PCI总线---PCI设备扫描过程

8.2PCI设备扫描过程

Linux内核具备多种PCI的扫描方式，它们之间大同小异。

本节使用传统的扫描方式 执行pci_legacy_init函数，定义在legacy.c文件中 ：

static int __init pci_legacy_init(void){if (!raw_pci_ops) {printk("PCI: System does not support PCI\n");return 0;}if (pcibios_scanned++)return 0;printk("PCI: Probing PCI hardware\n");pci_root_bus = pcibios_scan_root(0);if (pci_root_bus)pci_bus_add_devices(pci_root_bus);pcibios_fixup_peer_bridges();return 0;}

pci_legacy_init函数

首先--扫描0号总线，扫描成功，则把0号总线作为系统的根总线

pci_root_bus = pcibios_scan_root(0);

然后--把0号总线扫描到的设备加入到一个全局的PCI设备链表

最后--调用pcibios_fixup_peer_bridges对BIOS提供的PCI总线进行进一步的扫描

/** Discover remaining PCI buses in case there are peer host bridges.* We use the number of last PCI bus provided by the PCI BIOS.*/static void __devinit pcibios_fixup_peer_bridges(void){int n, devfn;if (pcibios_last_bus <= 0 || pcibios_last_bus >= 0xff)return;DBG("PCI: Peer bridge fixup\n");for (n=0; n <= pcibios_last_bus; n++) {u32 l;if (pci_find_bus(0, n))continue;for (devfn = 0; devfn < 256; devfn += 8) {if (!raw_pci_ops->read(0, n, devfn, PCI_VENDOR_ID, 2, &l) &&l != 0x0000 && l != 0xffff) {DBG("Found device at %02x:%02x [%04x]\n", n, devfn, l);printk(KERN_INFO "PCI: Discovered peer bus %02x\n", n);pci_scan_bus(n, &pci_root_ops, NULL);break;}}}}

啊

啊

啊

8.2.1扫描0号总线

扫描 0号总线调用的是pcibios_scan_root函数，代码如下：

struct pci_bus * __devinit pcibios_scan_root(int busnum){struct pci_bus *bus = NULL;dmi_check_system(pciprobe_dmi_table);while ((bus = pci_find_next_bus(bus)) != NULL) {if (bus->number == busnum) {/* Already scanned */return bus;}}printk(KERN_DEBUG "PCI: Probing PCI hardware (bus %02x)\n", busnum);return pci_scan_bus_parented(NULL, busnum, &pci_root_ops, NULL);}

首先遍历所有的PCI总线，检查指定的总线是否已经扫描过，如果已经扫描，则直接返回。如果尚未扫描，则调用pci_bus_parented函数扫描总线。

啊

啊

啊

啊

8.2.1扫描总线上的PCI设备

pci_bus_parented函数的功能是扫描总线上可能接入的256个PCI设备，如果扫描到的PCI设备是桥设备，还要递归扫描桥设备，把桥设备可能接入的PCI设备扫描出来，代码清单如下：

struct pci_bus * __devinit pci_scan_bus_parented(struct device *parent,int bus, struct pci_ops *ops, void *sysdata){struct pci_bus *b;b = pci_create_bus(parent, bus, ops, sysdata);if (b)b->subordinate = pci_scan_child_bus(b);return b;}

pci_scan_bus_parented函数可分成两个步骤：

第一步：创建一个总线对象

第二步：调用pci_scan_child_bus对创建的总线对象进行递归扫描

1、创建一个总线对象

pci_create_bus函数，parent参数为空NULL，说明这条总线没有父设备，是一条根总线

1）pci_create_bus第一部分是创建一个总线对象和一个设备对象，代码如下：

struct pci_bus * __devinit pci_create_bus(struct device *parent,int bus, struct pci_ops *ops, void *sysdata){int error;struct pci_bus *b;struct device *dev;b = pci_alloc_bus();if (!b)return NULL;//--申请一个dev结构 --dev = kmalloc(sizeof(*dev), GFP_KERNEL);if (!dev){kfree(b);return NULL;}b->sysdata = sysdata;b->ops = ops;//--检查是否被创建if (pci_find_bus(pci_domain_nr(b), bus)) {/* If we already got to this bus through a different bridge, ignore it */pr_debug("PCI: Bus %04x:%02x already known\n", pci_domain_nr(b), bus);goto err_out;}//--创建总线加入PCI总线链表down_write(&pci_bus_sem);list_add_tail(&b->node, &pci_root_buses);up_write(&pci_bus_sem);

PCI总线本身是一个设备，所以除了总线对象外，还要为它创建一个设备对象。总线对象是链接到一个全局的链表头pci_root_buses，这样通过这条链表，可以遍历所有的PCI总线。

