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

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Message-ID: <YqSxtvZUEmaxmihV@lunn.ch>
Date:   Sat, 11 Jun 2022 17:16:06 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Oleksij Rempel <o.rempel@...gutronix.de>
Cc:     Heiner Kallweit <hkallweit1@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, kernel@...gutronix.de,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH net-next v3 3/3] net: phy: dp83td510: disable cable test
 support for 1Vpp PHYs

>  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?

       Andrew