linux-kernel - Re: [PATCH net 3/3] net: phy: mscc: enable VSC8501/2 RGMII RX clock

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Message-ID: <ZGpcGbq47nL/rlEb@shell.armlinux.org.uk>
Date:   Sun, 21 May 2023 18:59:53 +0100
From:   "Russell King (Oracle)" <linux@...linux.org.uk>
To:     David Epping <david.epping@...singlinkelectronics.com>
Cc:     Andrew Lunn <andrew@...n.ch>,
        Heiner Kallweit <hkallweit1@...il.com>,
        "David S . Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, UNGLinuxDriver@...rochip.com
Subject: Re: [PATCH net 3/3] net: phy: mscc: enable VSC8501/2 RGMII RX clock

On Sat, May 20, 2023 at 06:06:03PM +0200, David Epping wrote:
> +static int vsc85xx_rgmii_enable_rx_clk(struct phy_device *phydev,
> +				       u32 rgmii_cntl)
> +{
> +	int rc, phy_id;
> +
> +	phy_id = phydev->drv->phy_id & phydev->drv->phy_id_mask;
> +	if (PHY_ID_VSC8501 != phy_id && PHY_ID_VSC8502 != phy_id)
> +		return 0;

As you are accessing the phy_id in the phy_driver struct, isn't it
already true that this will be initialised to constants such as
PHY_ID_VSC8501 or PHY_ID_VSC8502? In which case, why would you need
to mask it with drv->phy_id_mask ?

> +
> +	mutex_lock(&phydev->lock);
> +
> +	rc = phy_modify_paged(phydev, MSCC_PHY_PAGE_EXTENDED_2, rgmii_cntl,
> +			      VSC8502_RGMII_RX_CLK_DISABLE, 0);
> +
> +	mutex_unlock(&phydev->lock);

What is the purpose of taking this lock? phy_modify_paged() will do its
read-modify-write access and page accesses under the MDIO bus lock,
which should be all that's required to guarantee an atomic update.

-- 
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