linux-kernel - Re: [PATCH net-next v8 4/4] net: dsa: add basic initial driver for MxL862xx switches

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Message-ID: <c2e191c4-dec4-4e42-b108-353778d9bd18@redhat.com>
Date: Tue, 27 Jan 2026 11:41:00 +0100
From: Paolo Abeni <pabeni@...hat.com>
To: Daniel Golle <daniel@...rotopia.org>, Andrew Lunn <andrew@...n.ch>,
 Vladimir Oltean <olteanv@...il.com>, "David S. Miller"
 <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 Jakub Kicinski <kuba@...nel.org>, Rob Herring <robh@...nel.org>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley
 <conor+dt@...nel.org>, Heiner Kallweit <hkallweit1@...il.com>,
 Russell King <linux@...linux.org.uk>, Simon Horman <horms@...nel.org>,
 netdev@...r.kernel.org, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org
Cc: Frank Wunderlich <frankwu@....de>, Chad Monroe <chad@...roe.io>,
 Cezary Wilmanski <cezary.wilmanski@...ran.com>,
 Avinash Jayaraman <ajayaraman@...linear.com>, Bing tao Xu
 <bxu@...linear.com>, Liang Xu <lxu@...linear.com>,
 Juraj Povazanec <jpovazanec@...linear.com>,
 "Fanni (Fang-Yi) Chan" <fchan@...linear.com>,
 "Benny (Ying-Tsan) Weng" <yweng@...linear.com>,
 "Livia M. Rosu" <lrosu@...linear.com>, John Crispin <john@...ozen.org>
Subject: Re: [PATCH net-next v8 4/4] net: dsa: add basic initial driver for
 MxL862xx switches

On 1/22/26 4:42 AM, Daniel Golle wrote:
> +static int mxl862xx_send_cmd(struct mxl862xx_priv *priv, u16 cmd, u16 size,
> +			     bool quiet)
> +{
> +	int ret;
> +
> +	ret = mxl862xx_reg_write(priv, MXL862XX_MMD_REG_LEN_RET, size);
> +	if (ret)
> +		return ret;
> +
> +	ret = mxl862xx_reg_write(priv, MXL862XX_MMD_REG_CTRL,
> +				 cmd | CTRL_BUSY_MASK);
> +	if (ret)
> +		return ret;
> +
> +	ret = mxl862xx_busy_wait(priv);
> +	if (ret)
> +		return ret;
> +
> +	ret = mxl862xx_reg_read(priv, MXL862XX_MMD_REG_LEN_RET);
> +	/* handle errors returned by the firmware as -EIO
> +	 * The firmware is based on Zephyr OS and uses the errors as
> +	 * defined in errno.h of Zephyr OS. See
> +	 * https://github.com/zephyrproject-rtos/zephyr/blob/v3.7.0/lib/libc/minimal/include/errno.h
> +	 */
> +	if ((s16)ret < 0) {

The cast is likely not needed above? if `ret` values < S16_MIN are
possible this will return such values to the caller without the IO err
printk.

> +		if (!quiet)
> +			dev_err(&priv->mdiodev->dev,
> +				"CMD %04x returned error %d\n", cmd, (s16)ret);
> +		return -EIO;
> +	}
> +
> +	return ret;
> +}
> +
> +int mxl862xx_api_wrap(struct mxl862xx_priv *priv, u16 cmd, void *_data,
> +		      u16 size, bool read, bool quiet)
> +{
> +	__le16 *data = _data;
> +	u16 max, i;
> +	int ret, cmd_ret;

Minor nit: reverse christmas tree above.

BTW the initial port isolation LGTM, but I would appreciate some DSA
expert second opinion.

Thanks,

Paolo