On Thu, Jan 22, 2026 at 02:47:08PM +0200, Vladimir Oltean wrote:

On Thu, Jan 22, 2026 at 02:12:21PM +0200, Andy Shevchenko wrote:

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On Thu, Jan 22, 2026 at 12:56:41PM +0200, Vladimir Oltean wrote:

...

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+static int sja1110_base_t1_mdio_read_c22(struct mii_bus *bus, int phy, int reg)
+{
+	struct sja1110_base_t1_private *priv = bus->priv;
+	struct regmap *regmap = priv->regmap;
+	unsigned int addr, val;
+	int err;
+
+	addr = sja1110_base_t1_encode_addr(phy, SJA1110_C22, reg & 0x1f);

GENMASK() ? Or do you have already a defined mask for this?

Hmm, I can't find a definition for this. In the MDIO world it is
"well known" that clause 22 offers a 5-bit register address space.
So the 0x1f number doesn't seem too magical to me.

But I think my assumptions date since before the MDIO bus API was split
between separate clause 22 and clause 45 reads/writes. I don't know
whether masking reg & 0x1f is the best practice. I'm surprised that
__mdiobus_read() doesn't enforce a limit on "regnum", and I don't see
other MDIO bus drivers explicitly C22 registers >= 32. I really don't
know what is the best practice.

Me neither. At bare minimum to check / perform two things:
- make sure this approach is consistent across the kernel
- define the magic with meaningful name

Maybe (assuming second one is done) fix the rest in the future
via some helper function?

...

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+static int sja1110_base_t1_mdio_probe(struct platform_device *pdev)
+{
+	struct sja1110_base_t1_private *priv;
+	struct device *dev = &pdev->dev;
+	struct regmap *regmap;
+	struct resource *res;
+	struct mii_bus *bus;
+	int err;

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+	if (!dev->of_node || !dev->parent)

Can we avoid dereferencing? And perhaps dev_fwnode(dev)?

Avoid dereferencing what?

of_node

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+		return -ENODEV;
+
+	regmap = dev_get_regmap(dev->parent, NULL);
+	if (!regmap)
+		return -ENODEV;
+
+	bus = mdiobus_alloc_size(sizeof(*priv));
+	if (!bus)
+		return -ENOMEM;
+
+	bus->name = "SJA1110 100base-T1 MDIO bus";
+	snprintf(bus->id, MII_BUS_ID_SIZE, "%s", dev_name(dev));
+	bus->read = sja1110_base_t1_mdio_read_c22;
+	bus->write = sja1110_base_t1_mdio_write_c22;
+	bus->read_c45 = sja1110_base_t1_mdio_read_c45;
+	bus->write_c45 = sja1110_base_t1_mdio_write_c45;
+	bus->parent = dev;
+	priv = bus->priv;
+	priv->regmap = regmap;
+
+	res = platform_get_resource(pdev, IORESOURCE_REG, 0);
+	if (res)
+		priv->base = res->start;
+
+	err = of_mdiobus_register(bus, dev->of_node);

Why would I use dev_fwnode() if I need to pass it as OF to
of_mdiobus_register() here?

dev_of_node() then. Wondering if we can use fwnode_mdiobus_register_phy() here
(I remember that OF/fwnode code in MDIO/PHY is not trivial, but I don't know
 all the details).

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+	if (err)
+		goto err_free_bus;
+
+	priv->bus = bus;
+	platform_set_drvdata(pdev, priv);
+
+	return 0;
+
+err_free_bus:
+	mdiobus_free(bus);
+
+	return err;
+}

-- 
With Best Regards,
Andy Shevchenko