linux-kernel - Re: [PATCH] ata: libata depends on HAS

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Message-Id: <200905151316.31521.arnd@arndb.de>
Date:	Fri, 15 May 2009 13:16:30 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Tejun Heo <htejun@...il.com>
Cc:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>,
	hancockrwd@...il.com, alan@...rguk.ukuu.org.uk, flar@...andria.com,
	schmitz@...phys.uni-duesseldorf.de, linux-kernel@...r.kernel.org,
	jgarzik@...ox.com, 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] ata: libata depends on HAS_DMA

On Friday 15 May 2009, Tejun Heo wrote:
> FUJITA Tomonori wrote:
> > Can libata call dma_supported() per device to decide DMA or PIO mode?
> > Then, we can solve this problem by add dummy DMA API (just calls BUG)
> > on such architectures, without Kconfig magic or adding ifdef (like the
> > old ide stack does), I think.

That would be the !CONFIG_PCI half of the old
include/asm-generic/dma-mapping.h file that you just removed,
right?

In general, I'd prefer keeping the asm-generic/dma-mapping-broken.h
implementation that gives us a compile-time error, but maybe there
is an even better option based on the mn10300 implementation which
basically pretends everything works with just page_to_phys() mappings.

> Sure it can.  Which specific drivers are we talking about?

The main problem is libata-core.c, which references DMA mapping
API calls that are only implemented on architectures setting
CONFIG_HAS_DMA.

	Arnd <><
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