netdev - Re: [PATCH net v1 1/1] net: usb: asix: ax88772: drop phylink use in PM to avoid MDIO runtime PM wakeups

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Message-ID: <aMQwQAaoSB0Y0-YD@shell.armlinux.org.uk>
Date: Fri, 12 Sep 2025 15:37:52 +0100
From: "Russell King (Oracle)" <linux@...linux.org.uk>
To: Alan Stern <stern@...land.harvard.edu>
Cc: Jakub Kicinski <kuba@...nel.org>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Oleksij Rempel <o.rempel@...gutronix.de>,
	Andrew Lunn <andrew+netdev@...n.ch>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>,
	Hubert Wiśniewski <hubert.wisniewski.25632@...il.com>,
	stable@...r.kernel.org, kernel@...gutronix.de,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	Lukas Wunner <lukas@...ner.de>, Xu Yang <xu.yang_2@....com>,
	linux-usb@...r.kernel.org
Subject: Re: [PATCH net v1 1/1] net: usb: asix: ax88772: drop phylink use in
 PM to avoid MDIO runtime PM wakeups

On Fri, Sep 12, 2025 at 10:29:47AM -0400, Alan Stern wrote:
> On Fri, Sep 12, 2025 at 09:33:05AM +0100, Russell King (Oracle) wrote:
> > On Thu, Sep 11, 2025 at 10:30:09PM -0400, Alan Stern wrote:
> > > The USB subsystem uses only one pair of callbacks for suspend and resume 
> > > because USB hardware has only one suspend state.  However, the callbacks 
> > > do get an extra pm_message_t parameter which they can use to distinguish 
> > > between system sleep transitions and runtime PM transitions.
> > 
> > Unfortunately, this isn't the case. While a struct usb_device_driver's
> > suspend()/resume() methods get the pm_message_t, a struct usb_driver's
> > suspend()/resume() methods do not:
> > 
> > static int usb_resume_interface(struct usb_device *udev,
> >                 struct usb_interface *intf, pm_message_t msg, int reset_resume)
> > {
> >         struct usb_driver       *driver;
> > ...
> >         if (reset_resume) {
> >                 if (driver->reset_resume) {
> >                         status = driver->reset_resume(intf);
> > ...
> >         } else {
> >                 status = driver->resume(intf);
> > 
> > vs
> > 
> > static int usb_resume_device(struct usb_device *udev, pm_message_t msg)
> > {
> >         struct usb_device_driver        *udriver;
> > ...
> >         if (status == 0 && udriver->resume)
> >                 status = udriver->resume(udev, msg);
> > 
> > and in drivers/net/usb/asix_devices.c:
> > 
> > static struct usb_driver asix_driver = {
> > ...
> >         .suspend =      asix_suspend,
> >         .resume =       asix_resume,
> >         .reset_resume = asix_resume,
> > 
> > where asix_resume() only takes one argument:
> > 
> > static int asix_resume(struct usb_interface *intf)
> > {
> 
> Your email made me go back and check the code more carefully, and it 
> turns out that we were both half-right.  :-)
> 
> The pm_message_t argument is passed to the usb_driver's ->suspend 
> callback in usb_suspend_interface(), but not to the ->resume callback in 
> usb_resume_interface().  Yes, it's inconsistent.
> 
> I suppose the API could be changed, at the cost of updating a lot of 
> drivers.  But it would be easier if this wasn't necessary, if there was 
> some way to work around the problem.  Unfortunately, I don't know 
> anything about how the network stack handles suspend and resume, or 
> what sort of locking it requires, so I can't offer any suggestions.

I, too, am unable to help further as I have no bandwidth available
to deal with this. Sorry.

-- 
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