DMA Crash on MPC8272

I am writing a Linux network device driver using Linux 2.4 with an
MPC8272 processor. I allocate buffers using kmalloc with the GFP_DMA
and GFP_KERNEL flags set. I DMA using these buffers to and from the
memory of a PCI device that is not a bus master. When I DMA from the
buffers to the PCI device, it does not crash, but when I DMA from the
PCI device to the buffers, the system crashes, sometimes immediately
and sometimes in as much as a half hour.

What could cause this difference in behavior based on the direction of
the DMA?

Hiya Bill,

> [...] When I DMA from the
> buffers to the PCI device, it does not crash, but when I DMA from the
> PCI device to the buffers, the system crashes, sometimes immediately
> and sometimes in as much as a half hour.
>
> What could cause this difference in behavior based on the direction of
> the DMA?

The last time something like this happened to me, it was because the
memory destination was wrong and I was overwriting part of the kernel.

Sounds like pretty similar behaviour.

Cheers,
John McCallum
Edinburgh