On Fri, Sep 12, 2025 at 03:37:52PM +0100, Russell King (Oracle) wrote:
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.
Thanks for all the valuable input.
I’ll process the feedback and investigate possible ways to proceed. As a first step I’ll measure the actual power savings from USB auto-suspend on AX88772 to see if runtime PM is worth the added complexity.
Best Regards, Oleksij