Hi Hans,

> +out_log:
> +	dev_dbg(adap->dev.parent, "RD[%d]:%*phN\n", msg->len, msg->len, msg->buf);

I think this...

> +
> +	return 0;
> +}
> +
> +static int usbio_i2c_write(struct i2c_adapter *adap, struct i2c_msg *msg)
> +{
> +	struct usbio_i2c *i2c = i2c_get_adapdata(adap);
> +	u16 txchunk = i2c->txbuf_len - I2C_RW_OVERHEAD;
> +	struct usbio_i2c_rw *wbuf = i2c->rwbuf;
> +	int ret;
> +
> +	dev_dbg(adap->dev.parent, "WR[%d]:%*phN\n", msg->len, msg->len, msg->buf);

... and this dbg can go. The tracepoints we have should do?

> +static u32 usbio_i2c_func(struct i2c_adapter *adap)
> +{
> +	return I2C_FUNC_I2C | I2C_FUNC_10BIT_ADDR | I2C_FUNC_SMBUS_EMUL;
> +}

How did you test 10 bit addresses? I have never seen them in the wild?

Did you also check SMBUS_QUICK? 'i2cdetect' uses it by default.

Does the underlying USBIO driver use usb_control_msg? If so, we need to
disable zero length read messages. See [1] for a reference.

Rest looks good to me!

[1] https://lore.kernel.org/all/20250522064234.3721-2-wsa+renesas@sang-engineering.com/