linux-kernel - Re: How the EHCI HC driver make the decision to suspend some USB devices?

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Message-ID: <Pine.LNX.4.44L0.1608191014500.12748-100000@netrider.rowland.org>
Date:   Fri, 19 Aug 2016 10:16:23 -0400 (EDT)
From:   Alan Stern <stern@...land.harvard.edu>
To:     ludeng <ludeng@...ilicon.com>
cc:     "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Lipengcheng <lpc.li@...ilicon.com>,
        "Zhangzhenxing (Christian, Device ChipSet)" 
        <zhangzhenxing@...ilicon.com>
Subject: Re: How the EHCI HC driver make the decision to suspend some USB
 devices?

On Fri, 19 Aug 2016, ludeng wrote:

> Hi,
> How the EHCI HC driver make the decision to suspend some USB devices,
> but not to suspend some others? We notice that for some USB Video
> Cameras, when they are enumerated and there is no data to transfer,
> the EHCI HC driver will suspend them by setting the Suspend bit of
> the PORTSC register. But for some other Cameras, the EHCI HC driver
> will not suspend them. The drvier make the decision based on what
> kind of information of the device ?

The EHCI driver does not make this decision.  The decision is made by 
the video camera driver and by the user.

Alan Stern