netdev - Re: [PATCH net v3] net: phy: marvell: add Marvell specific PHY loopback

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Date:   Fri, 14 Jan 2022 21:34:03 +0100
From:   Heiner Kallweit <hkallweit1@...il.com>
To:     Mohammad Athari Bin Ismail <mohammad.athari.ismail@...el.com>,
        Andrew Lunn <andrew@...n.ch>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Oleksij Rempel <linux@...pel-privat.de>,
        Russell King <linux@...linux.org.uk>
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org
Subject: Re: [PATCH net v3] net: phy: marvell: add Marvell specific PHY
 loopback

On 13.01.2022 10:56, Mohammad Athari Bin Ismail wrote:
> Existing genphy_loopback() is not applicable for Marvell PHY. Besides
> configuring bit-6 and bit-13 in Page 0 Register 0 (Copper Control
> Register), it is also required to configure same bits  in Page 2
> Register 21 (MAC Specific Control Register 2) according to speed of
> the loopback is operating.
> 
> Tested working on Marvell88E1510 PHY for all speeds (1000/100/10Mbps).
> 
> FIXME: Based on trial and error test, it seem 1G need to have delay between
> soft reset and loopback enablement.
> 
> Fixes: 014068dcb5b1 ("net: phy: genphy_loopback: add link speed configuration")
> Cc: <stable@...r.kernel.org> # 5.15.x
> Signed-off-by: Mohammad Athari Bin Ismail <mohammad.athari.ismail@...el.com>
> ---
> v3 changelog:
> - Use phy_write() to configure speed for BMCR.
> - Add error handling.
> All commented by Russell King <linux@...linux.org.uk>
> 
> v2 changelog:
> - For loopback enabled, add bit-6 and bit-13 configuration in both Page
>   0 Register 0 and Page 2 Register 21. Commented by Heiner Kallweit
> <hkallweit1@...il.com>.
> - For loopback disabled, follow genphy_loopback() implementation
> ---
>  drivers/net/phy/marvell.c | 56 ++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 55 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/net/phy/marvell.c b/drivers/net/phy/marvell.c
> index 4fcfca4e1702..5c371c2de9a0 100644
> --- a/drivers/net/phy/marvell.c
> +++ b/drivers/net/phy/marvell.c
> @@ -189,6 +189,8 @@
>  #define MII_88E1510_GEN_CTRL_REG_1_MODE_RGMII_SGMII	0x4
>  #define MII_88E1510_GEN_CTRL_REG_1_RESET	0x8000	/* Soft reset */
>  
> +#define MII_88E1510_MSCR_2		0x15
> +
>  #define MII_VCT5_TX_RX_MDI0_COUPLING	0x10
>  #define MII_VCT5_TX_RX_MDI1_COUPLING	0x11
>  #define MII_VCT5_TX_RX_MDI2_COUPLING	0x12
> @@ -1932,6 +1934,58 @@ static void marvell_get_stats(struct phy_device *phydev,
>  		data[i] = marvell_get_stat(phydev, i);
>  }
>  
> +static int marvell_loopback(struct phy_device *phydev, bool enable)

Marvell PHY's use different bits for the loopback speed, e.g.:

88E1510 bits 13, 6
88E1545 bits 2..0

Your function is usable with certain Marvell PHY's only, therefore
the function name is misleading. At a first glance I see two options:

1. Leave the function name and add a version-specific section that returns
   an error for (not yet) supported versions.
2. Name it m88e1510_loopback()

> +{
> +	int err;
> +
> +	if (enable) {
> +		u16 bmcr_ctl = 0, mscr2_ctl = 0;
> +
> +		if (phydev->speed == SPEED_1000)
> +			bmcr_ctl = BMCR_SPEED1000;
> +		else if (phydev->speed == SPEED_100)
> +			bmcr_ctl = BMCR_SPEED100;
> +
> +		if (phydev->duplex == DUPLEX_FULL)
> +			bmcr_ctl |= BMCR_FULLDPLX;
> +
> +		err = phy_write(phydev, MII_BMCR, bmcr_ctl);
> +		if (err < 0)
> +			return err;
> +
> +		if (phydev->speed == SPEED_1000)
> +			mscr2_ctl = BMCR_SPEED1000;
> +		else if (phydev->speed == SPEED_100)
> +			mscr2_ctl = BMCR_SPEED100;
> +
> +		err = phy_modify_paged(phydev, MII_MARVELL_MSCR_PAGE,
> +				       MII_88E1510_MSCR_2, BMCR_SPEED1000 |
> +				       BMCR_SPEED100, mscr2_ctl);
> +		if (err < 0)
> +			return err;
> +
> +		/* Need soft reset to have speed configuration takes effect */
> +		err = genphy_soft_reset(phydev);
> +		if (err < 0)
> +			return err;
> +
> +		/* FIXME: Based on trial and error test, it seem 1G need to have
> +		 * delay between soft reset and loopback enablement.
> +		 */
> +		if (phydev->speed == SPEED_1000)
> +			msleep(1000);
> +
> +		return phy_modify(phydev, MII_BMCR, BMCR_LOOPBACK,
> +				  BMCR_LOOPBACK);
> +	} else {
> +		err = phy_modify(phydev, MII_BMCR, BMCR_LOOPBACK, 0);
> +		if (err < 0)
> +			return err;
> +
> +		return phy_config_aneg(phydev);
> +	}
> +}
> +
>  static int marvell_vct5_wait_complete(struct phy_device *phydev)
>  {
>  	int i;
> @@ -3078,7 +3132,7 @@ static struct phy_driver marvell_drivers[] = {
>  		.get_sset_count = marvell_get_sset_count,
>  		.get_strings = marvell_get_strings,
>  		.get_stats = marvell_get_stats,
> -		.set_loopback = genphy_loopback,
> +		.set_loopback = marvell_loopback,
>  		.get_tunable = m88e1011_get_tunable,
>  		.set_tunable = m88e1011_set_tunable,
>  		.cable_test_start = marvell_vct7_cable_test_start,