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Home > Archive > Cheap Linux Hardware > July 2007 > ARM linux DMA alloc question
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ARM linux DMA alloc question
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| 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.
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| David M 2007-07-26, 7:15 am |
| 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
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David M wrote:
> On Wed, 25 Jul 2007 21:04:06 -0700, jz rearranged some electrons to form:
>
>
>
>
> 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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