Re: [PATCH net] net: phy: fix phy_uses_state_machine()

[Vladimir Oltean <vladimir.oltean@nxp.com>]

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@nxp.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@armlinux.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.
> 
>  drivers/net/phy/phy_device.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/phy/phy_device.c b/drivers/net/phy/phy_device.c
> index 7556aa3dd7ee..e6a673faabe6 100644
> --- a/drivers/net/phy/phy_device.c
> +++ b/drivers/net/phy/phy_device.c
> @@ -288,7 +288,7 @@ static bool phy_uses_state_machine(struct phy_device *phydev)
>  		return phydev->attached_dev && phydev->adjust_link;
>  
>  	/* phydev->phy_link_change is implicitly phylink_phy_change() */

We should either update this comment to clarify that the function
pointer is only set to phylink_phy_change() if set at all, or do away
with the comment entirely. Otherwise, it doesn't make much sense.

With that:

Reviewed-by: Vladimir Oltean <vladimir.oltean@nxp.com>

> -	return true;
> +	return !!phydev->phy_link_change;
>  }
>  
>  static bool mdio_bus_phy_may_suspend(struct phy_device *phydev)
> -- 
> 2.47.2
>