# Re: \[PATCH v2 net-next 02/15\] net: mdio: add driver for NXP SJA1110 100BASE-T1 embedded PHYs

- From: Vladimir Oltean \<vladimir.oltean@nxp.com\>
- Date: 2026-01-22 12:47:14 
- List: netdev
- Page: https://ratatoskr.run/netdev/2026/01/3382169
- Thread: https://ratatoskr.run/netdev/2026/01/3381930/t.md

```text
On Thu, Jan 22, 2026 at 02:12:21PM +0200, Andy Shevchenko wrote:
> On Thu, Jan 22, 2026 at 12:56:41PM +0200, Vladimir Oltean wrote:
> > This driver is the standalone variant of drivers/net/dsa/sja1105/sja1105_mdio.c.
> > In terms of differences:
> > 
> > - this one uses regmaps provided by the parent as a method to abstract
> >   away the sja1105_xfer_u32() calls for register access
> > - the driver prefix has been changed from sja1105 to sja1110 (this MDIO
> >   controller is not present on the older SJA1105 family)
> > - in the sja1105 driver, each memory word has 32 bits, so addresses as
> >   seen by regmap need to be multiplied by 4. This affects what
> >   sja1110_base_t1_encode_addr() returns, and is different compared to
> >   sja1105_base_t1_encode_addr().
> 
> ...
> 
> > +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.

> > +	err = regmap_read(regmap, priv->base + addr, &val);
> > +	if (err)
> > +		return err;
> > +
> > +	return val & 0xffff;
> 
> lower_16_bits() from wordpart.h?

Ok, let's say so.

> > +}
> 
> ...
> 
> > +static int sja1110_base_t1_mdio_read_c45(struct mii_bus *bus, int phy,
> > +					 int mmd, 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_C45_ADDR, mmd);
> > +	err = regmap_write(regmap, priv->base + addr, reg);
> > +	if (err)
> > +		return err;
> > +
> > +	addr = sja1110_base_t1_encode_addr(phy, SJA1110_C45_DATA, mmd);
> > +	err = regmap_read(regmap, priv->base + addr, &val);
> > +	if (err)
> > +		return err;
> > +
> > +	return val & 0xffff;
> 
> Ditto.
> 
> > +}
> 
> ...
> 
> > +static int sja1110_base_t1_mdio_write_c22(struct mii_bus *bus, int phy, int reg,
> > +					  u16 val)
> > +{
> > +	struct sja1110_base_t1_private *priv = bus->priv;
> > +	struct regmap *regmap = priv->regmap;
> > +	unsigned int addr;
> > +
> > +	addr = sja1110_base_t1_encode_addr(phy, SJA1110_C22, reg & 0x1f);
> > +	return regmap_write(regmap, priv->base + addr, val & 0xffff);
> 
> val is already u16.

Ok.

> > +}
> 
> ...
> 
> > +static int sja1110_base_t1_mdio_write_c45(struct mii_bus *bus, int phy,
> > +					  int mmd, int reg, u16 val)
> > +{
> > +	struct sja1110_base_t1_private *priv = bus->priv;
> > +	struct regmap *regmap = priv->regmap;
> > +	unsigned int addr;
> > +	int err;
> > +
> > +	addr = sja1110_base_t1_encode_addr(phy, SJA1110_C45_ADDR, mmd);
> > +	err = regmap_write(regmap, priv->base + addr, reg);
> > +	if (err)
> > +		return err;
> > +
> > +	addr = sja1110_base_t1_encode_addr(phy, SJA1110_C45_DATA, mmd);
> > +	return regmap_write(regmap, priv->base + addr, val & 0xffff);
> 
> Ditto.
> 
> > +}
> 
> ...
> 
> > +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;
> 
> > +	if (!dev->of_node || !dev->parent)
> 
> Can we avoid dereferencing? And perhaps dev_fwnode(dev)?

Avoid dereferencing what?

> > +		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?

> > +	if (err)
> > +		goto err_free_bus;
> > +
> > +	priv->bus = bus;
> > +	platform_set_drvdata(pdev, priv);
> > +
> > +	return 0;
> > +
> > +err_free_bus:
> > +	mdiobus_free(bus);
> > +
> > +	return err;
> > +}
> 
> ...
> 
> > +static const struct of_device_id sja1110_base_t1_mdio_match[] = {
> > +	{ .compatible = "nxp,sja1110-base-t1-mdio", },
> 
> Inner comma is redundant.

Ok.

> > +	{},
> 
> Terminator is terminator, trailing comma is confusing here.

Ok.

> > +};
> 
> ...
> 
> > +static struct platform_driver sja1110_base_t1_mdio_driver = {
> > +	.probe = sja1110_base_t1_mdio_probe,
> > +	.remove = sja1110_base_t1_mdio_remove,
> > +	.driver = {
> > +		.name = "sja1110-base-t1-mdio",
> > +		.of_match_table = sja1110_base_t1_mdio_match,
> > +	},
> > +};
> 
> > +
> 
> Redundant blank line.

Ok.

> > +module_platform_driver(sja1110_base_t1_mdio_driver);
> 
> -- 
> With Best Regards,
> Andy Shevchenko
> 
>
```