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Date:   Wed, 29 Sep 2021 17:53:39 +0200
From:   Andrew Lunn <andrew@lunn.ch>
To:     Russell King <rmk+kernel@armlinux.org.uk>
Cc:     Heiner Kallweit <hkallweit1@gmail.com>,
        "David S. Miller" <davem@davemloft.net>, netdev@vger.kernel.org,
        Marek Beh__n <kabel@kernel.org>,
        Jakub Kicinski <kuba@kernel.org>
Subject: Re: [PATCH v2 net-next] net: phy: marvell10g: add downshift tunable
 support
Message-ID: <YVSMAyxgJSqz+gRk@lunn.ch>
References: <E1mVbVt-0004Fh-Dv@rmk-PC.armlinux.org.uk>
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> +static int mv3310_set_downshift(struct phy_device *phydev, u8 ds)
> +{
> +	struct mv3310_priv *priv = dev_get_drvdata(&phydev->mdio.dev);
> +	u16 val;
> +	int err;
> +
> +	if (!priv->has_downshift)
> +		return -EOPNOTSUPP;
> +
> +	if (ds == DOWNSHIFT_DEV_DISABLE)
> +		return phy_clear_bits_mmd(phydev, MDIO_MMD_PCS, MV_PCS_DSC1,
> +					  MV_PCS_DSC1_ENABLE);
> +
> +	/* DOWNSHIFT_DEV_DEFAULT_COUNT is confusing. It looks like it should
> +	 * set the default settings for the PHY. However, it is used for
> +	 * "ethtool --set-phy-tunable ethN downshift on". The intention is
> +	 * to enable downshift at a default number of retries. The default
> +	 * settings for 88x3310 are for two retries with downshift disabled.
> +	 * So let's use two retries with downshift enabled.
> +	 */
> +	if (ds == DOWNSHIFT_DEV_DEFAULT_COUNT)
> +		ds = 2;

That is sensible and explains what is going on. Thanks.

Reviewed-by: Andrew Lunn <andrew@lunn.ch>

    Andrew