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

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Date:   Mon, 30 Nov 2020 10:57:36 -0600
From:   Dan Murphy <dmurphy@...com>
To:     Andrew Lunn <andrew@...n.ch>
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

Andrew

On 11/19/20 7:49 PM, Andrew Lunn wrote:
>> +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.

OK.


>
>> +			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)?

According to the data sheet the FIFO depth is for RMII.

"Fifo depth for RMII Tx fifo"

But I will ask the HW team for clarification.


>
>> +#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.
Well this is only used once so I will just remove the of_node declaration
>
>> +#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.

The RGMII delay is fixed in the PHY.  The user can either turn it on or 
off. The default is 'off' which is 0.

I can explicitly set the rgmii_delay to 0 in non-OF cases.

Dan