Re: LM90 driver and ti tmp461 detection

[Guenter Roeck <linux@roeck-us.net>]

On 12/10/2015 04:08 AM, Andreas Werner wrote:
> Hi,
> i have a temperature sensor device named "TI TMP461" which is quite the
> same than the tmp451 which is already included in the lm90 driver.
>
> I just want to add the tmp461 to the driver but currently i have no way
> to differ between the tmp461 and tmp451.
>
> The main different is that the tmp461 address can be configured by to Pins
> whereas the tmp451 has a fixed address.
>
> The register layout is quite the same except that the tmp461 has one
> register more (0x16 Channel Enable Register).
>
> Every zero bit is the same for both bits, so we cannot use these bits for
> identification.
>
> Does anybody of you have a tmp451 to read out the register 0x16 (which is
> not implement but i expect a value). May be we can use this to
> identify the tmp461.
>

Here is a register dump.

00: 5d 69 00 04 08 bf 00 ff 53 00 00 00 00 00 00 00    ]i.???..S.......
10: a0 00 00 00 00 f0 00 00 00 a9 00 00 00 00 00 00    ?....?...?......
20: b8 0a 01 00 00 XX 00 00 00 00 0e 00 00 00 00 00    ???..X....?.....
30: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00    ................
40: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00    ................
50: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00    ................
60: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00    ................
70: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00    ................
80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00    ................
90: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00    ................
a0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00    ................
b0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00    ................
c0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00    ................
d0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00    ................
e0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00    ................
f0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 55 00    ..............U.

there is nothing to distinguish the two chips as far as I can see.
Is your system a devicetree system ? If so, you can just
provide a compatible statement such as
	compatible = "ti,tmp461", "ti,tmp451";
or simply instantiate the chip as tmp451.

Feel free to provide a patch adding '{ "tmp461", tmp451 },'
to lm90_id as well as the necessary documentation, but I don't
think there is anything we can do to detect the chip.

On the other side, I am a bit concerned that the chip detection doesn't
work well, since the chip ID register is really unsupported and just happens
to return 0 for both chips. I wonder if there are other TI chips which may
be mis-detected as TMP451.

Thanks,
Guenter