Re: [PATCH] hwmon: adm1177: fix sysfs ABI violation and current unit conversion

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

On 3/25/26 03:37, Nuno Sá wrote:
> On Tue, 2026-03-24 at 18:22 +0000, Pradhan, Sanman wrote:
>> From: Sanman Pradhan <psanman@juniper.net>
>>
>> The adm1177 driver exposes the current alert threshold using
>> hwmon_curr_max_alarm. Per the hwmon sysfs ABI, *_alarm attributes
>> are read-only status flags; the writable threshold should use
>> hwmon_curr_max instead.
>>
>> Additionally, the threshold is stored internally in microamps
>> (alert_threshold_ua) but the ABI requires milliamps for currN_max.
>> Convert appropriately on both the read and write paths, and
>> propagate the return value of adm1177_write_alert_thr() which was
>> previously discarded.
>>
>> Clamp write values to the range the hardware can represent rather
>> than rejecting out-of-range input, and use DIV_ROUND_CLOSEST on the
>> read path to minimise rounding error during the uA-to-mA conversion.
>>
>> Fixes: 09b08ac9e8d5 ("hwmon: (adm1177) Add ADM1177 Hot Swap Controller and Digital Power Monitor
>> driver")
>> Signed-off-by: Sanman Pradhan <psanman@juniper.net>
>> ---
> 
> For the AI comment, typically these applications don't go to ohms for rsense so, in practice, it

Limiting rsense to a reasonable value (1 Ohm might do)might just be good enough.
That is really unrelated to this change, so it should be a separate patch.

> might be that we never get he overflow. But I would still play safe given it's so trivial. I also
> see you only replace hwmon_curr_max_alarm with hwmon_curr_max. It would be nicer to first fix ABI
> and then support hwmon_curr_max_alarm (properly). Though might be a big ask if you don't have HW to
> test it. Anyways, after AI feedback addressed:

Ah yes, good point. The chip _does_ support actual alerts, so that would be desirable.
However, that should also be a separate patch and, yes, it would be better to have an
actual chip at hand to make sure that it works as intended.

I'll apply this patch as-is.

Thanks,
Guenter

> 
> Acked-by: Nuno Sá <nuno.sa@analog.com>
> 
>>   drivers/hwmon/adm1177.c | 16 +++++++++-------
>>   1 file changed, 9 insertions(+), 7 deletions(-)
>>
>> diff --git a/drivers/hwmon/adm1177.c b/drivers/hwmon/adm1177.c
>> index 8b2c965480e3f..8742b8b5314b6 100644
>> --- a/drivers/hwmon/adm1177.c
>> +++ b/drivers/hwmon/adm1177.c
>> @@ -10,6 +10,7 @@
>>   #include <linux/hwmon.h>
>>   #include <linux/i2c.h>
>>   #include <linux/init.h>
>> +#include <linux/minmax.h>
>>   #include <linux/module.h>
>>   #include <linux/regulator/consumer.h>
>>   
>> @@ -91,8 +92,8 @@ static int adm1177_read(struct device *dev, enum hwmon_sensor_types type,
>>   			*val = div_u64((105840000ull * dummy),
>>   				       4096 * st->r_sense_uohm);
>>   			return 0;
>> -		case hwmon_curr_max_alarm:
>> -			*val = st->alert_threshold_ua;
>> +		case hwmon_curr_max:
>> +			*val = DIV_ROUND_CLOSEST(st->alert_threshold_ua, 1000);
>>   			return 0;
>>   		default:
>>   			return -EOPNOTSUPP;
>> @@ -126,9 +127,10 @@ static int adm1177_write(struct device *dev, enum hwmon_sensor_types type,
>>   	switch (type) {
>>   	case hwmon_curr:
>>   		switch (attr) {
>> -		case hwmon_curr_max_alarm:
>> -			adm1177_write_alert_thr(st, val);
>> -			return 0;
>> +		case hwmon_curr_max:
>> +			val = clamp_val(val, 0,
>> +					div_u64(105840000ULL, st->r_sense_uohm));
>> +			return adm1177_write_alert_thr(st, val * 1000);
>>   		default:
>>   			return -EOPNOTSUPP;
>>   		}
>> @@ -156,7 +158,7 @@ static umode_t adm1177_is_visible(const void *data,
>>   			if (st->r_sense_uohm)
>>   				return 0444;
>>   			return 0;
>> -		case hwmon_curr_max_alarm:
>> +		case hwmon_curr_max:
>>   			if (st->r_sense_uohm)
>>   				return 0644;
>>   			return 0;
>> @@ -170,7 +172,7 @@ static umode_t adm1177_is_visible(const void *data,
>>   
>>   static const struct hwmon_channel_info * const adm1177_info[] = {
>>   	HWMON_CHANNEL_INFO(curr,
>> -			   HWMON_C_INPUT | HWMON_C_MAX_ALARM),
>> +			   HWMON_C_INPUT | HWMON_C_MAX),
>>   	HWMON_CHANNEL_INFO(in,
>>   			   HWMON_I_INPUT),
>>   	NULL