Re: ioremap() fails for >64 MB

On Thu, Aug 24, 2006 at 10:54:23AM +0800, alva wrote:

I think 64MB limitation of ioremap() is due to the kernel's page size.
When compiling kernel, it has an option to choose the memory page size
which is default 64MB. To use memory greater than 64MB, there is two
methods. One is to make the kernel's page size larger as Phil Nitschke
said. Another is to modify ioremap() a little bit --- just make it use
another file for "mmap" while larger than 64MB. Since the central
concept of linux is file-based, I think more files are not harmful that
only waste a little bit inode structure. And it is much more feasible
that one can choose to use file in memory or harddisk or mounted device
harddisk/memory ... ...

This is incorrect. There is no "64MB page size". Unless you are ioremapping
a region overed by a BAT/CAM, the mapping is composed of default 4KB PTEs.
The reason it fails is because of what I explained earlier. Just wanted to
clarify so nobody was confused by these statements. We can map arbitrary
sizes to the limit of what the kernel virtual address space settings
allow. This varies from platform to platform.

-Matt