linux-kernel - Re: [PATCH net-next v4 4/4] net: phy: dp83td510: Add support for the DP83TD510 Ethernet PHY

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Message-ID: <20201120014919.GB1804098@lunn.ch>
Date:   Fri, 20 Nov 2020 02:49:19 +0100
From:   Andrew Lunn <andrew@...n.ch>
To:     Dan Murphy <dmurphy@...com>
Cc:     davem@...emloft.net, f.fainelli@...il.com, hkallweit1@...il.com,
        robh@...nel.org, ciorneiioana@...il.com,
        devicetree@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next v4 4/4] net: phy: dp83td510: Add support for the
 DP83TD510 Ethernet PHY

> +static int dp83td510_config_init(struct phy_device *phydev)
> +{
> +	struct dp83td510_private *dp83td510 = phydev->priv;
> +	int ret = 0;
> +
> +	if (phy_interface_is_rgmii(phydev)) {

> +		if (dp83td510->rgmii_delay) {
> +			ret = phy_set_bits_mmd(phydev, DP83TD510_DEVADDR,
> +					       DP83TD510_MAC_CFG_1,
> +					       dp83td510->rgmii_delay);

Just to be safe, you should always write rgmii_delay, even if it is
zero. We have had too many bugs with RGMII delays which cause bad
backwards compatibility problems, so i would prefer to do a write
which might be unneeded, that find a bug here in a few years time.

> +			if (ret)
> +				return ret;
> +		}
> +	}
> +
> +	if (phydev->interface == PHY_INTERFACE_MODE_RMII) {
> +		ret = phy_modify(phydev, DP83TD510_GEN_CFG,
> +				 DP83TD510_FIFO_DEPTH_MASK,
> +				 dp83td510->tx_fifo_depth);

So there is no need to set the FIFO depth for the other three RGMII
modes? Or should this also be phy_interface_is_rgmii(phydev)?

> +#if IS_ENABLED(CONFIG_OF_MDIO)
> +static int dp83td510_of_init(struct phy_device *phydev)
> +{
> +	struct dp83td510_private *dp83td510 = phydev->priv;
> +	struct device *dev = &phydev->mdio.dev;
> +	struct device_node *of_node = dev->of_node;

You need to move this assignment to later in order to keep with
reverse christmas tree.

> +#else
> +static int dp83869_of_init(struct phy_device *phydev)
> +{
> +	dp83td510->hi_diff_output = DP83TD510_2_4V_P2P
> +	dp83td510->tx_fifo_depth = DP83TD510_FIFO_DEPTH_5_B_NIB

You don't have DT, so there is no fine control, but you still need to
do the basic 2ns delay as indicated by the phydev->interface value. So
i think you still need to set dp83td510->rgmii_delay depending on
which RGMII mode is requested.

      Andrew