Re: [PATCH v2 2/4] hwmon: (pmbus/ltc2978) Add support for LT7175 and LT7176P

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential
issue to consider:
- [Medium] hwmon: (pmbus/ltc2978) IEEE-754 peaks compared as LINEAR11 in
  ltc_get_max()
--

commit 201c09e7f06ead2d62e423cba00a536dde067159
Author: Christopher de Guzman <christopher.deguzman@analog.com>

hwmon: (pmbus/ltc2978) Add support for LT7175 and LT7176P

This commit adds support for the LT7175 and LT7176P PMBus buck regulators
and matches PMBUS_IC_DEVICE_ID strings against ltc2978_id[] for the LT7170
family.

> diff --git a/drivers/hwmon/pmbus/ltc2978.c b/drivers/hwmon/pmbus/ltc2978.c
> index aea7b6c93e74b..888db3213a01e 100644
> --- a/drivers/hwmon/pmbus/ltc2978.c
> +++ b/drivers/hwmon/pmbus/ltc2978.c
[ ... ]
> @@ -762,6 +763,8 @@ static int ltc2978_probe(struct i2c_client *client)
>  	switch (data->id) {
>  	case lt7170:
>  	case lt7171:
> +	case lt7175:
> +	case lt7176p:
>  		data->features |= FEAT_CLEAR_PEAKS | FEAT_NEEDS_POLLING;
>  		info->read_word_data = ltc3883_read_word_data;
>  		info->pages = LTC3883_NUM_PAGES;

[Severity: Medium]
Does routing lt7175 and lt7176p (along with lt7170 and lt7171) through
ltc3883_read_word_data() corrupt peak readings when the data format is
ieee754?

ltc3883_read_word_data() -> ltc3880_read_word_data() ->
ltc2978_read_word_data_common() reads PMBUS_VIRT_READ_IOUT_MAX,
PMBUS_VIRT_READ_VIN_MAX, and PMBUS_VIRT_READ_TEMP_MAX via ltc_get_max():

drivers/hwmon/pmbus/ltc2978.c:ltc_get_max() {
    ...
	ret = ltc_read_word_data(client, page, 0xff, reg);
	if (ret >= 0) {
		if (lin11_to_val(ret) > lin11_to_val(*pmax))
			*pmax = ret;
		ret = *pmax;
	}
    ...
}

lin11_to_val() treats bit 10 as the two's-complement mantissa sign bit.
In IEEE-754 binary16, bit 10 is the least-significant bit of the biased
exponent, so positive values with an odd biased exponent (such as
temperatures in [64, 128) C or voltages in [16, 32) V) decode as negative
and are discarded in favor of smaller readings with an even biased
exponent.

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261110-upstream-lt7175-lt7176p-v2-0-dd60d28383bf@analog.com?part=2