我有一台 Ubuntu 20.04 系统（Intel 2400K，ASRock Z68 Extreme3 Gen3），其中有两个90W 供电 16 端口 USB 3 集线器连接到两个USB 2主板上的端口。有 16 个外部 USB 3 驱动器连接到第一个 USB 集线器，并且很快会有 16 个外部 USB 3 驱动器连接到第二个 USB 3 集线器。
当集线器都连接到两个USB 3端口，dmesg显示日志消息
xhci_hcd 0000:07:00.0：此 xHCI 主机支持的最大设备数量为 32。
将两个集线器切换为两个USB 2端口避免了这个错误信息。
32 个设备的限制是否仍然存在？lsusb显示这些设备使用ehci而不是连接xchi？
$ lsusb -t
/: Bus 04.Port 1: Dev 1, Class=root_hub, Driver=xhci_hcd/2p, 5000M
/: Bus 03.Port 1: Dev 1, Class=root_hub, Driver=xhci_hcd/2p, 480M
/: Bus 02.Port 1: Dev 1, Class=root_hub, Driver=ehci-pci/2p, 480M
|__ Port 1: Dev 2, If 0, Class=Hub, Driver=hub/8p, 480M
|__ Port 3: Dev 98, If 0, Class=Hub, Driver=hub/4p, 480M
|__ Port 1: Dev 99, If 0, Class=Hub, Driver=hub/4p, 480M
|__ Port 3: Dev 109, If 0, Class=Mass Storage, Driver=usb-storage, 480M
|__ Port 1: Dev 101, If 0, Class=Mass Storage, Driver=usb-storage, 480M
|__ Port 4: Dev 114, If 0, Class=Mass Storage, Driver=usb-storage, 480M
|__ Port 2: Dev 104, If 0, Class=Mass Storage, Driver=usb-storage, 480M
|__ Port 2: Dev 100, If 0, Class=Hub, Driver=hub/4p, 480M
|__ Port 1: Dev 103, If 0, Class=Hub, Driver=hub/3p, 480M
|__ Port 1: Dev 108, If 0, Class=Mass Storage, Driver=uas, 480M
|__ Port 4: Dev 115, If 0, Class=Mass Storage, Driver=usb-storage, 480M
|__ Port 2: Dev 106, If 0, Class=Hub, Driver=hub/3p, 480M
|__ Port 1: Dev 112, If 0, Class=Mass Storage, Driver=uas, 480M
|__ Port 3: Dev 110, If 0, Class=Hub, Driver=hub/3p, 480M
|__ Port 1: Dev 116, If 0, Class=Mass Storage, Driver=uas, 480M
|__ Port 3: Dev 102, If 0, Class=Hub, Driver=hub/4p, 480M
|__ Port 1: Dev 107, If 0, Class=Mass Storage, Driver=usb-storage, 480M
|__ Port 2: Dev 113, If 0, Class=Mass Storage, Driver=usb-storage, 480M
|__ Port 3: Dev 118, If 0, Class=Mass Storage, Driver=usb-storage, 480M
|__ Port 4: Dev 120, If 0, Class=Mass Storage, Driver=usb-storage, 480M
|__ Port 4: Dev 105, If 0, Class=Hub, Driver=hub/4p, 480M
|__ Port 3: Dev 119, If 0, Class=Mass Storage, Driver=usb-storage, 480M
|__ Port 1: Dev 111, If 0, Class=Mass Storage, Driver=usb-storage, 480M
|__ Port 4: Dev 121, If 0, Class=Mass Storage, Driver=usb-storage, 480M
|__ Port 2: Dev 117, If 0, Class=Mass Storage, Driver=usb-storage, 480M
|__ Port 4: Dev 65, If 0, Class=Hub, Driver=hub/4p, 480M
|__ Port 3: Dev 69, If 0, Class=Hub, Driver=hub/4p, 480M
|__ Port 1: Dev 66, If 0, Class=Hub, Driver=hub/4p, 480M
|__ Port 3: Dev 97, If 0, Class=Mass Storage, Driver=usb-storage, 480M
|__ Port 4: Dev 96, If 0, Class=Mass Storage, Driver=usb-storage, 480M
|__ Port 4: Dev 71, If 0, Class=Hub, Driver=hub/4p, 480M
|__ Port 2: Dev 67, If 0, Class=Hub, Driver=hub/4p, 480M
/: Bus 01.Port 1: Dev 1, Class=root_hub, Driver=ehci-pci/2p, 480M
|__ Port 1: Dev 2, If 0, Class=Hub, Driver=hub/6p, 480M
|__ Port 2: Dev 3, If 0, Class=Human Interface Device, Driver=usbhid, 12M