<?xml version="1.0" encoding="ANSI_X3.4-1968" standalone="no"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=ANSI_X3.4-1968" /><title>Chapter 3. Memory Mapped IO</title><meta name="generator" content="DocBook XSL Stylesheets V1.75.2" /><link rel="home" href="index.html" title="Bus-Independent Device Accesses" /><link rel="up" href="index.html" title="Bus-Independent Device Accesses" /><link rel="prev" href="ch02.html" title="Chapter 2. Known Bugs And Assumptions" /><link rel="next" href="ch03s02.html" title="Accessing the device" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Chapter 3. Memory Mapped IO</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="ch02.html">Prev</a> </td><th width="60%" align="center"> </th><td width="20%" align="right"> <a accesskey="n" href="ch03s02.html">Next</a></td></tr></table><hr /></div><div class="chapter" title="Chapter 3. Memory Mapped IO"><div class="titlepage"><div><div><h2 class="title"><a id="mmio"></a>Chapter 3. Memory Mapped IO</h2></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><span class="sect1"><a href="ch03.html#getting_access_to_the_device">Getting Access to the Device</a></span></dt><dt><span class="sect1"><a href="ch03s02.html">Accessing the device</a></span></dt></dl></div><div class="sect1" title="Getting Access to the Device"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="getting_access_to_the_device"></a>Getting Access to the Device</h2></div></div></div><p>
The most widely supported form of IO is memory mapped IO.
That is, a part of the CPU's address space is interpreted
not as accesses to memory, but as accesses to a device. Some
architectures define devices to be at a fixed address, but most
have some method of discovering devices. The PCI bus walk is a
good example of such a scheme. This document does not cover how
to receive such an address, but assumes you are starting with one.
Physical addresses are of type unsigned long.
</p><p>
This address should not be used directly. Instead, to get an
address suitable for passing to the accessor functions described
below, you should call <code class="function">ioremap</code>.
An address suitable for accessing the device will be returned to you.
</p><p>
After you've finished using the device (say, in your module's
exit routine), call <code class="function">iounmap</code> in order to return
the address space to the kernel. Most architectures allocate new
address space each time you call <code class="function">ioremap</code>, and
they can run out unless you call <code class="function">iounmap</code>.
</p></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="ch02.html">Prev</a> </td><td width="20%" align="center"> </td><td width="40%" align="right"> <a accesskey="n" href="ch03s02.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Chapter 2. Known Bugs And Assumptions </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> Accessing the device</td></tr></table></div></body></html>
