netdev - Re: [PATCH net] net: phy: fix phy_uses_state

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Message-ID: <aLVosUZtXftPC-OY@shell.armlinux.org.uk>
Date: Mon, 1 Sep 2025 10:34:41 +0100
From: "Russell King (Oracle)" <linux@...linux.org.uk>
To: Andrew Lunn <andrew@...n.ch>, Heiner Kallweit <hkallweit1@...il.com>
Cc: "David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org,
	Paolo Abeni <pabeni@...hat.com>,
	Vladimir Oltean <vladimir.oltean@....com>
Subject: Re: [PATCH net] net: phy: fix phy_uses_state_machine()

On Sun, Aug 31, 2025 at 05:38:11PM +0100, Russell King (Oracle) wrote:
> phy_uses_state_machine() is called from the resume path (see
> mdio_bus_phy_resume()) which will be called for all devices whether
> they are connected to a network device or not.
> 
> phydev->phy_link_change is initialised by phy_attach_direct(), and
> overridden by phylink. This means that a never-connected PHY will
> have phydev->phy_link_change set to NULL, which causes
> phy_uses_state_machine() to return true. This is incorrect.
> 
> Fix the case where phydev->phy_link_change is NULL.
> 
> Reported-by: Xu Yang <xu.yang_2@....com>
> Link: https://lore.kernel.org/r/20250806082931.3289134-1-xu.yang_2@nxp.com
> Fixes: fc75ea20ffb4 ("net: phy: allow MDIO bus PM ops to start/stop state machine for phylink-controlled PHY")
> Signed-off-by: Russell King (Oracle) <rmk+kernel@...linux.org.uk>
> ---
> The provided Link: rather than Closes: is because there were two issues
> identified in that thread, and this patch only addresses one of them.
> Therefore, it is not correct to mark that issue closed.
> 
> Xu Yang reported this fixed the problem for him, and it is an oversight
> in the phy_uses_state_machine() test.

While looking at this after Vladimir's comments, I've realised that
phy_uses_state_machine() will also return true when a PHY has been
attached and detached by phylink - phydev->phy_link_change remains
set to phylink_phy_change after it has been detached. So, there will
definitely be a v2 for this.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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