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

Alan Stern
2025-09-12T14:29:51Z

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.

Alan Stern