应用程序中pci配置空间读写

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1. 概述

主要讲述在linux操作系统中应用程序如何读写pci配置空间。

2. 基本原理

对于pci设备，由cpu通过一个统一的入口地址向pci总桥发出命令，再由相应的pci桥间接地完成具体的读写操作。对于X86结构，pci总线的设计者在I/O地址空间保留了8个字节用于这个操作：0xcf8

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0xcff。这8个字节分成两个32位的寄存器，0xcf8是地址寄存器，0xcfc是数据寄存器。cpu先往地址寄存器中写入目标地址，然后通过数据寄存器读写数据，写入地址寄存器中的目标地址是一种包括总线号、设备号、功能号以及配置寄存器地址的综合地址。具体如下：

bit31 1

bit30-bit24 保留

bit23-bit16 总线号

bit15-bit11 设备号

bit10-bit8 功能号

bit7-bit0 寄存器地址，最低两位为0

设备的这些信息都可以通过lspci命令获取。

3. ioport读写权限

由于要通过操作ioport，所以先要获取ioport的读写权限。

能获取读写权限的函数有两个ioperm()和iopl()。

由于pci的口地址比较高，要用iopl(3)获取权限。

4. 读程序

#define

PCI_CFG_DATA 0xcfc

#define

PCI_CFG_CTRL 0xcf8

void pci_read_config_byte(unsigned char bus,

unsigned char dev, unsigned char offset, unsigned char *val)

{

unsigned

char fun = 0;

outl((0x80000000 | ((bus)<<16)

|((dev)<<11) |

((fun)<<8) | (offset

& ~0x3)), PCI_CFG_CTRL);

*val =

inl(PCI_CFG_DATA) >> ((offset

& 3) * 8);

}

void pci_read_config_word(unsigned char bus,

unsigned char dev, unsigned char offset, unsigned short *val)

{

unsigned

char fun = 0;

outl((0x80000000 | ((bus)<<16)

|((dev)<<11) |

((fun)<<8) | (offset

& ~0x3)), PCI_CFG_CTRL);

*val =

inl(PCI_CFG_DATA) >> ((offset

& 3) * 8);

}

void pci_read_config_dword(unsigned char bus,

unsigned char dev, unsigned char offset, unsigned int *val)

{

unsigned

char fun = 0;

outl((0x80000000 | ((bus)<<16)

|((dev)<<11) |

((fun)<<8) | (offset)),

PCI_CFG_CTRL);

*val =

inl(PCI_CFG_DATA);

}

很明显就是先向控制寄存器写入综合地址，格式前面已经提到，对比一下是完全一样的。然后从数据寄存器读数据即可，由于数据寄存器是32位的，如果不是读取双字，需要做移位操作。

另外一定需要注意大小端问题，如需要就要进行大小端转换，下面写程序也一样。

5. 写程序

void pci_write_config_dword(unsigned char bus,

unsigned char dev, unsigned char offset, unsigned int val)

{

unsigned

char fun = 0;

outl((0x80000000 | ((bus)<<16)

|((dev)<<11) |

((fun)<<8) | (offset)),

PCI_CFG_CTRL);

outl(val,

PCI_CFG_DATA);

}

void pci_write_config_word(unsigned char bus,

unsigned char dev, unsigned char offset, unsigned short val)

{

unsigned

long tmp;

unsigned

char fun = 0;

outl((0x80000000 | ((bus)<<16)

|((dev)<<11) |

((fun)<<8) | (offset

& ~0x3)), PCI_CFG_CTRL);

tmp =

inl(PCI_CFG_DATA);

tmp

&= ~(0xffff <<

((offset & 0x3) * 8));

tmp |= (val

<< ((offset & 0x3) *

8));

outl(tmp,

PCI_CFG_DATA);

}

void pci_write_config_byte(unsigned char bus,

unsigned char dev, unsigned char offset, unsigned short val)

{

unsigned

long tmp;

unsigned

char fun = 0;

outl((0x80000000 | ((bus)<<16)

|((dev)<<11)

|((fun)<<8) | (offset

& ~0x3)), PCI_CFG_CTRL);

tmp =

inl(PCI_CFG_DATA);

tmp

&= ~(0xff << ((offset

& 0x3) * 8));

tmp |= (val

<< ((offset & 0x3) *

8));

outl(tmp,

PCI_CFG_DATA);

}

写程序同读程序一样，先向控制寄存器写入综合地址，然后向数据寄存器写入数据。

6. 问题

上面的程序都是参考linux内核对pci空间的读写程序写的。但是在应用程序中读写pci空间和在内核中读写pci空间是完全不同的。在linux源代码中可以看到，在进行pci空间的读写操作都是在关闭中断的情况下进行的，而在用户程序空间就没有这个手段了。所以，读写可能会出错。

经过本人试验，读基本上没有出错过，而写有一定出错的概率，慎用！

有兴趣的，可以随便写个应用程序试试看。

7. 源代码

附上一份源代码，可以直接编译运行。

#include

#include

#include

static unsigned int read_pci_config_32(unsigned

char bus, unsigned char slot, unsigned char func, unsigned char

offset)

{

unsigned int v;

outl(0x80000000 |

(bus<<16) |

(slot<<11) |

(func<<8) | offset, 0xcf8);

v = inl(0xcfc);

return v;

}

unsigned char read_pci_config_8(unsigned char bus,

unsigned char slot, unsigned char func, unsigned char offset)

{

unsigned char v;

outl(0x80000000 |

(bus<<16) |

(slot<<11) |

(func<<8) | offset, 0xcf8);

v = inb(0xcfc +

(offset&3));

return v;

}

unsigned short read_pci_config_16(unsigned char

bus, unsigned char slot, unsigned char func, unsigned char

offset)

{

unsigned short v;

outl(0x80000000 |

(bus<<16) |

(slot<<11) |

(func<<8) | offset, 0xcf8);

v = inw(0xcfc +

(offset&2));

return v;

}

void write_pci_config_32(unsigned char bus,

unsigned char slot, unsigned char func, unsigned char offset,

unsigned int val)

{

outl(0x80000000 |

(bus<<16) |

(slot<<11) |

(func<<8) | offset, 0xcf8);

outl(val, 0xcfc);

}

void write_pci_config_8(unsigned char bus,unsigned

char slot, unsigned char func, unsigned char offset, unsigned char

val)

{

outl(0x80000000 |

(bus<<16) |

(slot<<11) |

(func<<8) | offset, 0xcf8);

outb(val, 0xcfc +

(offset&3));

}

void write_pci_config_16(unsigned char bus,unsigned

char slot, unsigned char func, unsigned char offset, unsigned char

val)

{

outl(0x80000000 |

(bus<<16) |

(slot<<11) |

(func<<8) | offset, 0xcf8);

outw(val, 0xcfc +

(offset&2));

}

int main(void)

{

iopl(3);

printf("0 0 0 0 = %xn", read_pci_config_16(0, 0

, 0, 0));

printf("0 0 0 2 = %xn", read_pci_config_16(0, 0

, 0, 2));

printf("0 1 0 0 = %xn",

read_pci_config_16(0, 1 , 0, 0));

printf("0 1 0 2 = %xn", read_pci_config_16(0, 1

, 0, 2));

printf("0 7 1 0 = %xn",

read_pci_config_16(0, 7 , 1, 0));

printf("0 7 1 2 = %xn", read_pci_config_16(0, 7

, 1, 2));

return 0;

}