Re: [PATCH v5 0/3] hwmon: Add support for the LTC4283 Hot Swap Controller

["Nuno Sá" <noname.nuno@gmail.com>]

On Wed, 2026-01-28 at 10:22 -0800, Guenter Roeck wrote:
> On Wed, Jan 28, 2026 at 06:07:24PM +0000, Nuno Sá wrote:
> > > [ ... ]
> > > 
> > > > +static int ltc4283_read_power_word(const struct ltc4283_hwmon *st,
> > > > +				   u32 reg, long *val)
> > > > +{
> > > > +	u64 temp = (u64)LTC4283_ADC1_FS_uV * LTC4283_ADC2_FS_mV * DECA * MILLI;
> > > > +	unsigned int __raw;
> > > > +	int ret;
> > > > +
> > > > +	ret = regmap_read(st->map_word, reg, &__raw);
> > > > +	if (ret)
> > > > +		return ret;
> > > > +
> > > > +	/*
> > > > +	 * Power is given by:
> > > > +	 *     P = CODE(16b) * 32.768mV * 2.048V / (2^16 * Rsense)
> > > > +	 */
> > > > +	*val = DIV64_U64_ROUND_CLOSEST(temp * __raw, BIT_ULL(16) * st->rsense);
> > > 
> > > Does this overflow *val on 32-bit systems if the calculated power exceeds
> > > 2000 Watts (approx 2^31 microWatts)?  The intermediate calculation is
> > > u64, but the result is assigned to a signed long.
> > > 
> > 
> > I'll have to double check this one but IIRC 2000W is not a realistic value for
> > these applications. One thing that could overflow is power_max given that the default
> > register value is 0xff but we do write the proper max value depending on
> > rsense (I actually need to check how will this behave in case we use a default
> > rsense value - ie with no DT property).
> > 
> 
> I have been wondering if I should introduce a hwmon_power64 sensor type, similar to
> hwmon_energy64. WDYT ?
> 

No strong opinion. As I said, not sure if it's needed here but OTOH given that power is
microWatts I guess it's a matter of time. Anyways, if you do it, I might as well just play safe
and use it in here (and ltc4282 should also be converted - likely).

- Nuno Sá