PCIe驱动开发-BOIS

BIOS就接管系统控制权开始工作，它会先进行一些内存和设备的初始化工作（当然，也包括我们的PCI设备），由于商业上的原因，Phoenix等厂商的BIOS代码需要授权协议，在此，我们以另外一个款开源BIOS（openbios）为例，来剖析BIOS中，我们的PCIe设备是如何被找到以及初始化的。

PCI设备的扫描是基于深度优先搜索算法（DFS：Depth First Search)，也就是说，下级分支最多的PCI桥将最先完成其子设备的扫描。下面我们以图片来具体说明，ＢＩＯＳ是如何一步步完成PCI 设备扫描的。

第一步：

PCI Host 主桥扫描Bus 0上的设备（在一个处理器系统中，一般将与HOST主桥直接相连的PCI总线被命名为PCI Bus 0），系统首先会忽略Bus 0上的D1，D2等不会挂接PCI桥的设备，主桥发现Bridge 1后，将Bridge1 下面的PCI Bus定为 Bus 1，系统将初始化Bridge 1的配置空间，并将该桥的Primary Bus Number 和 Secondary Bus Number寄存器分别设置成0和1，以表明Bridge1 的上游总线是0，下游总线是1，由于还无法确定Bridge1下挂载设备的具体情况，系统先暂时将Subordinate Bus Number设为0xFF。如下图所示：

第二步：

系统开始扫描Bus 1，将会发现Bridge 2。系统将Bridge 2下面的PCI Bus定为Bus 2，并将该桥的Primary Bus Number 和 Secondary Bus Number寄存器分别设置成1和2，和上一步一样暂时把Bridge 2 的Subordinate Bus Number设为0xFF。如下图所示：

第三步：

系统继续扫描Bus 2，将会发现Bridge 4。系统将Bridge 4下面的PCI Bus定为Bus 3，并将该桥的Primary Bus Number 和 Secondary Bus Number寄存器分别设置成2和3，此后

系统继续扫描后发现Bus 3 下面已经没有任何Bridge了，意味着该PCI总线下已经没有任何挂载下游总线了，因此Bridge 4的Subordinate Bus Number的值已经可以确定为3了。

如下图所示：

第四步：

完成Bus 3的扫描后，系统返回到Bus 2继续扫描，发现Bus 2下面已经没有其他Bridge了。此时Bridge 2的Subordinate Bus Number的值也已经可以确定为3了。如下图所示：

第五步：

完成Bus 2的扫描后，系统返回到Bus1继续扫描，会发现Bridge 3，系统将Bridge 3下面的PCI Bus定为Bus 4。并将Bridge 4的Primary Bus Number 和 Secondary Bus Number寄存器分别设置成1和4，此后系统继续扫描后发现Bus 4 下面已经没有任何Bridge了，意味着该PCI总线下已经没有挂载任何下游总线了，因此Bridge 3 的Subordinate Bus Number的值已经可以确定为4了。如下图所示：

第六步：

完成Bus 4的扫描后，系统返回到Bus 1继续扫描， 发现Bus 1下面已经没有其他Bridge了。此时Bridge 1的Subordinate Bus Number的值已经可以确定为4，系统返回Bus 0继续扫描（Bus 0下如果有其他它Bridge，将重复上述的步骤进行扫描）。至此，本例中的整个PCI的设备扫描已经完成了。最终的设备和总线的扫描结果如下图所示。

了解了上面PCI设备扫描的大概流程，我们接下来看看Bios代码中具体是如何实现这些扫描的。

一般来说，我们可以通过两个寄存器来访问PCI的配置空间（寄存器CONFIG_ADDRESS与CONFIG_DATA），在x86体系下，这两个寄存器分别对应0xCF8和0xCFC端口，对配置空间的访问都是通过对这两个寄存器的读写来实现先。CONFIG_ADDRESS寄存器的具体位组成如下图所示：

Bus Number : 总线号（8 bit)，范围0--255。

Device Number: 设备号（5 bit)，范围0--31。

Function Number: 功能号（3 bit)，范围0--7。

Register Number: 寄存器号（6 bit),范围0--63 （配置空间一共256个字节，分割成64个4字节的寄存器，从0--63编号）。

每个PCI设备可根据上图所示的四个信息：Bus Number, Device Number, Function Number，Register Number 来进行具体设备的定位并对其配置空间访问。当我们要访问PCI设备的配置空间时，先根据以上格式设置CONFIG_ADDRESS寄存器，然后再读取CONFIG_DATA寄存器即可得到相应的配置空间寄存器的值。

