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Message-ID: <20260122124708.pxckp6vgi2rvagmm@skbuf>
Date: Thu, 22 Jan 2026 14:47:08 +0200
From: Vladimir Oltean <vladimir.oltean@....com>
To: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc: netdev@...r.kernel.org, Andrew Lunn <andrew@...n.ch>,
Heiner Kallweit <hkallweit1@...il.com>,
Russell King <linux@...linux.org.uk>,
"David S. Miller" <davem@...emloft.net>,
Eric Dumazet <edumazet@...gle.com>,
Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
linux-kernel@...r.kernel.org,
Herve Codina <herve.codina@...tlin.com>,
Mark Brown <broonie@...nel.org>,
Serge Semin <fancer.lancer@...il.com>,
Maxime Chevallier <maxime.chevallier@...tlin.com>,
Lee Jones <lee@...nel.org>, Rob Herring <robh@...nel.org>,
Krzysztof Kozlowski <krzk+dt@...nel.org>,
Conor Dooley <conor+dt@...nel.org>, devicetree@...r.kernel.org,
Choong Yong Liang <yong.liang.choong@...ux.intel.com>,
Jiawen Wu <jiawenwu@...stnetic.com>
Subject: Re: [PATCH v2 net-next 02/15] net: mdio: add driver for NXP SJA1110
100BASE-T1 embedded PHYs
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
>
>
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