相关专题： Linux设备驱动程序开发入门
这里所说的复杂设备驱动涉及到PCI、USB、网络设备、块设备等（严格意义而言，这些设备在概念上并不并列，例如与块设备并列的是字符设备，而PCI、USB设备等都可能属于字符设备），这些设备的驱动中又涉及到一些与特定设备类型相关的较为复杂的数据结构和程序结构。本文将不对这些设备驱动的细节进行过多的介绍，仅仅进行轻描淡写的叙述。
PCI 是The Peripheral Component Interconnect -Bus的缩写，CPU使用PCI桥chipset与PCI设备通信，PCI桥chipset处理了PCI子系统与内存子系统间的所有数据交互，PCI设备完全被从内存子系统分离出来。下图呈现了PCI子系统的原理：
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| int pcidata_read_proc(char *buf, char **start, off_t offset, int len, int *eof,void *data) { int i, pos = 0; int bus, devfn; if (!pcibios_present()) return sprintf(buf, "No PCI bios present\n"); /* * This code is derived from "drivers/pci/pci.c". This means that * the GPL applies to this source file and credit is due to the * original authors (Drew Eckhardt, Frederic Potter, David * Mosberger-Tang) */ for (bus = 0; !bus; bus++) { /* only bus 0 :-) */ for (devfn = 0; devfn < 0x100 && pos < PAGE_SIZE / 2; devfn++) { struct pci_dev *dev = NULL; dev = pci_find_slot(bus, devfn); if (!dev) continue; /* Ok, we've found a device, copy its cfg space to the buffer*/ for (i = 0; i < 256; i += sizeof(u32), pos += sizeof(u32))pci_read_config_dword(dev, i, (u32*)(buf + pos)); pci_release_device(dev); /* 2.0 compatibility */ } } *eof = 1; return pos; } |
| struct pci_dev *pci_find_slot (unsigned int bus, unsigned int devfn) { struct pci_dev *pptr = kmalloc(sizeof(*pptr), GFP_KERNEL); int index = 0; unsigned short vendor; int ret; if (!pptr) return NULL; pptr->index = index; /* 0 */ ret = pcibios_read_config_word(bus, devfn, PCI_VENDOR_ID, &vendor); if (ret /* == PCIBIOS_DEVICE_NOT_FOUND or whatever error */ || vendor==0xffff || vendor==0x0000) { kfree(pptr); return NULL; } printk("ok (%i, %i %x)\n", bus, devfn, vendor); /* fill other fields */ pptr->bus = bus; pptr->devfn = devfn; pcibios_read_config_word(pptr->bus, pptr->devfn,PCI_VENDOR_ID, &pptr->vendor); pcibios_read_config_word(pptr->bus, pptr->devfn,PCI_DEVICE_ID, &pptr->device); return pptr; } |
