linux-kernel - Re: [PATCH 8/9] parisc: Provide dma_mmap_coherent() and dma_get

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Message-ID: <CAMuHMdVvRmNZS_L8-kYm4VGexD3h=nW4wC266cu7VAxJFx+-oA@mail.gmail.com>
Date:	Sun, 13 Jan 2013 14:12:24 +0100
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	James Bottomley <James.Bottomley@...senpartnership.com>
Cc:	linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	linux-parisc@...r.kernel.org
Subject: Re: [PATCH 8/9] parisc: Provide dma_mmap_coherent() and dma_get_sgtable()

On Sun, Jan 13, 2013 at 12:36 PM, James Bottomley
<James.Bottomley@...senpartnership.com> wrote:
> On Sun, 2013-01-13 at 11:44 +0100, Geert Uytterhoeven wrote:
>> parisc/allmodconfig:
>>
>> 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>.
>>
>> Parisc does not use dma_map_ops, hence it should implement them as inline
>> stubs using dma_common_mmap() and dma_common_get_sgtable().
>>
>> Signed-off-by: Geert Uytterhoeven <geert@...ux-m68k.org>
>> Cc: Marek Szyprowski <m.szyprowski@...sung.com>
>> Cc: linux-parisc@...r.kernel.org
>> ---
>>  arch/parisc/include/asm/dma-mapping.h |   10 ++++++++++
>>  1 files changed, 10 insertions(+), 0 deletions(-)
>>
>> diff --git a/arch/parisc/include/asm/dma-mapping.h b/arch/parisc/include/asm/dma-mapping.h
>> index 467bbd5..1fac0bf 100644
>> --- a/arch/parisc/include/asm/dma-mapping.h
>> +++ b/arch/parisc/include/asm/dma-mapping.h
>> @@ -238,4 +238,14 @@ void * sba_get_iommu(struct parisc_device *dev);
>>  /* At the moment, we panic on error for IOMMU resource exaustion */
>>  #define dma_mapping_error(dev, x)    0
>>
>> +/* drivers/base/dma-mapping.c */
>> +extern int dma_common_mmap(struct device *dev, struct vm_area_struct *vma,
>> +                        void *cpu_addr, dma_addr_t dma_addr, size_t size);
>> +extern int dma_common_get_sgtable(struct device *dev, struct sg_table *sgt,
>> +                               void *cpu_addr, dma_addr_t dma_addr,
>> +                               size_t size);
>> +
>> +#define dma_mmap_coherent(d, v, c, h, s) dma_common_mmap(d, v, c, h, s)
>> +#define dma_get_sgtable(d, t, v, h, s) dma_common_get_sgtable(d, t, v, h, s)
>
> What is the documentation around these functions?  The name sounds
> suspiciously like you want a mapping of a buffer coherent between kernel
> and user space, which doesn't seem possible for us given the API.  We're
> a VIPT architecture, so the only way we can do this is to have the
> actual vma user space address be congruent with cpu_addr.  How do we do
> that if the vma and kernel addresses are already fixed?

I was already afraid of this when seeing the "coherent" in the naming...

> In other words, either the interface is unusable by parisc, or the
> common code definitely won't work for us.

So you probably want a static inline function that returns -EINVAL for now?

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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