因此，BIOS中PCI配置空间的读写可以封装成下面的函数：

static inline uint32_t pci_config_read32(pci_addr dev, uint8_t reg)
{
    outl(dev | reg, 0xcf8);
    return inl(0xcfc | reg);
}

static inline void pci_config_write32(pci_addr dev, uint8_t reg, uint32_t val)
{
    outl(dev | reg, 0xcf8);
    outl(val, 0xcfc);
}

static inline uint32_t pci_config_read32(pci_addr dev, uint8_t reg)
{
    outl(dev | reg, 0xcf8);
    return inl(0xcfc | reg);
}

static inline void pci_config_write32(pci_addr dev, uint8_t reg, uint32_t val)
{
    outl(dev | reg, 0xcf8);
    outl(val, 0xcfc);
}

总体来说。该BIOS扫描过程中调用如下几个主要的函数：

ob_pci_init  ----> ob_scan_pci_bus ----> pci_find_device ----> ob_pci_configure

下面我们来具体看看代码，首先BIOS执行ob_pci_init(void)函数

int ob_pci_init(void)
{
        int bus;
        unsigned long mem_base, io_base;
    char *path;

#ifdef CONFIG_DEBUG_PCI
    printk("Initializing PCI devices...\n");
#endif

    /* brute force bus scan */

    /* Find all PCI bridges */

        //获取系统指定的memeory与I/O空间的范围，分配给PCIe设备。
    mem_base = arch->mem_base;
        /* I/O ports under 0x400 are used by devices mapped at fixed
           location. */
        io_base = arch->io_base + 0x400;
    path = strdup("");

        /*遍历256条总线*/
        for (bus = 0; bus<0x100; bus++) {
        ob_scan_pci_bus(bus, &mem_base, &io_base, &path);
    }
    free(path);
    return 0;
}

int ob_pci_init(void)
{
        int bus;
        unsigned long mem_base, io_base;
    char *path;

#ifdef CONFIG_DEBUG_PCI
    printk("Initializing PCI devices...\n");
#endif

    /* brute force bus scan */

    /* Find all PCI bridges */

        //获取系统指定的memeory与I/O空间的范围，分配给PCIe设备。
    mem_base = arch->mem_base;
        /* I/O ports under 0x400 are used by devices mapped at fixed
           location. */
        io_base = arch->io_base + 0x400;
    path = strdup("");

        /*遍历256条总线*/
        for (bus = 0; bus<0x100; bus++) {
        ob_scan_pci_bus(bus, &mem_base, &io_base, &path);
    }
    free(path);
    return 0;
}

总线扫描具体实现：

static void ob_scan_pci_bus(int bus, unsigned long *mem_base,
                            unsigned long *io_base, char **path)
{
    int devnum, fn, is_multi, vid, did;
    unsigned int htype;
    pci_addr addr;
    pci_config_t config;
        const pci_dev_t *pci_dev;
    uint32_t ccode;
    uint8_t class, subclass, iface, rev;

    activate_device("/");
    for (devnum = 0; devnum < 32; devnum++) {
        is_multi = 0;
        for (fn = 0; fn==0 || (is_multi && fn<8); fn++) {
#ifdef CONFIG_XBOX
            if (pci_xbox_blacklisted (bus, devnum, fn))
                continue;
#endif
            addr = PCI_ADDR(bus, devnum, fn);       /*获取设备配置空间地址*/
            vid = pci_config_read16(addr, PCI_VENDOR_ID);  /*获取Vendor ID*/
            did = pci_config_read16(addr, PCI_DEVICE_ID);  /*获取Device ID*/

            if (vid==0xffff || vid==0)
                continue;

            ccode = pci_config_read16(addr, PCI_CLASS_DEVICE);
            class = ccode >> 8;
            subclass = ccode;
            iface = pci_config_read8(addr, PCI_CLASS_PROG);
            rev = pci_config_read8(addr, PCI_REVISION_ID);

            pci_dev = pci_find_device(class, subclass, iface,/*具体设备查找以及初始化*/
                          vid, did);

#ifdef CONFIG_DEBUG_PCI
            printk("%x:%x.%x - %x:%x - ", bus, devnum, fn,
                    vid, did);
#endif
            htype = pci_config_read8(addr, PCI_HEADER_TYPE);
            if (fn == 0)
                is_multi = htype & 0x80;

            if (pci_dev == NULL || pci_dev->name == NULL)
                            snprintf(config.path, sizeof(config.path),
                     "%s/pci%x,%x", *path, vid, did);
            else
                            snprintf(config.path, sizeof(config.path),
                     "%s/%s", *path, pci_dev->name);
#ifdef CONFIG_DEBUG_PCI
            printk("%s - ", config.path);
#endif
            config.dev = addr & 0x00FFFFFF;

            REGISTER_NAMED_NODE(ob_pci_node, config.path);

            activate_device(config.path);

                        ob_pci_configure(addr, &config, mem_base, io_base); /*配置设备的配置空间*/
            ob_pci_add_properties(addr, pci_dev, &config);

