linux-kernel - Re: [PATCH net-next v3 3/3] net: phy: dp83td510: disable cable test support for 1Vpp PHYs

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Date:   Sat, 11 Jun 2022 17:23:02 +0200
From:   Marc Kleine-Budde <mkl@...gutronix.de>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     Oleksij Rempel <o.rempel@...gutronix.de>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, Eric Dumazet <edumazet@...gle.com>,
        kernel@...gutronix.de, Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        "David S. Miller" <davem@...emloft.net>,
        Heiner Kallweit <hkallweit1@...il.com>
Subject: Re: [PATCH net-next v3 3/3] net: phy: dp83td510: disable cable test
 support for 1Vpp PHYs

On 11.06.2022 17:16:06, Andrew Lunn wrote:
> >  static int dp83td510_cable_test_start(struct phy_device *phydev)
> >  {
> > -	int ret;
> > +	struct dp83td510_priv *priv = phydev->priv;
> > +	int ret, cfg = 0;
> > +
> > +	/* Generate 2.4Vpp pulse if HW is allowed to do so */
> > +	if (priv->allow_v2_4_mode) {
> > +		cfg |= DP83TD510E_TDR_TX_TYPE;
> > +	} else {
> > +		/* This PHY do not provide usable results with 1Vpp pulse.
> 
> s/do/does
> 
> 
> > +		 * Potentially different dp83td510_tdr_init() values are
> > +		 * needed.
> > +		 */
> > +		return -EOPNOTSUPP;
> > +	}
> 
> I don't remember the details for v2.4. Is it possible to change up
> from 1v to 2.4v for the duration of the cable test? Is there a danger
> to damage the link peer? I guess not, since you need to pass EMC
> testing which zaps it with 100Kv or something. So is this more a local
> supply issue?

In some industrial areas (e.g. ATEX (explosion protection)) 2.4V is not
allowed due to regulations. If the PHY is strapped to 1.0V we assume for
now this has a good reason and don't crank up the voltage :)

regards,
Marc

-- 
Pengutronix e.K.                 | Marc Kleine-Budde           |
Embedded Linux                   | https://www.pengutronix.de  |
Vertretung West/Dortmund         | Phone: +49-231-2826-924     |
Amtsgericht Hildesheim, HRA 2686 | Fax:   +49-5121-206917-5555 |

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