linux-kernel - Re: [PATCH v3] net: phy: add driver for Motorcomm yt8511 phy

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Message-ID: <20210514130908.GD12395@shell.armlinux.org.uk>
Date:   Fri, 14 May 2021 14:09:08 +0100
From:   "Russell King (Oracle)" <linux@...linux.org.uk>
To:     Peter Geis <pgwipeout@...il.com>
Cc:     Andrew Lunn <andrew@...n.ch>,
        Heiner Kallweit <hkallweit1@...il.com>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org, linux-rockchip@...ts.infradead.org
Subject: Re: [PATCH v3] net: phy: add driver for Motorcomm yt8511 phy

Hi!

On Fri, May 14, 2021 at 07:58:26AM -0400, Peter Geis wrote:
> +	/* set rgmii delay mode */
> +	val = __phy_read(phydev, YT8511_PAGE);
> +
> +	switch (phydev->interface) {
> +	case PHY_INTERFACE_MODE_RGMII:
> +		val &= ~(YT8511_DELAY_RX | YT8511_DELAY_TX);
> +		break;
> +	case PHY_INTERFACE_MODE_RGMII_ID:
> +		val |= YT8511_DELAY_RX | YT8511_DELAY_TX;
> +		break;
> +	case PHY_INTERFACE_MODE_RGMII_RXID:
> +		val &= ~(YT8511_DELAY_TX);
> +		val |= YT8511_DELAY_RX;
> +		break;
> +	case PHY_INTERFACE_MODE_RGMII_TXID:
> +		val &= ~(YT8511_DELAY_RX);
> +		val |= YT8511_DELAY_TX;
> +		break;
> +	default: /* leave everything alone in other modes */
> +		break;
> +	}
> +
> +	ret = __phy_write(phydev, YT8511_PAGE, val);
> +	if (ret < 0)
> +		goto err_restore_page;

Another way of writing the above is to set "val" to be the value of the
YT8511_DELAY_RX and YT8511_DELAY_TX bits, and then do:

	ret = __phy_modify(phydev, YT8511_PAGE,
			   (YT8511_DELAY_RX | YT8511_DELAY_TX), val);
	if (ret < 0)
		goto err_restore_page;

which moves the read-modify-write out of the driver into core code and
makes the driver code smaller. It also handles your missing error check
on __phy_read() above - would you want the above code to attempt to
write a -ve error number back to this register? I suspect not!

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