                        if (class == PCI_BASE_CLASS_BRIDGE &&
                            (subclass == PCI_SUBCLASS_BRIDGE_HOST ||
                             subclass == PCI_SUBCLASS_BRIDGE_PCI)) {
                /* host or bridge */
                free(*path);
                *path = strdup(config.path);
            }

        }
    }
    device_end();
}

static void ob_scan_pci_bus(int bus, unsigned long *mem_base,
                            unsigned long *io_base, char **path)
{
    int devnum, fn, is_multi, vid, did;
    unsigned int htype;
    pci_addr addr;
    pci_config_t config;
        const pci_dev_t *pci_dev;
    uint32_t ccode;
    uint8_t class, subclass, iface, rev;

    activate_device("/");
    for (devnum = 0; devnum < 32; devnum++) {
        is_multi = 0;
        for (fn = 0; fn==0 || (is_multi && fn<8); fn++) {
#ifdef CONFIG_XBOX
            if (pci_xbox_blacklisted (bus, devnum, fn))
                continue;
#endif
            addr = PCI_ADDR(bus, devnum, fn);       /*获取设备配置空间地址*/
            vid = pci_config_read16(addr, PCI_VENDOR_ID);  /*获取Vendor ID*/
            did = pci_config_read16(addr, PCI_DEVICE_ID);  /*获取Device ID*/

            if (vid==0xffff || vid==0)
                continue;

            ccode = pci_config_read16(addr, PCI_CLASS_DEVICE);
            class = ccode >> 8;
            subclass = ccode;
            iface = pci_config_read8(addr, PCI_CLASS_PROG);
            rev = pci_config_read8(addr, PCI_REVISION_ID);

            pci_dev = pci_find_device(class, subclass, iface,/*具体设备查找以及初始化*/
                          vid, did);

#ifdef CONFIG_DEBUG_PCI
            printk("%x:%x.%x - %x:%x - ", bus, devnum, fn,
                    vid, did);
#endif
            htype = pci_config_read8(addr, PCI_HEADER_TYPE);
            if (fn == 0)
                is_multi = htype & 0x80;

            if (pci_dev == NULL || pci_dev->name == NULL)
                            snprintf(config.path, sizeof(config.path),
                     "%s/pci%x,%x", *path, vid, did);
            else
                            snprintf(config.path, sizeof(config.path),
                     "%s/%s", *path, pci_dev->name);
#ifdef CONFIG_DEBUG_PCI
            printk("%s - ", config.path);
#endif
            config.dev = addr & 0x00FFFFFF;

            REGISTER_NAMED_NODE(ob_pci_node, config.path);

            activate_device(config.path);

                        ob_pci_configure(addr, &config, mem_base, io_base); /*配置设备的配置空间*/
            ob_pci_add_properties(addr, pci_dev, &config);

                        if (class == PCI_BASE_CLASS_BRIDGE &&
                            (subclass == PCI_SUBCLASS_BRIDGE_HOST ||
                             subclass == PCI_SUBCLASS_BRIDGE_PCI)) {
                /* host or bridge */
                free(*path);
                *path = strdup(config.path);
            }

        }
    }
    device_end();
}

具体某条总线上的设备扫描由以下函数实现：

<PRE class=cpp name="code">const pci_dev_t *pci_find_device (uint8_t class, uint8_t subclass,
                                  uint8_t iface, uint16_t vendor,
                                  uint16_t product)
{
    int (*config_cb)(const pci_config_t *config);
    const pci_class_t *pclass;
    const pci_subclass_t *psubclass;
    const pci_iface_t *piface;
    const pci_dev_t *dev;
    const void *private;
    pci_dev_t *new;
    const char *name, *type;

    name = "unknown";
    type = "unknown";
    config_cb = NULL;
    private = NULL;

