Re: [PATCH] asm-generic: add a dma-mapping.h file

[Geert Uytterhoeven <geert@linux-m68k.org>]

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