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

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Message-ID: <20230521134356.ar3itavhdypnvasc@skbuf>
Date:   Sun, 21 May 2023 16:43:56 +0300
From:   Vladimir Oltean <olteanv@...il.com>
To:     David Epping <david.epping@...singlinkelectronics.com>
Cc:     Andrew Lunn <andrew@...n.ch>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Russell King <linux@...linux.org.uk>,
        "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:
> +/* For VSC8501 and VSC8502 the RGMII RX clock output is disabled by default. */
> +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;

Not only bit 11 is reserved for VSC8530, but it's also read-only, so it
should not matter what is written there.

Since vsc85xx_rgmii_enable_rx_clk() and vsc85xx_rgmii_set_skews() write
to the same register, would it not make sense to combine the two into a
single phy_modify_paged() call, and to zeroize bit 11 as part of that?

The other caller of vsc85xx_rgmii_set_skews(), VSC8572, unfortunately
does not document bit 11 at all - it doesn't say if it's read-only or not.
We could conditionally include the VSC8502_RGMII_RX_CLK_DISABLE bit in the
"mask" argument of phy_modify_paged() based on rgmii_cntl == VSC8502_RGMII_CNTL,
such as to exclude VSC8572.

What do you think?