2）pci_create_bus函数第二部分执行结构和对象的注册

//设置Dev结构并登记到系统memset(dev, 0, sizeof(*dev));dev->parent = parent;dev->release = pci_release_bus_bridge_dev;sprintf(dev->bus_id, "pci%04x:%02x", pci_domain_nr(b), bus);error = device_register(dev);if (error)goto dev_reg_err;b->bridge = get_device(dev);b->class_dev.class = &pcibus_class;sprintf(b->class_dev.class_id, "%04x:%02x", pci_domain_nr(b), bus);error = class_device_register(&b->class_dev);if (error)goto class_dev_reg_err;error = class_device_create_file(&b->class_dev, &class_device_attr_cpuaffinity);if (error)goto class_dev_create_file_err;/* Create legacy_io and legacy_mem files for this bus */pci_create_legacy_files(b);error = sysfs_create_link(&b->class_dev.kobj, &b->bridge->kobj, "bridge");if (error)goto sys_create_link_err;b->number = b->secondary = bus;

首先把设备对象注册到系统，这个过程6章已经分析过了。其次四注册PCI总线类和sysfs文件系统创建符号链接

3）pci_create_bus函数最后设置PCI总线的资源

b->resource[0] = &ioport_resource;b->resource[1] = &iomem_resource;return b;

PCI总线资源有两类，

一类是：I/O端口；

另一类：I/O内存；

总线上所有设备的端口和内存组成一个空间，为了避免冲突，内存设置了全局的数据结构ioport_resoure和iomem_resource，分别保存所有的I/O端口资源和所有的I/O内存资源 。

2、扫描总线

现在返回pci_scan_bus_parented函数，当成功创建总线对象后，开始扫描这条总线，调用pci_scan_child_bus

unsigned int __devinit pci_scan_child_bus(struct pci_bus *bus){unsigned int devfn, pass, max = bus->secondary;struct pci_dev *dev;pr_debug("PCI: Scanning bus %04x:%02x\n", pci_domain_nr(bus), bus->number);/* Go find them, Rover! *///--扫描总线下面的256个设备for (devfn = 0; devfn < 0x100; devfn += 8)pci_scan_slot(bus, devfn);/** After performing arch-dependent fixup of the bus, look behind* all PCI-to-PCI bridges on this bus.*/pr_debug("PCI: Fixups for bus %04x:%02x\n", pci_domain_nr(bus), bus->number);pcibios_fixup_bus(bus);/* 扫描子总线，分两次扫描，第一次扫描BIOS发现的总线 */for (pass=0; pass < 2; pass++)list_for_each_entry(dev, &bus->devices, bus_list) {if (dev->hdr_type == PCI_HEADER_TYPE_BRIDGE ||dev->hdr_type == PCI_HEADER_TYPE_CARDBUS)max = pci_scan_bridge(bus, dev, max, pass);}/** We've scanned the bus and so we know all about what's on* the other side of any bridges that may be on this bus plus* any devices.** Return how far we've got finding sub-buses.*/pr_debug("PCI: Bus scan for %04x:%02x returning with max=%02x\n",pci_domain_nr(bus), bus->number, max);return max;}

扫描PCI总线试过递归过程。每条PCI总线可以配置32个多功能设备，每个多功能设备又可以安装8个子设备，总共就是256个设备。这256个设备中，有的设备可能是PCI桥，每个PCI桥下面又可以介入256设备。通过函数pci_scan_slot扫描每个多功能设备的8个子设备，通过pci_scan_bridge函数扫描PCI桥设备。对于桥设备，还要递归调用spi_scan_child_bus函数扫描本桥设备下面可能接入的PCI设备。

啊

8.2.3扫描多功能设备

扫描PCI 多功能设备和扫描 桥设备有重复的地方，因此本节以扫描多功能设备的函数pci_scan_slot为例进行分析，代码如下：

/*** pci_scan_slot - scan a PCI slot on a bus for devices.* @bus: PCI bus to scan* @devfn: slot number to scan (must have zero function.)** Scan a PCI slot on the specified PCI bus for devices, adding* discovered devices to the @bus->devices list. New devices* will have an empty dev->global_list head.*/int __devinit pci_scan_slot(struct pci_bus *bus, int devfn){int func, nr = 0;int scan_all_fns;scan_all_fns = pcibios_scan_all_fns(bus, devfn);for (func = 0; func < 8; func++, devfn++) {struct pci_dev *dev;dev = pci_scan_single_device(bus, devfn);if (dev) {nr++;/** If this is a single function device,* don't scan past the first function.*/if (!dev->multifunction) {if (func > 0) {dev->multifunction = 1;} else {break;}}} else {if (func == 0 && !scan_all_fns)break;}}return nr;}

pci_scan_slot函数从 0号设备开始进行扫描，如果发现是单功能设备，不再继续扫描，如果发现是多功能设备，则进行8次扫描。

8.2.4扫描单个设备

扫描单个设备调用pci_scan_single_device函数，输入参数是总线结构和设备功能号，代码:

pci_scan_single_device(struct pci_bus *bus, int devfn){struct pci_dev *dev;dev = pci_scan_device(bus, devfn);if (!dev)return NULL;pci_device_add(dev, bus);pci_scan_msi_device(dev);return dev;}

pci_scan_single_device函数调用pci_scan_device扫描设备，扫描成功后把设备加入总线的设备链表。最后的pci_scan_msi_device函数是检查设备的MSI能力，MSI和设备的中断有关。

