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

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Message-Id: <20090519074355P.fujita.tomonori@lab.ntt.co.jp>
Date:	Tue, 19 May 2009 07:44:08 +0900
From:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
To:	arnd@...db.de
Cc:	fujita.tomonori@....ntt.co.jp, jgarzik@...ox.com,
	hancockrwd@...il.com, htejun@...il.com, alan@...rguk.ukuu.org.uk,
	flar@...andria.com, schmitz@...phys.uni-duesseldorf.de,
	linux-kernel@...r.kernel.org, linux-ide@...r.kernel.org,
	takata@...ux-m32r.org, geert@...ux-m68k.org,
	linux-m68k@...r.kernel.org, ysato@...rs.sourceforge.jp
Subject: Re: [PATCH] asm-generic: add a dma-mapping.h file

On Mon, 18 May 2009 16:45:24 +0200
Arnd Bergmann <arnd@...db.de> wrote:

> On Monday 18 May 2009, FUJITA Tomonori wrote:
> > 
> > NACK'ed, sorry.
> 
> I had no idea how hard it would get to fix a simple
> allyesconfig build error. This is the third time
> that a new approach to getting ATA to build on all
> platforms is gets a NAK...
> 
> > - these idndef tricks are really ugly and wrong.
> > - these functions are not generic at all.
> 
> I was trying to do two things at once:
> 
> - provide a default implementation for each function
>   that an architecture can override, therefore the
>   #ifdef magic.

I know what you tried with #ifdef but having something like '#define
dma_map_sg' in arch's dma-mapping.h is unacceptable.


> - Have a minimal working implementation of the API
>   that at least makes sense for architectures that
>   do not support DMA, but want to share some of the
>   code.

Well, it might make sense but we don't call architectures that don't
support DMA 'generic'.


> Ten of the existing architectures simply try do a
> linear mapping, and that should easily be possible
> in a generic way not too different from what I posted.

Your proposal doesn't work with arch/x86/kernel/pci-nommu.c, which
is trying a linear mapping, what you are talking about.


> Would you agree to a patch that works with the same
> code on e.g. arm, microblaze, mn10300 and sh and
> uses only a few #ifdefs?

Having such helper for a linear mapping might be helpful but your
approach is wrong.

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