From: Alan Stern <stern@rowland.harvard.edu>
To: liulongfang <liulongfang@huawei.com>
Cc: gregkh@linuxfoundation.org, mathias.nyman@intel.com,
linux-usb@vger.kernel.org, yisen.zhuang@huawei.com,
linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH] USB:XHCI:Modify XHCI driver for USB2.0 controller
Date: Sat, 27 Feb 2021 11:27:03 -0500 [thread overview]
Message-ID: <20210227162703.GA1429200@rowland.harvard.edu> (raw)
In-Reply-To: <acfdf816-e295-df1d-4039-784fb0d417c4@huawei.com>
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
next prev parent reply other threads:[~2021-02-27 16:28 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-26 8:21 Longfang Liu
2021-02-26 8:38 ` Greg KH
2021-02-27 3:31 ` liulongfang
2021-03-04 1:35 ` Peter Chen
2021-03-04 4:08 ` liulongfang
2021-02-26 9:22 ` Mathias Nyman
2021-02-27 3:34 ` liulongfang
2021-02-26 16:30 ` Alan Stern
2021-02-27 3:38 ` liulongfang
2021-02-27 3:48 ` liulongfang
2021-02-27 16:27 ` Alan Stern [this message]
2021-03-01 1:58 ` liulongfang
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