RE: [PATCH v3 2/2] hwmon: (pmbus/max20830) add driver for max20830

[Torreno, Alexis Czezar]

> 
> On Fri, Apr 17, 2026 at 04:27:14PM +0800, Alexis Czezar Torreno wrote:
> > Add support for MAX20830 step-down DC-DC switching regulator with
> > PMBus interface. It allows monitoring of input/output voltage, output
> > current and temperature through the PMBus serial interface.
> >
> > Signed-off-by: Alexis Czezar Torreno <alexisczezar.torreno@xxxxxxxxxx>
> > ---
> ...
> > +
> > +	/*
> > +	 * Use i2c_smbus_read_i2c_block_data() instead of
> > +	 * i2c_smbus_read_block_data() to support I2C controllers
> > +	 * which do not support SMBus block reads.
> > +	 */
> > +	ret = i2c_smbus_read_i2c_block_data(client, PMBUS_IC_DEVICE_ID,
> > +					    I2C_SMBUS_BLOCK_MAX, buf);
> > +	if (ret < 0)
> > +		return dev_err_probe(&client->dev, ret,
> > +				     "Failed to read IC_DEVICE_ID\n");
> > +
> > +	/* First byte is the block length (including itself). */
> > +	len = buf[0];
> > +	if (len != 9 || ret < len)
> > +		return dev_err_probe(&client->dev, -ENODEV,
> > +				     "IC_DEVICE_ID length mismatch: reported
> %u, read %d\n",
> > +				     len, ret);
> > +
> > +	/* Data is at buf[1..8], so null terminator goes at buf[9]. */
> 
> I ended up checking the kernel code. As it turns out,
> i2c_smbus_read_i2c_block_data does _not_ return the length in byte 0.
> It returns the first byte of the actual data, and the length as return value. See
> i2c_smbus_read_i2c_block_data() in drivers/i2c/i2c-core-smbus.c.
> 
> So this can not work as written. Something like
> 
>         if (i2c_check_functionality(client->adapter,
> I2C_FUNC_SMBUS_BLOCK_DATA))
>                 ret = i2c_smbus_read_block_data(client, PMBUS_IC_DEVICE_ID,
> data_buf);
>         else
>                 ret = i2c_smbus_read_i2c_block_data(client, PMBUS_IC_DEVICE_ID,
> 						    I2C_SMBUS_BLOCK_MAX,
> buf);
> 
> should do, assuming that support for I2C_FUNC_SMBUS_BLOCK_DATA
> and/or I2C_FUNC_SMBUS_READ_I2C_BLOCK was checked before.
> 

Oh, ok will check this difference out. Thanks