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Subject: Re: [RFC PATCH] USB:XHCI:Modify XHCI driver for USB2.0 controller
To:     Peter Chen <peter.chen@kernel.org>
CC:     Greg KH <gregkh@linuxfoundation.org>, <mathias.nyman@intel.com>,
        <linux-usb@vger.kernel.org>, <yisen.zhuang@huawei.com>,
        <linux-kernel@vger.kernel.org>
References: <1614327697-1021-1-git-send-email-liulongfang@huawei.com>
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 <87cc8b54-f530-cce0-3ea2-f879436ff5f7@huawei.com>
 <20210304013548.GA16596@nchen>
From:   liulongfang <liulongfang@huawei.com>
Message-ID: <cd4f7d23-0c21-5ea8-3224-cde1256a36a0@huawei.com>
Date:   Thu, 4 Mar 2021 12:08:43 +0800
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On 2021/3/4 9:35, Peter Chen wrote:
> On 21-02-27 11:31:00, liulongfang wrote:
>> On 2021/2/26 16:38, Greg KH 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.
>>>
>>> That sounds like a spec violation, right?  Why do you want to do this?
>>>
>>> greg k-h
>>> .
>>>
>> I hope to support a USB2.0-only mode on the XHCI controller
>> through software configuration.
>> Thanks.
> 
> If your hardware has disabled USB3 logic, when the USB3 device is plugged,
> since there are no RX signal on the bus, the device will not enable USB3
> logic, and only USB2 signals will be on the bus, there are only USB devices on
> USB2 roothub later. So, any issues you have met?
> 
I don??t want to see the USB3 bus controller in the system,
but it actually exists.
Thanks.
Longfang, Liu