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

[FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>]

On Mon, 18 May 2009 16:45:24 +0200
Arnd Bergmann <arnd@arndb.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.