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    SubjectRe: How to get the physical page addresses from a kernel virtual address for DMA SG List?
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    You are trying to do it backwards. You need to have your driver
    use get_dma_pages() to acquire pages suitable for DMA. Your
    driver then impliments mmap().

    The user-mode application then mmaps() the dma-able pages into
    its address-space. FYI, the pages may be from anywhere, some
    archs can only DMA to/from memory below 16MB. The pages do not have
    to be continuous because you will build a scatter-list for
    the DMA engine and you will mmap() the pages so they are
    contiguous to the user. Also 400 Megabytes is absurd.

    On Thu, 4 Aug 2005, Clemens Koller wrote:

    > Hello!
    >
    > This might be an FAQ - I've got several ideas from googling
    > around for days and reading 'Linux Device Drivers' or
    > 'Understanding The Linux Kernel' which are both really good
    > books. However I am not really sure of how to do it on the latest
    > linux-2.6.
    >
    > I am currently working on a dma driver for a ppc32 system.
    > The idea is that a userspace app allocates a big contigous
    > chunk of memory (i.e. 400MBytes, user virtual mem) and tells
    > my dma's char driver via ioctl the pointer to that memory.
    >
    > In the driver I can now use that (void __user *) casted address
    > as a kernel virtual address, right? It's contigous there and I can
    > do a memcpy() to get data to userspace simliar to a copy_to_user().
    > fine!
    >
    > But I want to setup a scatter/gather DMA list and blow my data
    > directly into the applications physical pages.
    >
    > What's the best way to setup the dma_sg_list?
    > I have checked several things to get the pages and physical addresses
    > but with no real success now:
    > get_user_page()
    > vmalloc_to_page()
    > kvirt_to_bus() (deprecated?)
    > virt_to_phys()
    > virt_to_bus()
    >
    > Or do I need to remap the whole thing before I can get all the pages and
    > physical addresses?
    > remap_page_range()
    > remap_pfn_range()
    > map_user_kiobuf()
    > unmap_kiobuf()
    >
    > Or do I need the direct-io stuff or the block-io?
    > How do I need to alloc the mem in my app? (get_pages()?)
    > How do I need to lock the memory to make sure it's in phys memory? (mlockall()?)
    > Can somebody please put some light on what's _the_ way to do that on the
    > latest 2.6 kernels? I am pretty much confused which functions are current
    > and okay to use to solve my problem.
    > Pointers to some code is also very welcome. But it should be _current_.
    > I've spent already a lot of time reading outdated things. :-(
    >
    > Best regards,
    >
    > Clemens Koller
    > _______________________________
    > R&D Imaging Devices
    > Anagramm GmbH
    > Rupert-Mayer-Str. 45/1
    > 81379 Muenchen
    > Germany
    >
    > http://www.anagramm.de
    > Phone: +49-89-741518-50
    > Fax: +49-89-741518-19
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    > Please read the FAQ at http://www.tux.org/lkml/
    >

    Cheers,
    Dick Johnson
    Penguin : Linux version 2.6.12 on an i686 machine (5537.79 BogoMips).
    Warning : 98.36% of all statistics are fiction.
    .
    I apologize for the following. I tried to kill it with the above dot :

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