Re: AW: AW: [PATCH 2/2] hwmon: (lm75) Support active-high alert polarity

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

On 5/1/26 13:42, markus.stockhausen@gmx.de wrote:
>> Von: Guenter Roeck <groeck7@gmail.com> Im Auftrag von Guenter Roeck
>> Gesendet: Freitag, 1. Mai 2026 22:14
>> Betreff: Re: AW: [PATCH 2/2] hwmon: (lm75) Support active-high alert polarity
>>   
>>> So this will need separate patches:
>>> 1) Fix set_mask and alert handling for AS6200 to be low active
>>>      and to report the alarm correctly even if it is high active
>>>      (xor config register bit 5 and 10 (translated to 2 and 13)
>>>      when reporting the alarm).
>>> 2) Fix lm75_write_config() to add set_mask to clr_mask to ensure
>>>      that the bits which are supposed to be set are actually set.
>>>
>>
>> Turns out the default value for AS6200 has more problems. It is set to
>> 0x94c0 which claims to be "8 sample/s, 4 CF, positive polarity".
>>
>> 0xc0 reflects the samples/s. So far so good. However, 0x94 is wrong.
>> It sets the single shot bit, effectively disabling the sensor, and
>> it does not set the CF bits as advertised. Please change the default
>> to 0x10c0 which reflects the intent more closely, except for the
>> negative polarity.
> 
> Understood. I still need advise about xor during alarm report.
> Do you talk about this code?
> 
>    case as6200:
>    case tmp112:
> -  *val = (regval >> 13) & 0x1;
> +  *val = ((regval >> 13) & 0x1) ^ 0x1;
> 
No, you'll need to xor bit 2 (the polarity bit) and 13 (the alert bit).

Something like
	alarm = !!(regval & BIT(13)) ^ !!(regval & BIT(2))

> Mabye totally stupid but this bug and the deep dive follow up
> hits my brain a little bit too hard.
> 
:-)

Cheers,
Guenter