netdev - Re: [PATCH net v2] net: phy: marvell: add Marvell specific PHY loopback

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Date:   Wed, 12 Jan 2022 13:12:53 +0000
From:   "Russell King (Oracle)" <linux@...linux.org.uk>
To:     Mohammad Athari Bin Ismail <mohammad.athari.ismail@...el.com>
Cc:     Andrew Lunn <andrew@...n.ch>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Oleksij Rempel <linux@...pel-privat.de>,
        Heiner Kallweit <hkallweit1@...il.com>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH net v2] net: phy: marvell: add Marvell specific PHY
 loopback

On Wed, Jan 12, 2022 at 05:33:44PM +0800, Mohammad Athari Bin Ismail wrote:
> +static int marvell_loopback(struct phy_device *phydev, bool enable)
> +{
> +	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;
> +
> +		phy_modify(phydev, MII_BMCR, ~0, bmcr_ctl);

Is there any point in doing a read-modify-write here if you're just
setting all bits in the register? Wouldn't phy_write() be more
appropriate? What about error handing?

> +
> +		if (phydev->speed == SPEED_1000)
> +			mscr2_ctl = BMCR_SPEED1000;
> +		else if (phydev->speed == SPEED_100)
> +			mscr2_ctl = BMCR_SPEED100;
> +
> +		phy_modify_paged(phydev, MII_MARVELL_MSCR_PAGE,
> +				 MII_88E1510_MSCR_2, BMCR_SPEED1000 |
> +				 BMCR_SPEED100, mscr2_ctl);
> +
> +		/* Need soft reset to have speed configuration takes effect */
> +		genphy_soft_reset(phydev);
> +
> +		/* 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 {
> +		phy_modify(phydev, MII_BMCR, BMCR_LOOPBACK, 0);

Error handling?

Thanks.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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