Re: [rtl] contiguous shared memory

[Stuart Hughes <sehughes@zentropix.com>]

daniel sheltraw wrote:
> 
> Hello realtimers
> 
> My understanding of shared memory under RT Linux is that it uses
> vmalloc to allocate memory and therefore this memory may not be
> suitable for DMA (the memory is not guaranteed contiguous).
> 
> (1) Is this the truth, the whole truth and nothing but the truth?

Yes it is true, but I think there is a way to make it DMA safe in the
upcomming 2.4 kernels.

> (2) Is there someway to use the shared memory implementation in a
>     manner suitable for DMA?

Use the old style method of append="mem=xxxm" in your lilo.conf to
reserve some high memory and then use mmap in userland (using /dev/mem)
and ioremap in the kernel giving both the fixed address of the reserved
memory.  

Regards, Stuart