RE: [PATCH net] net: phy: micrel: Fix MMD register access during SPD in ksz9131_resume()

[Ovidiu Panait]

Hi,

> 
> On Fri, Apr 03, 2026 at 11:17:38AM +0000, Ovidiu Panait wrote:
> > During system suspend, phy_suspend() puts the PHY into Software Power-
> Down
> > (SPD) by setting the BMCR_PDOWN bit in MII_BMCR. According to the
> KSZ9131
> > datasheet, MMD register access is restricted during SPD:
> >
> >   - Only access to the standard registers (0 through 31) is supported.
> >   - Access to MMD address spaces other than MMD address space 1 is
> >     possible if the spd_clock_gate_override bit is set.
> >   - Access to MMD address space 1 is not possible.
> >
> > However, ksz9131_resume() calls ksz9131_config_rgmii_delay() before
> > kszphy_resume() clears BMCR_PDOWN. This means MMD registers are accessed
> > while the PHY is still in SPD, contrary to the datasheet.
> >
> > Additionally, on platforms where the PHY loses power during suspend
> > (e.g. RZ/G3E), all settings from ksz9131_config_init(), not just the
> > RGMII delays, are lost and need to be restored. When the MAC driver
> > sets mac_managed_pm (e.g. stmmac), mdio_bus_phy_resume() is skipped,
> > so phy_init_hw() (which calls config_init to restore all PHY settings)
> > is never invoked during resume.
> >
> > Fix this by replacing the RGMII delay restoration with a call to
> > phy_init_hw(), which takes the PHY out of SPD and performs full
> > reinitialization.
> >
> > Fixes: f25a7eaa897f ("net: phy: micrel: Add ksz9131_resume()")
> > Signed-off-by: Ovidiu Panait <ovidiu.panait.rb@xxxxxxxxxxx>
> > ---
> >  drivers/net/phy/micrel.c | 9 +++++++--
> >  1 file changed, 7 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/net/phy/micrel.c b/drivers/net/phy/micrel.c
> > index 2aa1dedd21b8..4236dbf4ad6b 100644
> > --- a/drivers/net/phy/micrel.c
> > +++ b/drivers/net/phy/micrel.c
> > @@ -6016,8 +6016,13 @@ static int lan8841_suspend(struct phy_device
> *phydev)
> >
> >  static int ksz9131_resume(struct phy_device *phydev)
> >  {
> > -	if (phydev->suspended && phy_interface_is_rgmii(phydev))
> > -		ksz9131_config_rgmii_delay(phydev);
> > +	int ret;
> > +
> > +	if (phydev->suspended) {
> > +		ret = phy_init_hw(phydev);
> > +		if (ret)
> > +			return ret;
> > +	}
> >
> >  	return kszphy_resume(phydev);
> >  }
> 
> mdio_bus_phy_resume():
> 
>         ret = phy_init_hw(phydev);
>         if (ret < 0)
>                 return ret;
> 
>         ret = phy_resume(phydev);
>         if (ret < 0)
>                 return ret;
> 
> where phy_resume() calls your resume function.
> 
> If a MAC driver is handling suspend/resume by setting
> phydev->mac_managed_pm then maybe the MAC driver should also be
> issuing phy_init_hw() before calling phy_resume() ?
> 
> Which MAC driver are you seeing a problem with?
> 

On my board the KSZ9131RNX PHY is paired to stmmac.

I could add phy_init_hw() before the phylink_prepare_resume() call, which
does the phy_resume() and remove the ksz9131_config_rgmii_delay() call from
ksz9131_resume(), as it is not correct/complete.

Ovidiu


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