    if (class == 0x00 && subclass == 0x01) {
        /* Special hack for old style VGA devices */
        class = 0x03;
        subclass = 0x00;
    } else if (class == 0xFF) {
        /* Special case for misc devices */
        dev = misc_pci;
        goto find_device;
    }
    if (class > (sizeof(pci_classes) / sizeof(pci_class_t))) {
        name = "invalid PCI device";
        type = "invalid";
        goto bad_device;
    }
    pclass = &pci_classes[class];
    name = pclass->name;
    type = pclass->type;
    for (psubclass = pclass->subc; ; psubclass++) {
        if (psubclass->subclass == 0xFF)
            goto bad_device;
        if (psubclass->subclass == subclass) {
            if (psubclass->name != NULL)
                name = psubclass->name;
            if (psubclass->type != NULL)
                type = psubclass->type;
            if (psubclass->config_cb != NULL) {
                config_cb = psubclass->config_cb;
            }
            if (psubclass->private != NULL)
                private = psubclass->private;
            if (psubclass->iface != NULL)
                break;
            dev = psubclass->devices;
            goto find_device;
        }
    }
    for (piface = psubclass->iface; ; piface++) {
        if (piface->iface == 0xFF) {
            dev = psubclass->devices;
            break;
        }
        if (piface->iface == iface) {
            if (piface->name != NULL)
                name = piface->name;
            if (piface->type != NULL)
                type = piface->type;
            if (piface->config_cb != NULL) {
                config_cb = piface->config_cb;
            }
            if (piface->private != NULL)
                private = piface->private;
            dev = piface->devices;
            break;
        }
    }
find_device:
    if (dev == NULL)
    goto bad_device;
    for (;; dev++) {
        if (dev->vendor == 0xFFFF && dev->product == 0xFFFF) {
            goto bad_device;
        }
        if (dev->vendor == vendor && dev->product == product) {
            if (dev->name != NULL)
                name = dev->name;
            if (dev->type != NULL)
                type = dev->type;
            if (dev->config_cb != NULL) {
                config_cb = dev->config_cb;
            }
            if (dev->private != NULL)
                private = dev->private;
            new = malloc(sizeof(pci_dev_t));
            if (new == NULL)
                return NULL;
            new->vendor = vendor;
            new->product = product;
            new->type = type;
            new->name = name;
            new->model = dev->model;
            new->compat = dev->compat;
            new->acells = dev->acells;
            new->scells = dev->scells;
            new->icells = dev->icells;
            new->config_cb = config_cb;
            new->private = private;

            return new;
        }
    }
bad_device:
    printk("Cannot manage '%s' PCI device type '%s':\n %x %x (%x %x %x)\n",
           name, type, vendor, product, class, subclass, iface);

    return NULL;
}



配置具体设备的配置空间

static void ob_pci_configure(pci_addr addr, pci_config_t *config, unsigned long *mem_base,
                 unsigned long *io_base)

{
    uint32_t smask, omask, amask, size, reloc, min_align;
        unsigned long base;
    pci_addr config_addr;
    int reg;
    uint8_t irq_pin, irq_line;

        /*配置中断引脚与中断编号*/
    irq_pin =  pci_config_read8(addr, PCI_INTERRUPT_PIN);
    if (irq_pin) {
        config->irq_pin = irq_pin;
        irq_pin = (((config->dev >> 11) & 0x1F) + irq_pin - 1) & 3;
        irq_line = arch->irqs[irq_pin];
        pci_config_write8(addr, PCI_INTERRUPT_LINE, irq_line);
        config->irq_line = irq_line;
    } else
        config->irq_line = -1;

        /*配置memory空间和I/O空间*/
    omask = 0x00000000;
    for (reg = 0; reg < 7; reg++) {

        config->assigned[reg] = 0x00000000;
        config->sizes[reg] = 0x00000000;

        if ((omask & 0x0000000f) == 0x4) {
            /* 64 bits memory mapping */
            continue;
        }

        if (reg == 6)
            config_addr = PCI_ROM_ADDRESS;
        else
            config_addr = PCI_BASE_ADDR_0 + reg * 4;

        config->regions[reg] = pci_config_read32(addr, config_addr);

        /* get region size */

        pci_config_write32(addr, config_addr, 0xffffffff);
        smask = pci_config_read32(addr, config_addr);
        if (smask == 0x00000000 || smask == 0xffffffff)
            continue;

        if (smask & 0x00000001 && reg != 6) {
            /* I/O space */
            base = *io_base;
            min_align = 1 << 7;
            amask = 0x00000001;
            pci_config_write16(addr, PCI_COMMAND,
                       pci_config_read16(addr,
                                 PCI_COMMAND) |
                                 PCI_COMMAND_IO);
        } else {
            /* Memory Space */
            base = *mem_base;
            min_align = 1 << 16;
            amask = 0x0000000F;
            if (reg == 6) {
                smask |= 1; /* ROM */
            }
            pci_config_write16(addr, PCI_COMMAND,
                       pci_config_read16(addr,
                                PCI_COMMAND) |
                                PCI_COMMAND_MEMORY);
        }
        omask = smask & amask;
        smask &= ~amask;
        size = (~smask) + 1;
        config->sizes[reg] = size;
        reloc = base;
        if (size < min_align)
            size = min_align;
        reloc = (reloc + size -1) & ~(size - 1);
        if (*io_base == base) {
            *io_base = reloc + size;
            reloc -= arch->io_base;
        } else {
            *mem_base = reloc + size;
        }
        pci_config_write32(addr, config_addr, reloc | omask);
        config->assigned[reg] = reloc | omask;
    }
}

通过以上这些步骤，Bios就完成了所有PCI设备的扫描，并且为每个设备分配好了系统资源。<BR>
</PRE>
<PRE></PRE>