Hello Prabhu, On Mon, Oct 4, 2010 at 3:55 PM, Prabhu nath <gprabhunath@xxxxxxxxx> wrote: > Dear All, > > I have an 512 MB RAM on an Intel desktop machine, of which Kernel > uses 256M for all allocation for kernel as well as for user > programs. (by passing mem=256M as a boot parameter). Hence I have > 256MB of memory which I can treat it as IO memory. > > System memory is associated from 0x00000000 - 0x20000000 (512MB) > in the physical address space. > Memory addresses from 0x00000000 - 0x10000000 (256 MB) are used by > the Kernel - memory management. Subsystem > Memory addresses from 0x10000000 - 20000000 (256MB) is used as IO > memory > > For an experiment, I used mmap() to map a page (4K) in IO memory > (page base address 0x20002000) to user virtual address This physical address is above your 512MB ram address. Arun > I used kernel function remap_pfn_range() in my kernel module's mmap > function. > > This is rightly mapping the physical page to a user virtual address. > But when I write to that address and then read. I get junk > value. > > To just verify, when I mapped the VGA controller memory to user > virtual address things are working fine. > > Can you please help me to resolve this problem. > > Regards, > Prabhu > > > -- To unsubscribe from this list: send an email with "unsubscribe kernelnewbies" to ecartis@xxxxxxxxxxxx Please read the FAQ at http://kernelnewbies.org/FAQ
