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

[Guenter Roeck]

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@xxxxxxxxxxx>
> >
> > 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@xxxxxxxxxxx>
> > ---
>
> 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@xxxxxxxxxx>
>
> >   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