Re: [PATCH] [RFC] net: phy: Fix reboot crash if CONFIG_IP_PNP is not set

[Ioana Ciornei <ioana.ciornei@nxp.com>]

On Mon, Jan 04, 2021 at 06:31:05PM +0100, Andrew Lunn wrote:
> > The basic rules here should be, if the MDIO bus is registered, it is
> > usable. There are things like PHY statistics, HWMON temperature
> > sensors, etc, DSA switches, all which have a life cycle separate to
> > the interface being up.
> 
> [Goes and looks at the code]
> 
> Yes, this is runtime PM which is broken.
> 
> sh_mdio_init() needs to wrap the mdp->mii_bus->read and
> mdp->mii_bus->write calls with calls to
> 
> pm_runtime_get_sync(&mdp->pdev->dev);
> 
> and
> 
> pm_runtime_put_sync(&mdp->pdev->dev);
> 

Agree. Thanks for actually looking into it.. I'm not really well versed
in runtime PM.

> The KSZ8041RNLI supports statistics, which ethtool --phy-stats can
> read, and these will also going to cause problems.
> 

Not really, this driver connects to the PHY on .ndo_open(), thus any
try to actually dump the PHY statistics before an ifconfig up would get
an -EOPNOTSUPP since the dev->phydev is not yet populated.

This is exactly why I do not understand why some drivers insist on
calling of_phy_connect() and its variants on .ndo_open() and not while
probing the device - you can access the debug stats only if the
interface was started.