linux-kernel - Re: [PATCH/RFC 4/4] common: dma-mapping: Move dma_common

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Date:	Sun, 13 Jan 2013 11:40:12 +0100
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	Marek Szyprowski <m.szyprowski@...sung.com>
Cc:	linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-media@...r.kernel.org, linux-m68k@...r.kernel.org
Subject: Re: [PATCH/RFC 4/4] common: dma-mapping: Move dma_common_*() to <linux/dma-mapping.h>

Hi Marek,

On Wed, Jan 2, 2013 at 3:22 PM, Marek Szyprowski
<m.szyprowski@...sung.com> wrote:
> On 12/28/2012 8:23 PM, Geert Uytterhoeven wrote:
>> dma_common_mmap() and dma_common_get_sgtable() are defined in
>> drivers/base/dma-mapping.c, and always compiled if CONFIG_HAS_DMA=y.
>>
>> However, their forward declarations and the inline functions defined on
>> top
>> of them (dma_mmap_attrs(), dma_mmap_coherent(), dma_mmap_writecombine(),
>> dma_get_sgtable_attrs()), dma_get_sgtable()) are in
>> <asm-generic/dma-mapping-common.h>, which is not included by all
>> architectures supporting CONFIG_HAS_DMA=y.  There exist no alternative
>> implementations.
>>
>> Hence for e.g. m68k allmodconfig, I get:
>>
>> drivers/media/v4l2-core/videobuf2-dma-contig.c: In function ‘vb2_dc_mmap’:
>> drivers/media/v4l2-core/videobuf2-dma-contig.c:204: error: implicit
>> declaration of function ‘dma_mmap_coherent’
>> drivers/media/v4l2-core/videobuf2-dma-contig.c: In function
>> ‘vb2_dc_get_base_sgt’:
>> drivers/media/v4l2-core/videobuf2-dma-contig.c:387: error: implicit
>> declaration of function ‘dma_get_sgtable’
>>
>> To fix this
>>    - Move the forward declarations and inline definitions to
>>      <linux/dma-mapping.h>, so all CONFIG_HAS_DMA=y architectures can use
>>      them,
>>    - Replace the hard "BUG_ON(!ops)" checks for dma_map_ops by soft
>> checks,
>>      so architectures can fall back to the common code by returning NULL
>>      from their get_dma_ops(). Note that there are no "BUG_ON(!ops)"
>> checks
>>      in other functions in <asm-generic/dma-mapping-common.h>,
>>    - Make "struct dma_map_ops *ops" const while we're at it.
>
>
> I think that more appropriate way of handling it is to avoid dma_map_ops
> based
> calls (those archs probably have some reasons why they don't use it at all)
> and
> provide static inline stubs which call dma_common_mmap and
> dma_common_get_sgtable.

OK, I'll do that.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds
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