[Linaro-mm-sig] [RFC 2/2] ARM: initial proof-of-concept IOMMU mapper for DMA-mapping

[Ramirez Luna, Omar]

Hi Marek,

> Add initial proof of concept implementation of DMA-mapping API for
> devices that have IOMMU support. Right now only dma_alloc_coherent,
> dma_free_coherent and dma_mmap_coherent functions are supported.
>
> Signed-off-by: Marek Szyprowski <m.szyprowski at samsung.com>
> Signed-off-by: Kyungmin Park <kyungmin.park at samsung.com>
> ---
...
> diff --git a/arch/arm/include/asm/dma-iommu.h b/arch/arm/include/asm/dma-iommu.h
> new file mode 100644
> index 0000000..c246ff3
> --- /dev/null
> +++ b/arch/arm/include/asm/dma-iommu.h
...
> +int __init arm_iommu_assign_device(struct device *dev, dma_addr_t base, dma_addr_t size);

__init causes a panic if the iommu is assigned after boot.

In OMAP3 the iommu driver controls isp and dsp address spaces, it is
loaded until any of those 2 drivers is needed.

> diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c
> index f8c6972..b6397c1 100644
> --- a/arch/arm/mm/dma-mapping.c
> +++ b/arch/arm/mm/dma-mapping.c
...
> +static void *arm_iommu_alloc_attrs(struct device *dev, size_t size,
> +           dma_addr_t *handle, gfp_t gfp, struct dma_attrs *attrs)
> +{
> +       struct dma_iommu_mapping *mapping = dev->archdata.mapping;
> +       struct page **pages;
> +       void *addr = NULL;
> +       pgprot_t prot;
> +
> +       if (dma_get_attr(DMA_ATTR_WRITE_COMBINE, attrs))
> +               prot = pgprot_writecombine(pgprot_kernel);
> +       else
> +               prot = pgprot_dmacoherent(pgprot_kernel);
> +
> +       arm_iommu_init(dev);

I found useful to call arm_iommu_init inside arm_iommu_assign_device
instead. So, then gen_pool is created only once without the
mapping->pool check, instead of relying on the call to ...alloc_attrs,
which in my case I never use because I'm implementing
iommu_map|unmap_sg functions to see how it goes with the dma mapping.

Regards,

Omar