Gmsl1 max9296: i2c read/write registers OK max9271: i2c read/write registers KO

Read write serializer gmsl1 failed with error -121

nvidia jetson xavier agx with the following configuration:
gmsl1: switch gmsl1 is correctly set on the board.
max9296: read/write registers OK
max9271: read/write registers KO

i2ctools detects the deserializer (i2c addr 0x48) and the serializer(0x40)

sudo i2cdetect -y -r 7
0 1 2 3 4 5 6 7 8 9 a b c d e f
00: – – – – – – – – – – – – –
10: – – – – – – – – – – – – – – – –
20: – – – – – – – – – – – – – – – –
30: – – – – – – – – – – – – – – – –
40: UU – – – – – – – UU – – – – – –
50: – – – – – – – – – – – – – – – –
60: – – – – – – – – – – – – – – – –
70: – UU – – – – – –

In the drivers:
read/write max9296 registers is OK
read max9271 registers is failed (error code -121) ?

Do we need to use the multiplexer to read / write the serializer ?
i2c-mux,deselect-on-exit;
reg_mux = <0x00>;
Best regards

Don’t need mux if the device slave address didn’t conflict.

Hello,
any idea about the code error -121 return by i2c_smbus_read_byte_data.

best regards

I would suggest to probe the i2c signal to check if device ack or not.