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

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.