linux-kernel - 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: <22773d93-cbad-41c5-9e79-4d7f6b9e5ec0@rowland.harvard.edu>
Date: Thu, 11 Sep 2025 22:30:09 -0400
From: Alan Stern <stern@...land.harvard.edu>
To: "Russell King (Oracle)" <linux@...linux.org.uk>
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 Thu, Sep 11, 2025 at 09:46:35PM +0100, Russell King (Oracle) wrote:
> On Thu, Sep 11, 2025 at 07:55:13AM -0700, Jakub Kicinski wrote:
> > 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...

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.

Alan Stern