ARM linux DMA alloc question - Hardware

This is a discussion on ARM linux DMA alloc question - Hardware ; Hi, I am using Linux kernel 2.6.12.6 for my ARM project. I use dma_alloc_writecombine() to allocate DMA uncached memory. The default consistent memory is define in CONSISTENT_BASE and CONSISTENT_END as 0xffc00000 and 0xffe00000 which is 2MB. Since I need about ...

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Thread: ARM linux DMA alloc question

  1. ARM linux DMA alloc question

    Hi,

    I am using Linux kernel 2.6.12.6 for my ARM project.
    I use dma_alloc_writecombine() to allocate DMA uncached
    memory. The default consistent memory is define in
    CONSISTENT_BASE and CONSISTENT_END as 0xffc00000 and
    0xffe00000 which is 2MB. Since I need about 4MB of
    DMA memory, so I changed CONSISTENT_BASE to 0xffa00000,
    but I got kernel OOPS:

    kernel BUG at arch/arm/mm/consistent.c:218!
    Unable to handle kernel NULL pointer dereference at virtual address 00000000
    pgd = 67f28000
    [00000000] *pgd=07ef2031, *pte=00000000, *ppte=00000000
    Internel error: Oops: 817 [#1]


    Can anyone shed some light on me regarding this problem?
    Thanks.

  2. Re: ARM linux DMA alloc question

    On Wed, 25 Jul 2007 21:04:06 -0700, jz rearranged some electrons to form:

    > Hi,
    >
    > I am using Linux kernel 2.6.12.6 for my ARM project.
    > I use dma_alloc_writecombine() to allocate DMA uncached
    > memory. The default consistent memory is define in
    > CONSISTENT_BASE and CONSISTENT_END as 0xffc00000 and
    > 0xffe00000 which is 2MB. Since I need about 4MB of
    > DMA memory, so I changed CONSISTENT_BASE to 0xffa00000,
    > but I got kernel OOPS:
    >
    > kernel BUG at arch/arm/mm/consistent.c:218!
    > Unable to handle kernel NULL pointer dereference at virtual address 00000000
    > pgd = 67f28000
    > [00000000] *pgd=07ef2031, *pte=00000000, *ppte=00000000
    > Internel error: Oops: 817 [#1]
    >
    >
    > Can anyone shed some light on me regarding this problem?
    > Thanks.


    Looks like you have an uninitialized (zero-value) pointer that you are
    trying to use. That's what "null pointer" means.

    --
    David M (dmacchiarolo)
    http://home.triad.rr.com/redsled
    T/S 53
    sled351 Linux 2.4.18-14 has been up 2 days 8:48


  3. Re: ARM linux DMA alloc question



    David M wrote:
    > On Wed, 25 Jul 2007 21:04:06 -0700, jz rearranged some electrons to form:
    >
    >
    >>Hi,
    >>
    >>I am using Linux kernel 2.6.12.6 for my ARM project.
    >>I use dma_alloc_writecombine() to allocate DMA uncached
    >>memory. The default consistent memory is define in
    >>CONSISTENT_BASE and CONSISTENT_END as 0xffc00000 and
    >>0xffe00000 which is 2MB. Since I need about 4MB of
    >>DMA memory, so I changed CONSISTENT_BASE to 0xffa00000,
    >>but I got kernel OOPS:
    >>
    >>kernel BUG at arch/arm/mm/consistent.c:218!
    >>Unable to handle kernel NULL pointer dereference at virtual address 00000000
    >>pgd = 67f28000
    >>[00000000] *pgd=07ef2031, *pte=00000000, *ppte=00000000
    >>Internel error: Oops: 817 [#1]
    >>
    >>
    >>Can anyone shed some light on me regarding this problem?
    >>Thanks.

    >
    >
    > Looks like you have an uninitialized (zero-value) pointer that you are
    > trying to use. That's what "null pointer" means.
    >


    Hi,

    This would happen only when DMA malloc have grown over 2 MB.

    Thanks.

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