DMA problem - mpc8xx

Hi everybody,

I am having problems with the serial cpm driver in a mpc866. But I've f=
ound
out that my problem comes from the DMA and not really from the driver. =
 The
Rx and Tx buffers use the DMA and then the sytem hangs. However, if I s=
et
these buffers to internal ram memory (DPRAM), it works. The DMA address=
 is
configured with a kernel parameter in advance setup:
CONFIG_CONSISTENT_START (and the size in CONFIG_CONSISTENT_SIZE), but I=

don't know what they are exactly and I could not find a right documenta=
tion
about it.
I saw a pair of mailing list where some guys set the
CONFIG_CONSISTENT_START to 0xff100000, but my driver continues failing =
(and
an error about dma-mapping appears in the boot).

Did anyone have a similar problem?
Could anyone help me?

Thanks in advance,

Ra=FAl Moreno=