我有一台笔记本电脑 E5470，它只有 1 个 USB 控制器。我的用例是添加 USB 外部驱动器。截至目前，我能够在单个控制器上支持超过 32 个设备。
/: Bus 02.Port 1: Dev 1, Class=root_hub, Driver=xhci_hcd/10p, 5000M
|__ Port 1: Dev 8, If 0, Class=Hub, Driver=hub/4p, 5000M
|__ Port 2: Dev 10, If 0, Class=Hub, Driver=hub/4p, 5000M
|__ Port 4: Dev 26, If 0, Class=Hub, Driver=hub/4p, 5000M
|__ Port 3: Dev 35, If 0, Class=Mass Storage, Driver=usb-storage, 5000M
|__ Port 4: Dev 39, If 0, Class=Mass Storage, Driver=usb-storage, 5000M
|__ Port 2: Dev 15, If 0, Class=Hub, Driver=hub/4p, 5000M
|__ Port 4: Dev 36, If 0, Class=Mass Storage, Driver=usb-storage, 5000M
|__ Port 2: Dev 23, If 0, Class=Mass Storage, Driver=usb-storage, 5000M
|__ Port 3: Dev 29, If 0, Class=Mass Storage, Driver=usb-storage, 5000M
|__ Port 3: Dev 20, If 0, Class=Hub, Driver=hub/4p, 5000M
|__ Port 3: Dev 38, If 0, Class=Mass Storage, Driver=usb-storage, 5000M
|__ Port 1: Dev 28, If 0, Class=Mass Storage, Driver=usb-storage, 5000M
|__ Port 4: Dev 41, If 0, Class=Mass Storage, Driver=usb-storage, 5000M
|__ Port 2: Dev 34, If 0, Class=Mass Storage, Driver=usb-storage, 5000M
|__ Port 1: Dev 12, If 0, Class=Hub, Driver=hub/4p, 5000M
|__ Port 1: Dev 17, If 0, Class=Mass Storage, Driver=usb-storage, 5000M
|__ Port 4: Dev 33, If 0, Class=Mass Storage, Driver=usb-storage, 5000M
|__ Port 2: Dev 22, If 0, Class=Mass Storage, Driver=usb-storage, 5000M
|__ Port 3: Dev 27, If 0, Class=Mass Storage, Driver=usb-storage, 5000M
|__ Port 1: Dev 9, If 0, Class=Hub, Driver=hub/4p, 5000M
|__ Port 1: Dev 11, If 0, Class=Hub, Driver=hub/4p, 5000M
|__ Port 4: Dev 32, If 0, Class=Mass Storage, Driver=usb-storage, 5000M
|__ Port 2: Dev 19, If 0, Class=Mass Storage, Driver=usb-storage, 5000M
|__ Port 3: Dev 25, If 0, Class=Mass Storage, Driver=usb-storage, 5000M
|__ Port 1: Dev 14, If 0, Class=Mass Storage, Driver=usb-storage, 5000M
|__ Port 4: Dev 21, If 0, Class=Hub, Driver=hub/4p, 5000M
|__ Port 4: Dev 42, If 0, Class=Mass Storage, Driver=usb-storage, 5000M
|__ Port 2: Dev 37, If 0, Class=Mass Storage, Driver=usb-storage, 5000M
|__ Port 3: Dev 40, If 0, Class=Mass Storage, Driver=usb-storage, 5000M
|__ Port 1: Dev 30, If 0, Class=Mass Storage, Driver=usb-storage, 5000M
|__ Port 2: Dev 13, If 0, Class=Hub, Driver=hub/4p, 5000M
|__ Port 3: Dev 24, If 0, Class=Mass Storage, Driver=usb-storage, 5000M
|__ Port 4: Dev 31, If 0, Class=Mass Storage, Driver=usb-storage, 5000M
|__ Port 2: Dev 18, If 0, Class=Mass Storage, Driver=usb-storage, 5000M
|__ Port 3: Dev 16, If 0, Class=Hub, Driver=hub/4p, 5000M
|__ Port 3: Dev 50, If 0, Class=Hub, Driver=hub/4p, 5000M
