Re: [RFC PATCH] net: phy: micrel: reset KSZ9x31 when resuming

[Andrew Lunn <andrew@lunn.ch>]

On Tue, Feb 06, 2024 at 06:26:45PM +0100, Francesco Dolcini wrote:
> On Wed, Jan 17, 2024 at 02:33:53PM +0100, Wolfram Sang wrote:
> > > > +static int ksz9x31_resume(struct phy_device *phydev)
> > > > +{
> > > > +	phy_device_reset(phydev, 1);
> > > > +	phy_device_reset(phydev, 0);
> > > 
> > > Is something like that fine?
> > > Don't we need to reconfigure the ethernet phy completely on resume
> > > if we do reset it? kszphy_config_reset() is taking care of something,
> > > but I think that the phy being reset on resume is not handled
> > > correctly.
> > 
> > If the interface is up before suspending, then suspend will assert the
> > reset-line. If the interface is disabled before suspending, then close
> > will assert the reset line. Deassertion will happen on resume/open.
> > 
> > So, unless I am overlooking something, my code does not really add
> > something new. It only makes sure that the reset line always gets
> > asserted before deasserting. Because in the case that the interface has
> > never been up before, there is no instance which could assert reset. Or,
> > at least, I could not find one.
> > 
> > Makes sense? Tests work fine here, at least.
> 
> What I do not know, is what happen to any configuration that was done to
> the phy before.

I'm assuming here WoL was not enabled, so the PHY did actually
suspend.

mdio_bus_phy_suspend() calls phy_stop_machine() which will set the
state of the PHY to UP.

During resume mdio_bus_phy_resume() calls phy_init_hw(). That should
do a soft reset, call the config_init() callback, and configure
interrupts. After that phy_resume() is called and then
phy_state_machine(). Do to setting the state to UP, the state machine
will kick off auto-negotiation, which will cause any auto-neg
parameters to be written to the PHY.

> What if you have disabled gigabit ethernet from auto negotiation before
> suspend, it will be enabled again after the phy get out of reset.

If you have set in fixed mode, the wrongly named phy_config_aneg()
will set the fixed modes, same as it would set the auto-neg modes. So
they should be preserved over suspend/resume.
 
	Andrew