PCIE枚举过程代码实现 ----转载 学习使用

PCIe在调试过程中，经常会出现扫描不到对端EP设备的问题，在问题定位过程中，了解内核中pcie枚举流程至关重要。

PCIe枚举过程一般分为三步：
1.创建根节点
2.扫描根节点下设备
3.为根节点下设备分配资源

那么如何发现设备？
从总线扫描pcie设备的函数pci_scan_child_bus开始分析

unsigned int pci_scan_child_bus(struct pci_bus *bus)
{
unsigned int devfn, pass, max = bus->busn_res.start;
struct pci_dev *dev;

dev_dbg(&bus->dev, "scanning bus\n");

/* Go find them, Rover! */
for (devfn = 0; devfn < 0x100; devfn += 8)
    pci_scan_slot(bus, devfn);

/* Reserve buses for SR-IOV capability. */
max += pci_iov_bus_range(bus);

/*
 * After performing arch-dependent fixup of the bus, look behind
 * all PCI-to-PCI bridges on this bus.
 */
if (!bus->is_added) {
    dev_dbg(&bus->dev, "fixups for bus\n");
    pcibios_fixup_bus(bus);
    bus->is_added = 1;
}

for (pass = 0; pass < 2; pass++)
    list_for_each_entry(dev, &bus->devices, bus_list) {
        if (pci_is_bridge(dev))
            max = pci_scan_bridge(bus, dev, max, pass);
    }

/*
 * Make sure a hotplug bridge has at least the minimum requested
 * number of buses.
 */
if (bus->self && bus->self->is_hotplug_bridge && pci_hotplug_bus_size) {
    if (max - bus->busn_res.start < pci_hotplug_bus_size - 1)
        max = bus->busn_res.start + pci_hotplug_bus_size - 1;
}

/*
 * 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.
 */
dev_dbg(&bus->dev, "bus scan returning with max=%02x\n", max);
return max;

}
EXPORT_SYMBOL_GPL(pci_scan_child_bus);

该函数的核心代码为

for (devfn = 0; devfn < 0x100; devfn += 8)
pci_scan_slot(bus, devfn);

这里的bus变量来源于pci_create_root_bus,也就是创建的根总线的总线号
devfn : 设备和功能号。
这里使用的是穷举法，把所有的dev和function都尝试一次。

pci_scan_slot函数：

int pci_scan_slot(struct pci_bus *bus, int devfn)
{
unsigned fn, nr = 0;
struct pci_dev *dev;

if (only_one_child(bus) && (devfn > 0))
    return 0; /* Already scanned the entire slot */

dev = pci_scan_single_device(bus, devfn);
if (!dev)
    return 0;
if (!dev->is_added)
    nr++;

for (fn = next_fn(bus, dev, 0); fn > 0; fn = next_fn(bus, dev, fn)) {
    dev = pci_scan_single_device(bus, devfn + fn);
    if (dev) {
        if (!dev->is_added)
            nr++;
        dev->multifunction = 1;
    }
}

/* only one slot has pcie device */
if (bus->self && nr)
    pcie_aspm_init_link_state(bus->self);

return nr;

}

pci_scan_single_device：

struct pci_dev *pci_scan_single_device(struct pci_bus *bus, int devfn)
{
struct pci_dev *dev;

dev = pci_get_slot(bus, devfn);
if (dev) {
    pci_dev_put(dev);
    return dev;
}

dev = pci_scan_device(bus, devfn);
if (!dev)
    return NULL;

pci_device_add(dev, bus);

return dev;

}

核心函数为pci_scan_device:

static struct pci_dev *pci_scan_device(struct pci_bus *bus, int devfn)
{
struct pci_dev *dev;
u32 l;

if (!pci_bus_read_dev_vendor_id(bus, devfn, &l, 60*1000))
    return NULL;

dev = pci_alloc_dev(bus);
if (!dev)
    return NULL;

dev->devfn = devfn;
dev->vendor = l & 0xffff;
dev->device = (l >> 16) & 0xffff;

pci_set_of_node(dev);

if (pci_setup_device(dev)) {
    pci_bus_put(dev->bus);
    kfree(dev);
    return NULL;
}

return dev;

}

while循环里每隔一段时间就会进行一次venderid的配置读写，从上述代码中可以看出，退出循环的原因会有两个

1. config配置读写失败了 （说明链路不通）
2. 超时没有得到响应（预留时间为60s,已经非常长了，第一点失败的可能性更大）

所以扫描不到对端设备时：
1.确认建链是否成功，建链失败，肯定扫描不到对端
2.确认对端的配置空间是否可写（对端的pcie模块是否处于解复位状态）
3.确认type0,type1,iatu等参数配置是否正确，如果正确了，确认配置访问的地址空间大小是否足够。
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版权声明：本文为优快云博主「Hober_yao」的原创文章，遵循CC 4.0 BY-SA版权协议，转载请附上原文出处链接及本声明。
原文链接：https://blog.youkuaiyun.com/yhb1047818384/java/article/details/71076371