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

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Message-ID: <1358177872.4357.53.camel@t520.localdomain>
Date:	Mon, 14 Jan 2013 10:37:52 -0500
From:	Mark Salter <msalter@...hat.com>
To:	Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:	linux-arch@...r.kernel.org, linux-c6x-dev@...ux-c6x.org,
	linux-kernel@...r.kernel.org,
	Marek Szyprowski <m.szyprowski@...sung.com>
Subject: Re: [Linux-c6x-dev] [PATCH 3/9] c6x: Provide dma_mmap_coherent()
 and dma_get_sgtable()

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


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