linux-kernel - Re: [PATCH 1/2] xhci: Suspend ports to U3 directly from U1 or U2

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Date:   Wed, 10 Jun 2020 23:43:46 +0800
From:   Kai-Heng Feng <kai.heng.feng@...onical.com>
To:     Alan Stern <stern@...land.harvard.edu>
Cc:     Mathias Nyman <mathias.nyman@...el.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "open list:USB XHCI DRIVER" <linux-usb@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] xhci: Suspend ports to U3 directly from U1 or U2



> On Jun 10, 2020, at 22:32, Alan Stern <stern@...land.harvard.edu> wrote:
> 
> On Wed, Jun 10, 2020 at 02:42:30PM +0800, Kai-Heng Feng wrote:
>> xHCI spec "4.15.1 Port Suspend" states that port can be put to U3 as long
>> as Enabled bit is set and from U0, U1 or U2 state.
>> 
>> Currently only USB_PORT_FEAT_LINK_STATE puts port to U3 directly, let's
>> do the same for USB_PORT_FEAT_SUSPEND and bus suspend case.
>> 
>> This is particularly useful for USB2 devices, which may take a very long
>> time to switch USB2 LPM on and off.
> 
> Have these two patches been tested with a variety of USB-2.0 and USB-2.1 
> devices?

I tested some laptops around and they work fine.
Only internally connected USB devices like USB Bluetooth and USB Camera have USB2 LPM enabled, so this patch won't affect external connected devices.

Kai-Heng

> 
> Alan Stern