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

Russell King (Oracle)
2025-09-11T20:46:50Z

On Thu, Sep 11, 2025 at 07:55:13AM -0700, Jakub Kicinski wrote:
> On Thu, 11 Sep 2025 15:39:20 +0100 Russell King (Oracle) wrote:
> > I'm not surprised. I'm guessing phylib is using polled mode, and
> > removing the suspend/resume handling likely means that it's at the
> > mercy of the timings of the phylib state machine running (which is
> > what is complaining here) vs the MDIO bus being available for use.
> >
> > Given that this happens, I'm convinced that the original patch is
> > the wrong approach. The driver needs the phylink suspend/resume
> > calls to shutdown and restart phylib polling, and the resume call
> > needs to be placed in such a location that the MDIO bus is already
> > accessible.
>
> We keep having issues with rtnl_lock taken from resume.
> Honestly, I'm not sure anyone has found a good solution, yet.
> Mostly people just don't implement runtime PM.
>
> If we were able to pass optional context to suspend/resume
> we could implement conditional locking. We'd lose a lot of
> self-respect but it'd make fixing such bugs easier..

Normal drivers have the option of separate callbacks for runtime PM
vs system suspend/resume states. It seems USB doesn't, just munging
everything into one pair of suspend and resume ops without any way
of telling them apart. I suggest that is part of the problem here.

However, I'm not a USB expert, so...

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