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 10:32:20 -0400
From:   Alan Stern <stern@...land.harvard.edu>
To:     Kai-Heng Feng <kai.heng.feng@...onical.com>
Cc:     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 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?

Alan Stern