title: Kernel API to get Physical RAM Offset
body: <p>I'm writing a device driver (for Linux kernel 2.6.x) that interacts directly with physical RAM using physical addresses. For my device's memory layout (according to the output of <code>cat /proc/iomem</code>), System RAM begins at physical address <code>0x80000000</code>; however, this code may run on other devices with different memory layouts so I don't want to hard-code that offset.</p>
  
  <p>Is there a function, macro, or constant which I can use from within my device driver that gives me the physical address of the first byte of System RAM?</p>