linux-kernel - Re: [PATCH -mm] uml: disable CONFIG_HAS

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Message-Id: <20100906195113T.fujita.tomonori@lab.ntt.co.jp>
Date:	Mon, 6 Sep 2010 19:55:14 +0900
From:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
To:	sam@...nborg.org
Cc:	fujita.tomonori@....ntt.co.jp, akpm@...ux-foundation.org,
	miklos@...redi.hu, jdike@...toit.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH -mm] uml: disable CONFIG_HAS_DMA

On Sat, 4 Sep 2010 13:18:25 +0200
Sam Ravnborg <sam@...nborg.org> wrote:

> On Sat, Sep 04, 2010 at 07:31:26PM +0900, FUJITA Tomonori wrote:
> > On Sat, 4 Sep 2010 12:13:13 +0200
> > Sam Ravnborg <sam@...nborg.org> wrote:
> > 
> > > On Sat, Sep 04, 2010 at 06:17:56PM +0900, FUJITA Tomonori wrote:
> > > > I think that it's better to detect DMA misuse at build time rather
> > > > than calling BUG_ON. Architectures that can't do DMA need to disable
> > > > CONFIG_HAS_DMA.
> > > > 
> > > > Signed-off-by: FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
> > > > ---
> > > >  arch/um/Kconfig.um                |    3 +
> > > >  arch/um/defconfig                 |    1 -
> > > >  arch/um/include/asm/dma-mapping.h |  112 -------------------------------------
> > > >  3 files changed, 3 insertions(+), 113 deletions(-)
> > > >  delete mode 100644 arch/um/include/asm/dma-mapping.h
> > > > 
> > > > diff --git a/arch/um/Kconfig.um b/arch/um/Kconfig.um
> > > > index ec2b8da..3de40b8 100644
> > > > --- a/arch/um/Kconfig.um
> > > > +++ b/arch/um/Kconfig.um
> > > > @@ -147,3 +147,6 @@ config KERNEL_STACK_ORDER
> > > >  	  This option determines the size of UML kernel stacks.  They will
> > > >  	  be 1 << order pages.  The default is OK unless you're running Valgrind
> > > >  	  on UML, in which case, set this to 3.
> > > > +
> > > > +config HAS_DMA
> > > > +       def_bool n
> > > 
> > > Other archs define NO_DMA to say they do not have DMA.
> > > We should do it the same way for um.
> > 
> > Defining NO_DMA affects any code? In other words, we can kill NO_DMA
> > definition?
> 
> NO_DMA affects HAS_DMA.
> 
> HAS_DMA is defined like this:
> 
> config HAS_DMA
>         boolean
>         depends on !NO_DMA
>         default y

Ah, I overlooked this. I'll send the updated patch.

Thanks a lot!
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