Accessing hardware I/O memory from the kernel

An interesting issue that you, as a device driver author, will likely face is this: you need to be able to access and work on the I/O memory, the hardware registers, and/or hardware memory of a peripheral chip. This is, in fact, typically the way in which the driver programs the hardware at the level of the "metal": by issuing commands to it via its registers and/or peripheral memory. However, there is an issue to be faced with directly accessing hardware I/O memory on Linux. In this first section, we'll take a look at this issue and provide a solution for it.