作者：曹忠明,华清远见嵌入式学院讲师。

PCI是外围设备互联的简称(Peripheral Component Interconnect)的简称，作为一种通用的总线接口标准，他在计算机系统中得到了广泛的使用。PCI的速度能够达到132M/s。在这里简单的介绍一下 linux 下PCI驱动的实现。

在编写一个PCI驱动的时候我们先得确定系统中是否有我们的设备。我们可以通过lspci查看PCI设备。

[root@localhost ~]# lspci

00:00.0 Host bridge: Intel Corporation 440BX/ZX/DX - 82443BX/ZX/DX Host bridge (rev 01)

00:01.0 PCI bridge: Intel Corporation 440BX/ZX/DX - 82443BX/ZX/DX AGP bridge (rev 01)

00:07.0 ISA bridge: Intel Corporation 82371AB/EB/MB PIIX4 ISA (rev 08)

00:07.1 IDE interface: Intel Corporation 82371AB/EB/MB PIIX4 IDE (rev 01)

00:07.2 USB Controller: Intel Corporation 82371AB/EB/MB PIIX4 USB

00:07.3 Bridge: Intel Corporation 82371AB/EB/MB PIIX4 ACPI (rev 08)

00:0f.0 VGA compatible controller: VMware Inc Abstract SVGA II Adapter

00:10.0 SCSI storage controller: LSI Logic / Symbios Logic 53c1030 PCI-X Fusion-MPT Dual Ultra320 SCSI (rev 01)

00:11.0 PCI bridge: VMware Inc PCI bridge (rev 02)

02:00.0 Ethernet controller: Advanced Micro Devices [AMD] 79c970 [PCnet32 LANCE] (rev 10)

02:01.0 Multimedia audio controller: Ensoniq ES1371 [AudioPCI-97] (rev 02)

02:02.0 USB Controller: VMware Inc Abstract USB2 EHCI Controller

确定有设备以后，我们就可以开始我们的PCI设备驱动的编写了。

1、 首先我们介绍几个必须了解的结构体

pci_driver：这个结构体定义在include/linux/pci.h,这里我们最关注的是id_table、probe和remove。id_table是一个结构体数组，用来存放驱动程序适用的设备信息，probe用于检测设备，remove为设备卸载时调用。

struct pci_driver {

struct list_head node;

char *nAME;

const struct pci_device_id *id_table; /* must be non-NULL for probe to be called */

int (*probe) (struct pci_dev *dev, const struct pci_device_id *id); /* New device inserted */

void (*remove) (struct pci_dev *dev); /* Device removed (NULL if not a hot-plug capable driver) */

int (*suspend) (struct pci_dev *dev, pm_message_t state); /* Device suspended */

int (*resume) (struct pci_dev *dev); /* Device woken up */

int (*enable_wake) (struct pci_dev *dev, pci_power_t state, int enable); /* Enable wake event */

void (*shutdown) (struct pci_dev *dev);

struct pci_error_handlers *err_handler;

struct device_driver driver;

struct pci_dynids dynids;

};

pci_dev:这个结构体同样也是定义在include/linux/pci.h,它详细的定义了PCI的设备的信息。这些信息我们可以通过查看proc及sys目录先相应文件得到。

struct pci_dev {

struct list_head global_list; /* node in list of all PCI devices */

struct list_head bus_list; /* node in per-bus list */

struct pci_bus *bus; /* bus this device is on */

struct pci_bus *subordinate; /* bus this device bridges to */

void *sysdata; /* hook for sys-specific extension */

struct proc_dir_entry *procent; /* device entry in /proc/bus/pci */

unsigned int devfn; /* encoded device & function index */

unsigned short vendor;

unsigned short device;

unsigned short subsystem_vendor;

unsigned short subsystem_device;

