, 1 Jun 2009 11:43:53 +0100
From:	Russell King <rmk+lkml@....linux.org.uk>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>,
	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org
Subject: Re: [PATCH] asm-generic: add dma-mapping-linear.h

On Mon, Jun 01, 2009 at 11:28:09AM +0100, Arnd Bergmann wrote:
> On Monday 01 June 2009, Russell King wrote:
> > On Mon, Jun 01, 2009 at 05:08:09PM +0900, FUJITA Tomonori wrote:
> > > This adds a version of the dma-mapping API to asm-generic that can be
> > > used by most architectures that only need a linear mapping.
> > 
> > It depends what is meant by "linear mapping".
> > 
> > If that's just a way of saying "all that needs to be done for the
> > DMA streaming APIs is to flush the cache" then the vast majority of
> > ARMs fall into that category.
> 
> Right. You can probably split out the arm dma-mapping.h implementation
> into the dmabounce version and a version that falls back to my
> asm-generic code.
> 
> One feature that the arm code currently has that I'm still missing is
> highmem support, which seems to be relatively complex in arm
> (three different implementations). Not sure how to best fit that in there.

Err - there's only one highmem implementation on ARM.

Anyway, as I hinted, things in this area will most likely become more
complex in the near future, so any unification of the ARM dma-mapping
will have to be undone.

Let's wait for the ARMv7 support to mature before trying to unify too
much.

-- 
Russell King
 Linux kernel    2.6 ARM Linux   - http://www.arm.linux.org.uk/
 maintainer of:
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