linux-kernel - Re: [PATCH] usb: chipidea: host: Disable port power only if previously enabled

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Date:   Fri, 27 Dec 2019 09:47:25 -0500 (EST)
From:   Alan Stern <stern@...land.harvard.edu>
To:     Peter Chen <peter.chen@....com>
cc:     Guenter Roeck <linux@...ck-us.net>,
        Peter Chen <peter.chen@...escale.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Michael Grzeschik <m.grzeschik@...gutronix.de>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: Re: [PATCH] usb: chipidea: host: Disable port power only if previously
 enabled

On Fri, 27 Dec 2019, Peter Chen wrote:

> On 19-12-26 14:46:15, Alan Stern wrote:
> > On Thu, 26 Dec 2019, Guenter Roeck wrote:
> > 
> > > On shutdown, ehci_power_off() is called unconditionally to power off
> > > each port, even if it was never called to power on the port.
> > > For chipidea, this results in a call to ehci_ci_portpower() with a request
> > > to power off ports even if the port was never powered on.
> > > This results in the following warning from the regulator code.
> > 
> > That's weird -- we should always power-on every port during hub 
> > initialization.
> > 
> > It looks like there's a bug in hub.c:hub_activate(): The line under
> > HUB_INIT which calls hub_power_on() should call
> > usb_hub_set_port_power() instead.  In fact, the comment near the start
> > of hub_power_on() is wrong.  It says "Enable power on each port", but
> > in fact it only enables power for ports that had been powered-on
> > previously (i.e., the port's bit in hub->power_bits was set).  
> > Apparently this got messed up in commit ad493e5e5805 ("usb: add usb
> > port auto power off mechanism").
> > 
> > Now, the chipidea driver may still need to be updated, because 
> > ehci_turn_off_all_ports() will still be called during shutdown and it 
> > will try to power-down all ports, even those which are already powered 
> > down (for example, because the port is suspended).
> > 
> 
> Hi Alan,
> 
> When the port is suspended, why it was turned off? If it was turned
> off, how could respond wakeup event?

You're right; if a port is powered off then it can't respond to wakeup 
events.

But if the power/wakeup attribute is set to "disabled" then the port 
doesn't need to respond to wakeup events.  In that situation, usbcore 
may decide to power-down the port.

Alan Stern