Linux Device Drivers, Second Edition

Quick Reference

This chapter introduced the following symbols related to hardware management.

#include <linux/kernel.h> , void barrier(void)

This “software” memory barrier requests the compiler to consider all memory volatile across this instruction.

#include <asm/system.h> , void rmb(void); , void wmb(void); , void mb(void);

Hardware memory barriers. They request the CPU (and the compiler) to checkpoint all memory reads, writes, or both, across this instruction.

#include <asm/io.h> , unsigned inb(unsigned port); , void outb(unsigned char byte, unsigned port); , unsigned inw(unsigned port); , void outw(unsigned short word, unsigned port); , unsigned inl(unsigned port); , void outl(unsigned doubleword, unsigned port);

These functions are used to read and write I/O ports. They can also be called by user-space programs, provided they have the right privileges to access ports.

unsigned inb_p(unsigned port); , ...

The statement SLOW_DOWN_IO is sometimes needed to deal with slow ISA boards on the x86 platform. If a small delay is needed after an I/O operation, you can use the six pausing counterparts of the functions introduced in the previous entry; these pausing functions have names ending in _p.

void insb(unsigned port, void *addr, unsigned long count); , void outsb(unsigned port, void *addr, unsigned long count); , void insw(unsigned port, void *addr, unsigned long count); , void outsw(unsigned port, void *addr, unsigned long count); , void insl(unsigned port, void *addr, unsigned long count); , void outsl(unsigned port, void *addr, unsigned long count);

The “string functions” are optimized to transfer data from an input port to a region of memory, or the other way around. Such transfers are performed by reading or writing the same port count times.

#include <linux/ioport.h> , int check_region(unsigned long start, unsigned long len); , void request_region(unsigned long start, unsigned long len, char *name); , void release_region(unsigned long start, unsigned long len);

Resource allocators for I/O ports. The check function returns 0 for success and less than 0 in case of error.

int check_mem_region(unsigned long start, unsigned long len); , void request_mem_region(unsigned long start, unsigned long len, char *name); , void release_mem_region(unsigned long start, unsigned long len);

These functions handle resource allocation for memory regions.

#include <asm/io.h> , void *ioremap(unsigned long phys_addr, unsigned long size); , void *ioremap_nocache(unsigned long phys_addr, unsigned long size); , void iounmap(void *virt_addr);

ioremap remaps a physical address range into the processor’s virtual address space, making it available to the kernel. iounmap frees the mapping when it is no longer needed.

#include <linux/io.h> , unsigned readb(address); , unsigned readw(address); , unsigned readl(address); , void writeb(unsigned value, address); , void writew(unsigned value, address); , void writel(unsigned value, address); , memset_io(address, value, count); , memcpy_fromio(dest, source, nbytes); , memcpy_toio(dest, source, nbytes);

These functions are used to access I/O memory regions, either low ISA memory or high PCI buffers.