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

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Date:	Mon, 18 May 2009 19:45:04 +0900
From:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
To:	arnd@...db.de
Cc:	jgarzik@...ox.com, hancockrwd@...il.com, htejun@...il.com,
	fujita.tomonori@....ntt.co.jp, 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 Sun, 17 May 2009 22:45:21 +0000
Arnd Bergmann <arnd@...db.de> wrote:

> h8300 and m32r currently do not provide a DMA mapping API
> and therefore cannot use the ATA drivers. This adds a
> generic version of dma-mapping.h for architectures that
> have none or very minimal actual support for DMA in hardware
> and makes the two architectures use it.
> 
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
> On Sunday 17 May 2009 20:05:54 Jeff Garzik wrote:
> 
> > That's what needs to happen.  We provide no-op functions for e.g. PCI 
> > and x86 DMI, for platforms where this support does not exist.
> > 
> > Pretty much all architectures support some form of ATA.  m68k, m32r, 
> > h8300 and microblaze all have IDE interface, which means that libata 
> > needs to work on that platform.
> > 
> > The only !ATA arch in the entire kernel is s390, AFAICT.
> 
> m68k only defines NO_DMA for Sun3 and Dragonball. Sun3 does
> not have ATA, Dragonball could probably just enable HAS_DMA.
> 
> ---
>  arch/h8300/Kconfig                   |    2 +-
>  arch/h8300/include/asm/dma-mapping.h |    1 +
>  arch/m32r/Kconfig                    |    2 +-
>  arch/m32r/include/asm/dma-mapping.h  |    1 +
>  include/asm-generic/dma-mapping.h    |  399 ++++++++++++++++++++++++++++++++++
>  5 files changed, 403 insertions(+), 2 deletions(-)
>  create mode 100644 arch/h8300/include/asm/dma-mapping.h
>  create mode 100644 arch/m32r/include/asm/dma-mapping.h
>  create mode 100644 include/asm-generic/dma-mapping.h
> 
> diff --git a/arch/h8300/Kconfig b/arch/h8300/Kconfig
> index 9420648..36a037d 100644
> --- a/arch/h8300/Kconfig
> +++ b/arch/h8300/Kconfig
> @@ -74,7 +74,7 @@ config NO_IOPORT
>  	def_bool y
>  
>  config NO_DMA
> -	def_bool y
> +	def_bool n
>  
>  config ISA
>  	bool
> diff --git a/arch/h8300/include/asm/dma-mapping.h b/arch/h8300/include/asm/dma-mapping.h
> new file mode 100644
> index 0000000..e7e1690
> --- /dev/null
> +++ b/arch/h8300/include/asm/dma-mapping.h
> @@ -0,0 +1 @@
> +#include <asm-generic/dma-mapping.h>
> diff --git a/arch/m32r/Kconfig b/arch/m32r/Kconfig
> index cabba33..57ad603 100644
> --- a/arch/m32r/Kconfig
> +++ b/arch/m32r/Kconfig
> @@ -35,7 +35,7 @@ config NO_IOPORT
>  	def_bool y
>  
>  config NO_DMA
> -	def_bool y
> +	def_bool n
>  
>  config HZ
>  	int
> diff --git a/arch/m32r/include/asm/dma-mapping.h b/arch/m32r/include/asm/dma-mapping.h
> new file mode 100644
> index 0000000..e7e1690
> --- /dev/null
> +++ b/arch/m32r/include/asm/dma-mapping.h
> @@ -0,0 +1 @@
> +#include <asm-generic/dma-mapping.h>
> diff --git a/include/asm-generic/dma-mapping.h b/include/asm-generic/dma-mapping.h
> new file mode 100644
> index 0000000..5a14fed
> --- /dev/null
> +++ b/include/asm-generic/dma-mapping.h
> @@ -0,0 +1,399 @@
> +#ifndef _ASM_GENERIC_DMA_MAPPING_H
> +#define _ASM_GENERIC_DMA_MAPPING_H
> +/*
> + * This provides a no-op variant of the DMA mapping API,
> + * for use by architectures that do not actually support
> + * DMA, or that are fully consistent and linear-mapped
> + * in their DMA implementation.
> + */
> +
> +#include <asm/scatterlist.h>
> +
> +/*
> + * If any driver asks for DMA, it's not supported.
> + */
> +#ifndef dma_supported
> +static inline int
> +dma_supported(struct device *dev, u64 mask)
> +{
> +	return 0;
> +}
> +#endif

NACK'ed, sorry.

- these idndef tricks are really ugly and wrong.

- these functions are not generic at all.

- it's confusing to have two ways to handle this issue;
dma-mapping-broken.h and dma-mapping.h.
--
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