Re: [RFC PATCH] USB:XHCI:Modify XHCI driver for USB2.0 controller

liulongfang
2021-03-01T01:59:52Z

On 2021/2/28 0:27, Alan Stern Wrote:
> On Sat, Feb 27, 2021 at 11:38:08AM +0800, liulongfang wrote:
>> On 2021/2/27 0:30, Alan Stern wrote:
>>> On Fri, Feb 26, 2021 at 04:21:37PM +0800, Longfang Liu wrote:
>>>> Our current XHCI hardware controller has been customized to only
>>>> support USB 2.0 ports. When using the current xhci driver, an xhci
>>>> controller device and an ehci controller device will be created
>>>> automatically.
>>>
>>> That sentence makes no sense at all. An EHCI controller device is a
>>> piece of hardware. How can an xHCI driver, which is a piece of
>>> software, create a piece of hardware?
>>>
>>> Alan Stern
>>> .
>>>
>> The hardware device is a complete USB3.0 controller,
>> but I hope to support a USB2.0-only mode through software configuration.
>
> Even if it only supports USB-2.0 connections, an xHCI controller is
> still an xHCI controller. It doesn't magically transform into an EHCI
> controller.
>
> You are not creating an EHCI controller device. Rather, you are trying
> to restrict an xHCI controller device to make it handle only USB-2.0
> connections. If you run lsusb on a system that has an xHCI controller,
> you'll see that the controller is bound to two USB buses: a USB-2 bus
> and a USB-3 bus. But for both buses, the controller is xHCI -- not
> EHCI.
>
> Your patch description is inaccurate.
>
> Alan Stern
> .
>
Yes, you are right.
when I run lsusb on a system that has this xHCI hardware,
the system displays two USB buses: a USB-2 bus and a USB-3 bus.
Both of these are xHCI host controllers, but USB-3 bus's roothub is zero.
Thanks.
Longfang Liu.