> Plus "i2cdetect -r <num>" shows the device as UU for address 0x50, as
> usually happens with a driver is loaded.

Always. The address is blocked for userspace in any case.

> I thought that connected I2C devices always showed in i2cdetect output,
> whether they are declared in the device tree and have a driver or not.

This is a valid expectation. Since you used 'i2cdetect -r', it means
that the device does not react to the read_byte method. Very strange (if
not even against the specs). Did you try without '-r' to use
SMBUS_QUICK? What driver are we talking about anyhow?