unsigned int class; /* 3 bytes: (base,sub,prog-if) */

u8 hdr_type; /* PCI header type (`multi" flag masked out) */

u8 rom_base_reg; /* which config register controls the ROM */

u8 pin; /* which interrupt pin this device uses */

struct pci_driver *driver; /* which driver has allocated this device */

u64 dma_mask; /* Mask of the bits of bus address this

device implements. Normally this is

0xffffffff. You only need to change

this if your device has broken DMA

or supports 64-bit transfers. */

pci_power_t current_state; /* Current operating state. In ACPI-speak,

this is D0-D3, D0 being fully functional,

and D3 being off. */

pci_channel_state_t error_state; /* current connectivity state */

struct device dev; /* Generic device interface */

/* device is compatible with these IDs */

unsigned short vendor_compatible[DEVICE_COUNT_COMPATIBLE];

unsigned short device_compatible[DEVICE_COUNT_COMPATIBLE];

int cfg_size; /* Size of configuration space */

/*

* Instead of touching interrupt line and base address registers

* directly, use the values stored here. They might be different!

*/

unsigned int irq;

struct resource resource[DEVICE_COUNT_RESOURCE]; /* I/O and memory regions + expansion ROMs */

/* These fields are used by common fixups */

unsigned int transparent:1; /* Transparent PCI bridge */

unsigned int multifunction:1; /* Part of multi-function device */

/* keep track of device state */

unsigned int is_enabled:1; /* pci_enable_device has been called */

unsigned int is_busmaster:1; /* device is busmaster */

unsigned int no_msi:1; /* device may not use msi */

unsigned int no_d1d2:1; /* only allow d0 or d3 */

unsigned int block_ucfg_access:1; /* userspace config space access is blocked */

unsigned int broken_parity_status:1; /* Device generates false positive parity */

unsigned int msi_enabled:1;

unsigned int msix_enabled:1;

#ifndef __GENKSYMS__

unsigned int is_managed:1;

#endif

u32 saved_config_space[16]; /* config space saved at suspend time */

struct hlist_head saved_cap_space;

struct bin_attribute *rom_attr; /* attribute descriptor for sysfs ROM entry */

int rom_attr_enabled; /* has display of the rom attribute been enabled? */

struct bin_attribute *res_attr[DEVICE_COUNT_RESOURCE]; /* sysfs file for resources */

#ifndef __GENKSYMS__

u8 revision; /* PCI revision, low byte of class word */

#endif

};

2、 这里我们开始编写一个简单的PCI驱动

● LICENSE的声明必不可少：

MODULE_LICENSE ("GPL");

● pci_driver的定义：

#define PCI_MODULE_NAME "dsp_pci_module"

static struct pci_driver new_pci_driver = {

name: PCI_MODULE_NAME,

id_table:new_pci_tbl,

probe: pci_probe,

remove: pci_remove,

};

pci_driver中对应的pci_tbl定义：

#define NEW_PCI_VENDOR_ID 0x15ad

#define NEW_PCI_DEVICE_ID 0x0405

static struct pci_device_id new_pci_tbl[] __initdata = {

{NEW_PCI_VENDOR_ID, NEW_PCI_DEVICE_ID,

PCI_ANY_ID, PCI_ANY_ID, 0, 0, 0},

{0,}

};

MODULE_DEVICE_TABLE (pci, new_pci_tbl);

● probe函数的声明：

static int __devinit pci_probe(struct pci_dev *pci_dev, const struct pci_device_id *pci_id)

{

/*在这里我们可以对PCI设备进行初始化及IO的注册等操作*/

return 0;

}

● remove函数的声明:

static void __devexit pci_remove(struct pci_dev *pci_dev)

{

/*对资源释放*/

}

● module_init和module_exit这两个函数在驱动中必不可少，分别在驱动被加载和卸载时调用：

static int __init pci_init_module (void)

{

return pci_register_driver(&new_pci_driver);

}

static void __exit pci_cleanup_module (void)

{

pci_unregister_driver(&new_pci_driver);

}

module_init (pci_init_module);

module_exit (pci_cleanup_module);

下面我们说一下这个驱动的执行过程：

系统加载模块是调用pci_init_module函数，在这个函数中我们通过pci_register_driver把new_pci_driver注册到系统中，这个函数首先检测id_table中定义的PCI信息是否和系统中的PCI信息有匹配，如果有则返回0，匹配成功后调用probe函数对PCI设备进行进一步的操作。同样在卸载模块时调用pci_cleanup_module，这个函数中通过pci_unregister_driver对new_pci_driver进行注销，这个会调用到remove函数。

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