linux-kernel - Re: [PATCH net-next v9 3/3] net: dsa: yt921x: Add support for Motorcomm YT921x

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Message-ID: <20250915103019.GP224143@horms.kernel.org>
Date: Mon, 15 Sep 2025 11:30:19 +0100
From: Simon Horman <horms@...nel.org>
To: David Yang <mmyangfl@...il.com>
Cc: netdev@...r.kernel.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>, Paolo Abeni <pabeni@...hat.com>,
	Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Russell King <linux@...linux.org.uk>, devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next v9 3/3] net: dsa: yt921x: Add support for
 Motorcomm YT921x

On Sat, Sep 13, 2025 at 12:44:01PM +0800, David Yang wrote:
> Motorcomm YT921x is a series of ethernet switches developed by Shanghai
> Motorcomm Electronic Technology, including:
> 
>   - YT9215S / YT9215RB / YT9215SC: 5 GbE PHYs
>   - YT9213NB / YT9214NB: 2 GbE PHYs
>   - YT9218N / YT9218MB: 8 GbE PHYs
> 
> and up to 2 GMACs.
> 
> Driver verified on a stock wireless router with IPQ5018 + YT9215S.
> 
> Signed-off-by: David Yang <mmyangfl@...il.com>

...

> +static int
> +yt921x_port_config(struct yt921x_priv *priv, int port, unsigned int mode,
> +		   phy_interface_t interface)
> +{
> +	struct device *dev = to_device(priv);
> +	u32 mask;
> +	u32 ctrl;
> +	int res;
> +
> +	if (!yt921x_port_is_external(port)) {
> +		if (interface != PHY_INTERFACE_MODE_INTERNAL) {
> +			dev_err(dev, "Wrong mode %d on port %d\n",
> +				interface, port);
> +			return -EINVAL;
> +		}
> +		return 0;
> +	}
> +
> +	switch (interface) {
> +	/* SGMII */
> +	case PHY_INTERFACE_MODE_SGMII:
> +	case PHY_INTERFACE_MODE_100BASEX:
> +	case PHY_INTERFACE_MODE_1000BASEX:
> +	case PHY_INTERFACE_MODE_2500BASEX:
> +		mask = YT921X_SGMII_CTRL_PORTn(port);
> +		res = yt921x_reg_set_bits(priv, YT921X_SGMII_CTRL, mask);
> +		if (res)
> +			return res;
> +
> +		mask = YT921X_XMII_CTRL_PORTn(port);
> +		res = yt921x_reg_clear_bits(priv, YT921X_XMII_CTRL, mask);
> +		if (res)
> +			return res;
> +
> +		mask = YT921X_SGMII_MODE_M;
> +		switch (interface) {
> +		case PHY_INTERFACE_MODE_SGMII:
> +			ctrl = YT921X_SGMII_MODE_SGMII_PHY;
> +			break;
> +		case PHY_INTERFACE_MODE_100BASEX:
> +			ctrl = YT921X_SGMII_MODE_100BASEX;
> +			break;
> +		case PHY_INTERFACE_MODE_1000BASEX:
> +			ctrl = YT921X_SGMII_MODE_1000BASEX;
> +			break;
> +		case PHY_INTERFACE_MODE_2500BASEX:
> +			ctrl = YT921X_SGMII_MODE_2500BASEX;
> +			break;
> +		default:
> +			WARN_ON(1);
> +			break;
> +		}

Hi David,

If the default case is reached above then ctrl is used uninitialised below.

Flagged by Clang 21.2.1

> +		res = yt921x_reg_update_bits(priv, YT921X_SGMIIn(port),
> +					     mask, ctrl);
> +		if (res)
> +			return res;
> +
> +		break;
> +	/* add XMII support here */
> +	default:
> +		WARN_ON(1);
> +		break;
> +	}
> +
> +	return 0;
> +}

...