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From: "Dan Williams" <>
To: "Heiko Carstens" <>
Cc: "Andrew Morton" <>,
	"John W. Linville" <>,
	"Kyle McMartin" <>,,,
	"Tejun Heo" <>, "Jeff Garzik" <>,
	"Martin Schwidefsky" <>,,,,,,
	"Cornelia Huck" <>
Subject: Re: [patch] Introduce CONFIG_HAS_DMA.
Date: Fri, 25 May 2007 09:36:31 -0700	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

[ apologies for reviving an old conversation ]

On 2/26/07, Heiko Carstens <> wrote:
> From: Heiko Carstens <>
> Architectures that don't support DMA can say so by adding a
> config NO_DMA to their Kconfig file. This will prevent compilation
> of some dma specific driver code. Also dma-mapping-broken.h isn't
> needed anymore on at least s390.
> This avoids compilation and linking of otherwise dead/broken code.

I went back and read the thread leading up to this patch and I am of
the opinion that John's approach (adding more stubs to
dma-mapping-broken.h:  is needed in
_addition_ to this Kconfig option.  In my particular case I have an
API with a DMA and a non-DMA path written in such a way that the DMA
path can be compiled away.  Without dma-mapping-broken.h support the
API is unnecessarily forced to violate point 2 of
Documentation/SubmittingPatches (#ifdefs are ugly).

In other words let CONFIG_HAS_DMA prevent pure DMA code from being
built, but do not preclude "clever" implementations from calling
broken code.

If there are no objections I plan to resubmit John's changes with the
addition below, which allows CONFIG_HAS_DMA=n architectures to delete
their respective dma-mapping.h file.

diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
index 9a663c6..2dc21cb 100644
--- a/include/linux/dma-mapping.h
+++ b/include/linux/dma-mapping.h
@@ -31,7 +31,11 @@ static inline int valid_dma_direction(int dma_direction)
                (dma_direction == DMA_FROM_DEVICE));

 #include <asm/dma-mapping.h>
+#include <asm-generic/dma-mapping-broken.h>

 /* Backwards compat, remove in 2.7.x */
 #define dma_sync_single                dma_sync_single_for_cpu

  reply	other threads:[~2007-05-25 16:36 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2007-02-23  0:59 [PATCH] dma-mapping-broken.h: flesh-out DMA API stubs John W. Linville
2007-02-23  3:42 ` Heiko Carstens
2007-02-23  6:13   ` Heiko Carstens
2007-02-23  9:50     ` Heiko Carstens
2007-02-23 13:57     ` Kyle McMartin
2007-02-23 14:39       ` John W. Linville
2007-02-26 13:57         ` [patch] Introduce CONFIG_HAS_DMA Heiko Carstens
2007-05-25 16:36           ` Dan Williams [this message]
2007-05-30  9:10             ` Cornelia Huck
2007-05-30 21:40               ` Williams, Dan J
2007-05-30 22:29                 ` [PATCH] dma-mapping: prevent dma dependent code from linking on !HAS_DMA archs Dan Williams
2007-05-31  6:53                 ` [patch] Introduce CONFIG_HAS_DMA Cornelia Huck

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