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    SubjectRe: [PATCH] asm-generic: add a dma-mapping.h file
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    On Mon, May 18, 2009 at 00:45, Arnd Bergmann <arnd@arndb.de> wrote:
    > --- /dev/null
    > +++ b/include/asm-generic/dma-mapping.h
    > @@ -0,0 +1,399 @@
    > +#ifndef _ASM_GENERIC_DMA_MAPPING_H
    > +#define _ASM_GENERIC_DMA_MAPPING_H
    > +/*
    > + * This provides a no-op variant of the DMA mapping API,
    > + * for use by architectures that do not actually support
    > + * DMA, or that are fully consistent and linear-mapped
    > + * in their DMA implementation.
    > + */
    > +
    > +#include <asm/scatterlist.h>
    > +
    > +/*
    > + * If any driver asks for DMA, it's not supported.
    > + */
    > +#ifndef dma_supported
    > +static inline int
    > +dma_supported(struct device *dev, u64 mask)
    > +{
    > +       return 0;
    > +}
    > +#endif
    > +
    > +#ifndef dma_set_mask
    > +static inline int
    > +dma_set_mask(struct device *dev, u64 dma_mask)
    > +{
    > +       if (!dev->dma_mask || !dma_supported(dev, dma_mask))
    > +               return -EIO;
    > +
    > +       *dev->dma_mask = dma_mask;
    > +       return 0;
    > +}
    > +#endif
    > +
    > +/**
    > + * dma_alloc_coherent - allocate consistent memory for DMA
    > + * @dev: valid struct device pointer, or NULL for ISA and EISA-like devices
    > + * @size: required memory size
    > + * @handle: bus-specific DMA address
    > + *
    > + * Allocate some uncached, unbuffered memory for a device for
    > + * performing DMA.  This function allocates pages, and will
    > + * return the CPU-viewed address, and sets @handle to be the
    > + * device-viewed address.
    > + */
    > +#ifndef dma_alloc_coherent
    > +static inline void *
    > +dma_alloc_coherent(struct device *dev, size_t size, dma_addr_t *dma_handle,
    > +                  gfp_t flag)
    > +{
    > +       void *virt = kmalloc(size, flag);

    kmalloc() may fail.

    > +       *dma_handle = virt_to_phys(virt);

    Not all variants of virt_to_phys() may handle the NULL case very well.
    I took a statistically invalid sample: some just cast to unsigned
    long, other subtract PAGE_OFFSET.

    Gr{oetje,eeting}s,

    Geert

    --
    Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-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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