linux-kernel - Re: [Linux-c6x-dev] [PATCH 3/9] c6x: Provide dma_mmap_coherent() and dma_get

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Message-ID: <CAMuHMdWjZAY19GPpjoXKfWb3pOp2RbZXDvb4nr5pMmjEMFuB4w@mail.gmail.com>
Date:	Tue, 15 Jan 2013 10:13:46 +0100
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	Marek Szyprowski <m.szyprowski@...sung.com>
Cc:	Mark Salter <msalter@...hat.com>,
	Vineet Gupta <Vineet.Gupta1@...opsys.com>,
	linux-arch@...r.kernel.org, linux-c6x-dev@...ux-c6x.org,
	linux-kernel@...r.kernel.org
Subject: Re: [Linux-c6x-dev] [PATCH 3/9] c6x: Provide dma_mmap_coherent() and dma_get_sgtable()

Marek?

On Tue, Jan 15, 2013 at 5:16 AM, Vineet Gupta
<Vineet.Gupta1@...opsys.com> wrote:
> On Monday 14 January 2013 09:07 PM, Mark Salter wrote:
>> On Sun, 2013-01-13 at 11:44 +0100, Geert Uytterhoeven wrote:
>>> c6x/allmodconfig (assumed):
>>>
>>> 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’
>>>
>>> For architectures using dma_map_ops, dma_mmap_coherent() and
>>> dma_get_sgtable() are provided in <asm-generic/dma-mapping-common.h>.
>>>
>>> C6x does not use dma_map_ops, hence it should implement them as inline
>>> stubs using dma_common_mmap() and dma_common_get_sgtable().
>>>
>>
>> So are dma_mmap_coherent() and dma_get_sgtable() part of the DMA API
>> now? I don't them in Documentation/DMA*.txt anywhere.
>>
>> Why does the default dma_common_mmap() for !CONFIG_MMU return an
>> error?
>>
>> Wouldn't it be better to provide default implementations that an arch
>> could override rather than having to patch all "no dma_map_ops"
>> architectures?
>>
>> --Mark
>>
>>
>
> Speaking for the still-reviewed ARC Port, I completely agree with Mark.

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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