On Mon, May 4, 2009 at 1:55 PM, Judd Gilbert <ju...@tanisys.com> wrote: > I have a driver which maps some kernel allocated memory to user space which > works, and now I am trying to set that memory non-cacheable, on a power PC > using the Denx ELDK (linux-2.6.24) on a PPC460ex.
Because of the way the kernel maps main memory, you cannot do this. It is a violation of the PowerPC architecture to map a particular memory address as both cached and uncached (using different TLB entries) at the same time. When the kernel boots, it uses large mappings to map all of memory as cached. There is no mechanism to punch holes in these mappings. Therefore, if the memory is already mapped cached by the kernel, you cannot remap it as uncached. The only way around this is to use high memory, which is not mapped by the kernel normally. You can "bring in" a high memory page and map it uncached. However, I don't think there is a way for you to manually specify certain memory to be high. -- Timur Tabi Linux kernel developer at Freescale _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@ozlabs.org https://ozlabs.org/mailman/listinfo/linuxppc-dev
