Re: [PATCH net-next v2] net: phy: micrel: Add support for lan9645x internal phy

[Jens Emil Schulz Ostergaard <jensemil.schulzostergaard@microchip.com>]

On Wed, 2026-02-25 at 14:39 +0100, Andrew Lunn wrote:
> 
> > > > > > > +static int lan9645x_suspend(struct phy_device *phydev)
> > > > > > > +{
> > > > > > > +    int ret, val;
> > > > > > > +
> > > > > > > +    /* Force link down before software power down (SPD), by doing software
> > > > > > > +     * soft reset. This resets the PHY, but keeps all register configuration
> > > > > > > +     * intact. The bit self clears.
> > > > > > > +     *
> > > > > > > +     * This is needed as a workaround for an issue where performing SPD on a
> > > > > > > +     * port can bring adjacent ports down, when there is traffic flowing
> > > > > > > +     * through the ports.
> > > > > > > +     */
> > > > > > > +    ret = phy_modify(phydev, LAN9645X_CONTROL_REGISTER,
> > > > > > > +                     LAN9645X_CONTROL_REGISTER_SOFT_RESET, 1);
> > > > > 
> > > > > Any specific reason why you use a vendor-specific register here instead of BMCR
> > > > > via genphy_soft_reset()?
> > > > > 
> > > > > 
> > > > 
> > > > Sorry I missed your mail. genphy_soft_reset() will do a software (hard) reset via
> > > > bit 15 (BMCR_RESET). In particular it will reset the registers. We want to do
> > > > a software soft reset, which resets the PHY without changing register values.
> > > > 
> > > No, BMCR_RESET usually doesn't reset configuration registers. That's why the
> > > function is called genphy_*soft*_reset. In case your PHY behaves different,
> > > which configuration registers does it change?
> > > 
> > 
> > Ok I tought that was the usual behavior. The register spec says BMCR_RESET will reset
> > the PHY and all its registers to their default state.
> 
> Most PHYs do a soft reset when this bit is set, but some do a much
> harder reset, resetting all state including registers.
> 
> Does the documentation say anything about
> LAN9645X_CONTROL_REGISTER_SOFT_RESET and self clearing? BMCR_RESET
> should be cleared by the PHY when the reset is
> complete. genphy_soft_reset() uses phy_poll_reset() to wait for the
> bit to clear. If you don't wait, it could be your start writing to
> registers while the reset is still happening, and those writes get
> lost. You might have the same issue here.
> 
>       Andrew

Yes, it says the bit is self-clearing (R/W1S/SC). In the next version I
am currently setting the bit with phy_set_bits, and then poll for the bit
to clear with phy_read_poll_timeout.

Thanks,
Emil