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Subject: Re: [PATCH 1/2] net: phy: micrel.c: add rgmii interface delay
 possibility to ksz9131
To:     Philippe Schenker <philippe.schenker@toradex.com>, andrew@lunn.ch,
        f.fainelli@gmail.com, linux@armlinux.org.uk,
        netdev@vger.kernel.org, robh+dt@kernel.org,
        devicetree@vger.kernel.org, shawnguo@kernel.org,
        mark.rutland@arm.com
Cc:     o.rempel@pengutronix.de, linux-kernel@vger.kernel.org,
        silvan.murer@gmail.com, s.hauer@pengutronix.de,
        a.fatoum@pengutronix.de, "David S. Miller" <davem@davemloft.net>
References: <20200325150329.228329-1-philippe.schenker@toradex.com>
From:   Heiner Kallweit <hkallweit1@gmail.com>
Message-ID: <d1067087-2cb8-f7c7-7929-2c4c9d2a4cb3@gmail.com>
Date:   Wed, 25 Mar 2020 16:24:00 +0100
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On 25.03.2020 16:03, Philippe Schenker wrote:
> The KSZ9131 provides DLL controlled delays on RXC and TXC lines. This
> patch makes use of those delays. The information which delays should
> be enabled or disabled comes from the interface names, documented in
> ethernet-controller.yaml:
> 
> rgmii:      Disable RXC and TXC delays
> rgmii-id:   Enable RXC and TXC delays
> rgmii-txid: Enable only TXC delay, disable RXC delay
> rgmii-rxid: Enable onlx RXC delay, disable TXC delay
> 
> Signed-off-by: Philippe Schenker <philippe.schenker@toradex.com>
> ---
> 
>  drivers/net/phy/micrel.c | 45 ++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 45 insertions(+)
> 
> diff --git a/drivers/net/phy/micrel.c b/drivers/net/phy/micrel.c
> index 63dedec0433d..d3ad09774847 100644
> --- a/drivers/net/phy/micrel.c
> +++ b/drivers/net/phy/micrel.c
> @@ -704,6 +704,48 @@ static int ksz9131_of_load_skew_values(struct phy_device *phydev,
>  	return phy_write_mmd(phydev, 2, reg, newval);
>  }
>  
> +/* MMD Address 0x2 */
> +#define KSZ9131RN_RXC_DLL_CTRL		76
> +#define KSZ9131RN_TXC_DLL_CTRL		77
> +#define KSZ9131RN_DLL_CTRL_BYPASS	BIT_MASK(12)
> +#define KSZ9131RN_DLL_ENABLE_DELAY	0
> +#define KSZ9131RN_DLL_DISABLE_DELAY	BIT(12)
> +
> +static int ksz9131_config_rgmii_delay(struct phy_device *phydev)
> +{
> +	int ret;
> +	u16 rxcdll_val, txcdll_val;
> +

Reverse xmas tree order please.

> +	switch (phydev->interface) {
> +	case PHY_INTERFACE_MODE_RGMII:
> +		rxcdll_val = KSZ9131RN_DLL_DISABLE_DELAY;
> +		txcdll_val = KSZ9131RN_DLL_DISABLE_DELAY;
> +		break;
> +	case PHY_INTERFACE_MODE_RGMII_ID:
> +		rxcdll_val = KSZ9131RN_DLL_ENABLE_DELAY;
> +		txcdll_val = KSZ9131RN_DLL_ENABLE_DELAY;
> +		break;
> +	case PHY_INTERFACE_MODE_RGMII_RXID:
> +		rxcdll_val = KSZ9131RN_DLL_ENABLE_DELAY;
> +		txcdll_val = KSZ9131RN_DLL_DISABLE_DELAY;
> +		break;
> +	case PHY_INTERFACE_MODE_RGMII_TXID:
> +		rxcdll_val = KSZ9131RN_DLL_DISABLE_DELAY;
> +		txcdll_val = KSZ9131RN_DLL_ENABLE_DELAY;
> +		break;
> +	default:
> +		return 0;
> +	}
> +
> +	ret = phy_modify_mmd_changed(phydev, 2, KSZ9131RN_RXC_DLL_CTRL,
> +				     KSZ9131RN_DLL_CTRL_BYPASS, rxcdll_val);
> +	if (ret < 0)
> +		return ret;
> +
> +	return phy_modify_mmd_changed(phydev, 2, KSZ9131RN_TXC_DLL_CTRL,
> +				     KSZ9131RN_DLL_CTRL_BYPASS, txcdll_val);

phy_modify_mmd_changed() returns 1 if the register value was changed,
and that's not what you want here. Simply use phy_modify_mmd() in both
occurrences. And your function has a return value, but it's not used by
the caller.

> +}
> +
>  static int ksz9131_config_init(struct phy_device *phydev)
>  {
>  	const struct device *dev = &phydev->mdio.dev;
> @@ -730,6 +772,9 @@ static int ksz9131_config_init(struct phy_device *phydev)
>  	if (!of_node)
>  		return 0;
>  
> +	if (phy_interface_is_rgmii(phydev))
> +		ksz9131_config_rgmii_delay(phydev);
> +
>  	ret = ksz9131_of_load_skew_values(phydev, of_node,
>  					  MII_KSZ9031RN_CLK_PAD_SKEW, 5,
>  					  clk_skews, 2);
>