On Thu, Aug 02, 2007 at 02:47:37PM +0100, Alex Gonzalez wrote: > I have a system booting the 2.6.12-rc3 32bits kernel on an RM9000 > processor and I am trying to get my head around how to access up to > 2GB of physical memory with a mem=256MB command line booting > parameter. I read that on the MIPS kernel this is split 2GB/2GB > between kernel and user space, so the kernel should be able to access > directly 2GB of physical memory. No. You assume there is nothing else in the 2GB of kernel address space. > Kernel drivers will access the memory above 256MB using ioremaps. I > need it this way as the memory above 256MB will be used in special > ways. > > What I struggle to understand is whether it would be possible to > access all the memory up to 2GB using the ioremap method. Ioremap is meant to be used for MMIO regions only. > The only way I can think of achieving this would be to use ksseg and > dynamic TLB entries to access it in 256MB chunks. The fact that I can > access ksseg must mean that the kernel is not clearing the TLB entries > that the bootloader sets up before launching the kernel, so I would > expect to be able to add/remove TLB entries dynamically without > affecting the kernel's own memory management. > > 1) Is there a simpler mechanism to achieve this? It's called 64-bit kernel. > 2) Any ill effect on the kernel from the method described above? You're basically reinventing high memory in an application optimized variant and that probably includes a similar set of problems. Ralf
