linux-kernel - Re: [PATCH v2 1/2] net: phy: adin: enable configuration of the LP Termination Register

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Message-ID: <019bcd38dadb138fda4cf8b113c13b77a4581168.camel@gmail.com>
Date: Wed, 07 Jan 2026 10:18:35 +0000
From: Nuno Sá <noname.nuno@...il.com>
To: Andrew Lunn <andrew@...n.ch>, Osose Itua
 <osose.itua@...oirfairelinux.com>
Cc: netdev@...r.kernel.org, devicetree@...r.kernel.org, 
	linux-kernel@...r.kernel.org, michael.hennerich@...log.com, 
	jerome.oufella@...oirfairelinux.com
Subject: Re: [PATCH v2 1/2] net: phy: adin: enable configuration of the LP
 Termination Register

On Tue, 2025-12-23 at 10:36 +0100, Andrew Lunn wrote:
> > +static int adin_config_zptm100(struct phy_device *phydev)
> > +{
> > +	struct device *dev = &phydev->mdio.dev;
> > +	int reg;
> > +	int rc;
> > +
> > +	if (!(device_property_read_bool(dev, "adi,low-cmode-impedance")))
> > +		return 0;
> > +
> > +	/* set to 0 to configure for lowest common-mode impedance */
> > +	rc = phy_write_mmd(phydev, MDIO_MMD_VEND1, ADIN1300_B_100_ZPTM_DIMRX, 0x0);
> > +	if (rc < 0)
> > +		return rc;
> > +
> > +	reg = phy_read_mmd(phydev, MDIO_MMD_VEND1, ADIN1300_B_100_ZPTM_DIMRX);
> > +	if (reg < 0)
> > +		return reg;
> > +
> > +	if (!(reg & ADIN1300_B_100_ZPTM_EN_DIMRX)) {
> > +		phydev_err(phydev, "Failed to set lowest common-mode impedance.\n");
> > +		return -EINVAL;
> > +	}
> 
> Under what condition do you think this could happen? Do you think
> there are variants of the hardware which do not have this register?
> 
> 	Andrew

I think he's just reading back the register to make sure the value was really updated...
If we were going to that for every write our lives would be miserable :).

I looked at both adin1200 and adin1300 and they support this in the same way so the above
should just be:

return phy_write_mmd()...

- Nuno Sá