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: <20250911075513.1d90f8b0@kernel.org>
Date: Thu, 11 Sep 2025 07:55:13 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: "Russell King (Oracle)" <linux@...linux.org.uk>
Cc: 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, 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..