Re: [PATCH v2 2/6] hwmon: (max6697) Drop platform data support

[Tzung-Bi Shih <tzungbi@kernel.org>]

On Wed, Jul 24, 2024 at 07:25:31AM -0700, Guenter Roeck wrote:
> On 7/24/24 06:03, Tzung-Bi Shih wrote:
> > On Tue, Jul 23, 2024 at 08:44:43AM -0700, Guenter Roeck wrote:
> > > +	if (data->type != max6581) {
> > > +		if (of_property_read_bool(node, "resistance-cancellation") &&
> > > +		    chip->valid_conf & MAX6697_CONF_RESISTANCE) {
> > > +			confreg |= MAX6697_CONF_RESISTANCE;
> > > +			factor = 1;
> > > +		}
> > > +	} else {
> > > +		if (of_property_read_u32(node, "resistance-cancellation", &vals[0])) {
> > > +			if (of_property_read_bool(node, "resistance-cancellation"))
> > > +				vals[0] = 0xfe;
> > > +			else
> > > +				vals[0] = 0;
> > > +		}
> > > +
> > > +		factor = hweight8(vals[0] & 0xfe);
> > 
> > It doesn't AND with 0xfe originally.
> > 
> 
> Yes, but the original code uses the value in
> 	factor += hweight8(pdata->resistance_cancellation >> 1);
> 	ret = i2c_smbus_write_byte_data(client, MAX6581_REG_RESISTANCE,
>                                         pdata->resistance_cancellation >> 1);
> which is effectively the same. I can't just use
> 	factor = hweight8(vals[0] >> 1);
> because, unlike resistance_cancellation, val[] is an u32 array which would
> not auto-mask the upper bits.

If you are worrying about:
* MSB, it should be fine as it should only prepend 0s for right shift on
  unsigned.
* BIT(8), other `val[0] >> 1` should also share the same concern.