啊

8.2.5扫描设备信息

扫描PCI设备通过读取PCI设备的配置空间完成，这部分原理在第3章介绍过。扫描设备的代码pci_scan_device函数：

pci_scan_device(struct pci_bus *bus, int devfn){struct pci_dev *dev;u32 l;u8 hdr_type;int delay = 1;//--读PCI设备制造商的ID--if (pci_bus_read_config_dword(bus, devfn, PCI_VENDOR_ID, &l))return NULL;/* some broken boards return 0 or ~0 if a slot is empty: */if (l == 0xffffffff || l == 0x00000000 ||l == 0x0000ffff || l == 0xffff0000)return NULL;/* Configuration request Retry Status *//** --处理需要重复读配置信息的情况-- **/while (l == 0xffff0001) {msleep(delay);delay *= 2;if (pci_bus_read_config_dword(bus, devfn, PCI_VENDOR_ID, &l))return NULL;/* Card hasn't responded in 60 seconds? Must be stuck. */if (delay > 60 * 1000) {printk(KERN_WARNING "Device %04x:%02x:%02x.%d not ""responding\n", pci_domain_nr(bus),bus->number, PCI_SLOT(devfn),PCI_FUNC(devfn));return NULL;}}

pci_scan_device函数第一部分读PCI设备制造商的ID，所有制造商都要分配厂商的ID号，从ID号就可以获得设备厂商信息。

这部分代码要处理异常情况，某些设备可能返回重试状态，这种情况要延迟一段时间，再次尝试读制造商的ID，如果延迟时间超过60秒，还没有读到ID，则返回失败。

----pci_scan_device函数第二部分为设备分配一个PCI设备结构，然后根据设备配置空间读取的信息对设备进行赋值

/*** --- 读PCI设备的类型 --- ***/if (pci_bus_read_config_byte(bus, devfn, PCI_HEADER_TYPE, &hdr_type))return NULL;/*** --- 申请一个PCI设备结构 --- ***/dev = kzalloc(sizeof(struct pci_dev), GFP_KERNEL);if (!dev)return NULL;/*** --- 设置PCI设备的参数，包括类型、制造商、是否多功能 --- ***/dev->bus = bus;dev->sysdata = bus->sysdata;dev->dev.parent = bus->bridge;dev->dev.bus = &pci_bus_type;dev->devfn = devfn;dev->hdr_type = hdr_type & 0x7f;dev->multifunction = !!(hdr_type & 0x80);dev->vendor = l & 0xffff;dev->device = (l >> 16) & 0xffff;dev->cfg_size = pci_cfg_space_size(dev);dev->error_state = pci_channel_io_normal;/* Assume 32-bit PCI; let 64-bit PCI cards (which are far rarer)set this higher, assuming the system even supports it. *//*** --- 设置设备的dma 地址掩码 --- ***/dev->dma_mask = 0xffffffff;if (pci_setup_device(dev) < 0) {kfree(dev);return NULL;}return dev;}

此时，只读取配置空间的制造商ID和头部信息（HEADER_TYPE），信息的进一步读取在函数pci_setup_device中完成，这个函数同时设置PCI设备的信息：

/*** pci_setup_device - fill in class and map information of a device* @dev: the device structure to fill** Initialize the device structure with information about the device's * vendor,class,memory and IO-space addresses,IRQ lines etc.* Called at initialisation of the PCI subsystem and by CardBus services.* Returns 0 on success and -1 if unknown type of device (not normal, bridge* or CardBus).*/static int pci_setup_device(struct pci_dev * dev){u32 class;sprintf(pci_name(dev), "%04x:%02x:%02x.%d", pci_domain_nr(dev->bus),dev->bus->number, PCI_SLOT(dev->devfn), PCI_FUNC(dev->devfn));/*** -- 读类别 -- ***/pci_read_config_dword(dev, PCI_CLASS_REVISION, &class);class >>= 8; /* upper 3 bytes */dev->class = class;class >>= 8;pr_debug("PCI: Found %s [%04x/%04x] %06x %02x\n", pci_name(dev),dev->vendor, dev->device, class, dev->hdr_type);/* "Unknown power state" */dev->current_state = PCI_UNKNOWN;/* Early fixups, before probing the BARs */pci_fixup_device(pci_fixup_early, dev);class = dev->class >> 8;

