Subject: Re: DMA problem - mpc8xx

From: Scott Wood <[email-masked]>
Date: Tue, 23 Oct 2007 13:49:35 -0500

[email-masked] wrote:
> Hi everybody,
> 
> I am having problems with the serial cpm driver in a mpc866. But I've found
> 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 set
> 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 documentation
> 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).

What kernel version?  arch/ppc or arch/powerpc?  What is the error about 
dma-mapping that you get?  What does your memory map look like (in 
particular, is there anything that might be getting mapped in conflict 
with the consistent area at 0xff100000)?

-Scott