net: dsa: mxl-gsw1xx: validate chip ID

No check for actually present hardware is being performed in the probe
function of the mxl-gsw1xx switch driver. So even if the switch isn't
present at the configured MDIO bus address the driver wrongly tells the
user that a "GSWIP version 0 mod 0" was found, outputting errors about
PHY capabilities not matching.

Read and validate the chip MANU_ID and PNUM_ID registers and output
information while probing, but return an error and abort probing in case
the hardware is not actually present.

Signed-off-by: Daniel Golle <daniel@makrotopia.org>
Link: https://patch.msgid.link/3194d3d3bb0b51f08755d392e1fdf7bb6dc49608.1769916962.git.daniel@makrotopia.org
Reviewed-by: Vladimir Oltean <olteanv@gmail.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

Author: dangowrt

drivers/net/dsa/lantiq/mxl-gsw1xx.c

@@ -688,7 +688,9 @@ static int gsw1xx_probe(struct mdio_device *mdiodev)
 {
 	struct device *dev = &mdiodev->dev;
 	struct gsw1xx_priv *priv;
-	u32 version;
+	u32 version, val;
+	u8 shellver;
+	u16 pnum;
 	int ret;
 
 	priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
@@ -736,6 +738,27 @@ static int gsw1xx_probe(struct mdio_device *mdiodev)
 	if (IS_ERR(priv->shell))
 		return PTR_ERR(priv->shell);
 
+	ret = regmap_read(priv->shell, GSW1XX_SHELL_MANU_ID, &val);
+	if (ret < 0)
+		return ret;
+
+	/* validate chip ID */
+	if (FIELD_GET(GSW1XX_SHELL_MANU_ID_FIX1, val) != 1)
+		return -ENODEV;
+
+	if (FIELD_GET(GSW1XX_SHELL_MANU_ID_MANID, val) !=
+	    GSW1XX_SHELL_MANU_ID_MANID_VAL)
+		return -ENODEV;
+
+	pnum = FIELD_GET(GSW1XX_SHELL_MANU_ID_PNUML, val);
+
+	ret = regmap_read(priv->shell, GSW1XX_SHELL_PNUM_ID, &val);
+	if (ret < 0)
+		return ret;
+
+	pnum |= FIELD_GET(GSW1XX_SHELL_PNUM_ID_PNUMM, val) << 4;
+	shellver = FIELD_GET(GSW1XX_SHELL_PNUM_ID_VER, val);
+
 	ret = gsw1xx_serdes_pcs_init(priv);
 	if (ret < 0)
 		return ret;
@@ -756,6 +779,8 @@ static int gsw1xx_probe(struct mdio_device *mdiodev)
 	if (ret)
 		return ret;
 
+	dev_info(dev, "standalone switch part number 0x%x v1.%u\n", pnum, shellver);
+
 	dev_set_drvdata(dev, &priv->gswip);
 
 	return 0;

drivers/net/dsa/lantiq/mxl-gsw1xx.h

@@ -110,6 +110,15 @@
 #define GSW1XX_SHELL_BASE			0xfa00
 #define  GSW1XX_SHELL_RST_REQ			0x01
 #define   GSW1XX_RST_REQ_SGMII_SHELL		BIT(5)
+#define  GSW1XX_SHELL_MANU_ID			0x10
+#define   GSW1XX_SHELL_MANU_ID_PNUML		GENMASK(15, 12)
+#define   GSW1XX_SHELL_MANU_ID_MANID		GENMASK(11, 1)
+#define    GSW1XX_SHELL_MANU_ID_MANID_VAL	0x389
+#define   GSW1XX_SHELL_MANU_ID_FIX1		BIT(0)
+#define  GSW1XX_SHELL_PNUM_ID			0x11
+#define   GSW1XX_SHELL_PNUM_ID_VER		GENMASK(15, 12)
+#define   GSW1XX_SHELL_PNUM_ID_PNUMM		GENMASK(11, 0)
+
 /* RGMII PAD Slew Control Register */
 #define  GSW1XX_SHELL_RGMII_SLEW_CFG		0x78
 #define   RGMII_SLEW_CFG_DRV_TXC		BIT(2)