pci_setup_device函数第一部分是读设备类的信息：

------高24位：class信息

------低8位 ：revision信息，并根据读取的信息设置PCI设备

pci_setup_device函数第二部分根据设备类型读需要的信息

switch (dev->hdr_type) { /* header type */case PCI_HEADER_TYPE_NORMAL: /* standard header */if (class == PCI_CLASS_BRIDGE_PCI)goto bad;/*** ------ 读中断信息 ------ ***/pci_read_irq(dev);/*** ------ 读配置空间的资源信息 6条信息 ------ ***/pci_read_bases(dev, 6, PCI_ROM_ADDRESS);/*** ------ 读子系统厂商的ID ------ ***/pci_read_config_word(dev, PCI_SUBSYSTEM_VENDOR_ID, &dev->subsystem_vendor);/*** ------ 读子系统的ID ------ ***/pci_read_config_word(dev, PCI_SUBSYSTEM_ID, &dev->subsystem_device);break;case PCI_HEADER_TYPE_BRIDGE: /* bridge header */if (class != PCI_CLASS_BRIDGE_PCI)goto bad;/* The PCI-to-PCI bridge spec requires that subtractivedecoding (i.e. transparent) bridge must have programminginterface code of 0x01. */ pci_read_irq(dev);dev->transparent = ((dev->class & 0xff) == 1);pci_read_bases(dev, 2, PCI_ROM_ADDRESS1);break;case PCI_HEADER_TYPE_CARDBUS: /* CardBus bridge header */if (class != PCI_CLASS_BRIDGE_CARDBUS)goto bad;pci_read_irq(dev);pci_read_bases(dev, 1, 0);pci_read_config_word(dev, PCI_CB_SUBSYSTEM_VENDOR_ID, &dev->subsystem_vendor);pci_read_config_word(dev, PCI_CB_SUBSYSTEM_ID, &dev->subsystem_device);break;default: /* unknown header */printk(KERN_ERR "PCI: device %s has unknown header type %02x, ignoring.\n",pci_name(dev), dev->hdr_type);return -1;bad:printk(KERN_ERR "PCI: %s: class %x doesn't match header type %02x. Ignoring class.\n",pci_name(dev), class, dev->hdr_type);dev->class = PCI_CLASS_NOT_DEFINED;}/* We found a fine healthy device, go go go... */return 0;}

设备有三种类型：通常的PCI设备、PCI桥设备和CARDBUS设备。

每种设备都要读中断信息和资源信息。PCI设备的配置空间提供两种资源，一种是I/O端口，另一种是I/O内存。

普通设备可以提供6个资源信息，桥设备只有2个资源信息。

普通操作系统扫描PCI总线，目的是获得PCI设备的信息，然后为每个设备分配一个PCI设备结构。PCI总线扫描到设备之后，需要设备加载正确的驱动，这部分在67章中。

补充：

内核启动PCI总线枚举的过程中，跟踪到底层扫描总线上每个设备，都是通过每个设备的vendorID来确定设备的有无，函数pci_bus_read_config_dword没有找到实现，只是找到了EXPORT_SYMBOL(pci_bus_read_config_dword)。

access.c中

#define PCI_OP_WRITE(size,type,len) \int pci_bus_write_config_##size \(struct pci_bus *bus, unsigned int devfn, int pos, type value)\{\int res;\unsigned long flags;\if (PCI_##size##_BAD) return PCIBIOS_BAD_REGISTER_NUMBER;\spin_lock_irqsave(&pci_lock, flags);\res = bus->ops->write(bus, devfn, pos, len, value);\spin_unlock_irqrestore(&pci_lock, flags);\return res;\}

PCI_OP_READ(byte, u8, 1)

PCI_OP_READ(word, u16, 2)

PCI_OP_READ(dword, u32, 4)

PCI_OP_WRITE(byte, u8, 1)

PCI_OP_WRITE(word, u16, 2)

PCI_OP_WRITE(dword, u32, 4)

EXPORT_SYMBOL(pci_bus_read_config_byte);

EXPORT_SYMBOL(pci_bus_read_config_word);

EXPORT_SYMBOL(pci_bus_read_config_dword);

EXPORT_SYMBOL(pci_bus_write_config_byte);

EXPORT_SYMBOL(pci_bus_write_config_word);

EXPORT_SYMBOL(pci_bus_write_config_dword);

------看PCI_OP_READ宏定义，##是宏定义中用来字符串替换的，也就是将宏定义穿进来的参数字符串原封不动替换

这样也就有了函数pci_bus_read_config_byte/word/dword等

啊

啊

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