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    SubjectRe: mmap + dma_alloc_coherent
    On Wed, Apr 13, 2005 at 12:43:47PM +0200, Rolf Offermanns wrote:
    > I would like to mmap a kernel buffer, allocated with pci_alloc_consistent()
    > for DMA, to userspace and came up with the following. Since there seem to be
    > some (unresolved) issues (see below) with this and I would like to do the
    > RightThing(TM), I would appreciate your comments about my stuff.

    This has come up before. ARM implements dma_mmap_*() to allow this
    to happen, but it never got propagated to the other architectures.

    Here's the (untested) x86 version. There may be a problem with
    x86 not marking the pages reserved, which is required for
    remap_pfn_range() to work.

    diff -up -x BitKeeper -x ChangeSet -x SCCS -x _xlk -x '*.orig' -x '*.rej' -r orig/arch/i386/kernel/pci-dma.c linux/arch/i386/kernel/pci-dma.c
    --- orig/arch/i386/kernel/pci-dma.c Mon Apr 4 22:52:57 2005
    +++ linux/arch/i386/kernel/pci-dma.c Mon Apr 4 22:44:45 2005
    @@ -49,7 +49,7 @@ void *dma_alloc_coherent(struct device *
    ret = (void *)__get_free_pages(gfp, order);

    if (ret != NULL) {
    - memset(ret, 0, size);
    + memset(ret, 0, PAGE_ALIGN(size));
    *dma_handle = virt_to_phys(ret);
    }
    return ret;
    diff -up -x BitKeeper -x ChangeSet -x SCCS -x _xlk -x '*.orig' -x '*.rej' -r orig/include/asm-i386/dma-mapping.h linux/include/asm-i386/dma-mapping.h
    --- orig/include/asm-i386/dma-mapping.h Mon Apr 4 22:54:41 2005
    +++ linux/include/asm-i386/dma-mapping.h Mon Apr 4 22:48:11 2005
    @@ -16,6 +16,23 @@ void *dma_alloc_coherent(struct device *
    void dma_free_coherent(struct device *dev, size_t size,
    void *vaddr, dma_addr_t dma_handle);

    +static inline int
    +dma_mmap_coherent(struct device *dev, struct vm_area_struct *vma,
    + void *vaddr, dma_addr_t handle, size_t size)
    +{
    + unsigned long offset = vma->vm_pgoff, usize;
    +
    + size = PAGE_ALIGN(size) >> PAGE_SHIFT;
    + usize = (vma->vm_end - vma->vm_start) >> PAGE_SHIFT;
    +
    + if (offset >= size || usize > (size - offset))
    + return -ENXIO;
    +
    + return remap_pfn_range(vma, vma->vm_start,
    + (__pa(vaddr) >> PAGE_SHIFT) + offset,
    + usize << PAGE_SHIFT, vma->vm_page_prot);
    +}
    +
    static inline dma_addr_t
    dma_map_single(struct device *dev, void *ptr, size_t size,
    enum dma_data_direction direction)


    --
    Russell King
    Linux kernel 2.6 ARM Linux - http://www.arm.linux.org.uk/
    maintainer of: 2.6 Serial core
    -
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