|__ Port 1: Dev 51, If 0, Class=Vendor Specific Class, Driver=r8152, 5000M
|__ Port 2: Dev 52, If 0, Class=Vendor Specific Class, Driver=r8152, 5000M
|__ Port 4: Dev 53, If 0, Class=Mass Storage, Driver=uas, 5000M
现在，当我通过（更换我的 wifi 卡并放入 m2 至迷你 PCI 适配器，然后添加我自己的迷你 PCI 适配器）添加新的 USB 控制器时，它被分配到总线 4。我得到以下信息（我能够添加一些设备）
/: Bus 04.Port 1: Dev 1, Class=root_hub, Driver=xhci_hcd/2p, 5000M
|__ Port 1: Dev 2, If 0, Class=Hub, Driver=hub/4p, 5000M
|__ Port 3: Dev 6, If 0, Class=Hub, Driver=hub/4p, 5000M
|__ Port 4: Dev 19, If 0, Class=Mass Storage, Driver=uas, 5000M
|__ Port 2: Dev 13, If 0, Class=Mass Storage, Driver=uas, 5000M
|__ Port 3: Dev 17, If 0, Class=Mass Storage, Driver=uas, 5000M
|__ Port 1: Dev 10, If 0, Class=Mass Storage, Driver=usb-storage, 5000M
|__ Port 1: Dev 3, If 0, Class=Hub, Driver=hub/4p, 5000M
|__ Port 2: Dev 8, If 0, Class=Mass Storage, Driver=uas, 5000M
|__ Port 3: Dev 12, If 0, Class=Mass Storage, Driver=uas, 5000M
|__ Port 1: Dev 5, If 0, Class=Mass Storage, Driver=uas, 5000M
|__ Port 4: Dev 16, If 0, Class=Mass Storage, Driver=uas, 5000M
|__ Port 4: Dev 9, If 0, Class=Hub, Driver=hub/4p, 5000M
|__ Port 4: Dev 20, If 0, Class=Mass Storage, Driver=uas, 5000M
|__ Port 3: Dev 18, If 0, Class=Mass Storage, Driver=uas, 5000M
|__ Port 1: Dev 15, If 0, Class=Mass Storage, Driver=uas, 5000M
|__ Port 2: Dev 4, If 0, Class=Hub, Driver=hub/4p, 5000M
|__ Port 3: Dev 14, If 0, Class=Mass Storage, Driver=usb-storage, 5000M
|__ Port 1: Dev 7, If 0, Class=Mass Storage, Driver=uas, 5000M
|__ Port 2: Dev 11, If 0, Class=Mass Storage, Driver=uas, 5000M
|__ Port 2: Dev 21, If 0, Class=Hub, Driver=hub/4p, 5000M
|__ Port 1: Dev 22, If 0, Class=Hub, Driver=hub/4p, 5000M
|__ Port 4: Dev 24, If 0, Class=Mass Storage, Driver=usb-storage, 5000M
|__ Port 2: Dev 23, If 0, Class=Hub, Driver=hub/4p, 5000M
现在，当我尝试向总线 4 添加更多 USB 设备时，出现错误。我不明白.. 我的总线 2 USB 控制器比我的总线 4 有更多的设备.. 然而总线 4 抱怨它无法添加更多设备？怎么会？
我期望总线 4 能够容纳与总线 2 相同数量的设备，但它出错了
[ 733.095066] xhci_hcd 0000:01:00.0: Error while assigning device slot ID
[ 733.095081] xhci_hcd 0000:01:00.0: Max number of devices this xHCI host supports is 32.
[ 733.095092] usb 4-2.1-port3: couldn't allocate usb_device
如何找出 Unix 不允许我向控制器添加更多设备的原因？lsusb没有提供更多信息，例如特定控制器的限制是什么。
答案1
你的期望是不正确的。尽管所有 USB XHCI 控制器都提供类似的标准化编程接口，但并非所有 USB XHCI 控制器都是相同的。
在第 5.3 章中，从第 380 页开始，描述了主机控制器功能寄存器，它告诉驱动程序 XHCI 控制器的特定实现的功能是什么。 5.3.3 节描述了只读结构参数1寄存器，其中包含该特定控制器可以处理的设备插槽、中断器和端口的最大数量。
您的总线 4 控制器与总线 2 具有不同的 XHCI 硬件实现，因此它们可以处理的最大设备数量显然不同。
命令
lspci -nnvd ::0c03
应打印出足够的信息，以便您识别所使用的确切 XHCI 控制器芯片。如果您不相信我，您可以通过谷歌搜索他们的数据表来确认他们的功能。