此xHCI主机支持的最大设备数为32。

Question

我有一个笔记本电脑E5470，它只有一个USB控制器。我的usecase正在添加USB外部驱动器。到目前为止，我能够在一个控制器上支持32多个设备。

/:  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，当我通过一个新的USB控制器(替换我的wifi卡，将一个m2插入到迷你PCI适配器，然后添加我自己的mini适配器)时，它被分配给总线4。

/:  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，当我试图添加更多的USB设备到总线4，我得到了错误。我不明白..。我的总线2 USB控制器比我的4总线有更多的设备。然而，总线4抱怨它不能增加更多的设备？怎么会这样?

我希望4路总线能容纳与2总线相同数量的设备，但它正在出错

[  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不会给出更多的信息，比如特定控制器的限制。

Answer 1

你的期望是错误的。并不是所有的USB控制器都是相同的，尽管它们都提供了一个相似的标准化编程接口。

您可以很容易地在互联网上找到基本的XHCI规范.

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控制器的特定实现具有哪些功能。第5.3.3小节描述了一个只读结构参数1寄存器，它包含设备插槽、中断器和这个特定控制器可以处理的端口的最大数量。

总线4控制器与总线2有不同的XHCI硬件实现，因此它们显然有不同的最大设备数量。

命令

lspci -nnvd ::0c03

应打印出足够的信息，以使您能够确定确切的XHCI控制器芯片使用。如果你不相信我的话，你可以搜索他们的数据表来确认他们的能力。