Re: [PATCH v2 9/9] hwmon: adm1275: Support ROHM BD12790

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Low] The mathematical formula documented in the comment for computing the power coefficient contradicts the actual mathematically correct implementation in the code.
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commit 7dff114234776369f1046124af65696c292fcd41
Author: Matti Vaittinen <mazziesaccount@gmail.com>

hwmon: adm1275: Support ROHM BD12790

This commit adds support for the ROHM BD12790 hot-swap controller to the
adm1275 driver. It introduces a dedicated coefficient table for the new
device based on its voltage and current-sense ranges.

> diff --git a/drivers/hwmon/pmbus/adm1275.c b/drivers/hwmon/pmbus/adm1275.c
> index 81c50fab7687b..406b448523769 100644
> --- a/drivers/hwmon/pmbus/adm1275.c
> +++ b/drivers/hwmon/pmbus/adm1275.c

[ ... ]

> @@ -136,6 +136,30 @@ static const struct coefficients adm1272_coefficients[] = {
>  
>  };
>  
> +/*
> + * BD12790 coefficients derived from preliminary datasheet, Table 1 (p.18)
> + * and the PMBus direct-format relationship X = (Y * 10^(-R) - b) / m.
> + *
> + * Voltage: V[V] = 14.77e-3 * code (60V) / 24.62e-3 * code (100V)
> + *   -> m = 6770, R=-2 / m = 4062, R=-2
> + * Current: code = I[A] * RS * 132802.1 + 2048 (15mV) / * 66401.06 + 2048 (30mV)
> + *   -> m = 1328, b = 2048 * 10^(-R) = 20480, R=-1 / m = 664, same b and R
> + * Power: code = k * RS * PIN, k = 35119.94 / 17559.97 / 21071.44 / 10535.72
> + *   -> m = round(k / 10^(-3-R)), R=-2 for 60V/15mV, R=-3 for the other three

[Severity: Low]
This isn't a bug, but does the formula in this comment correctly document
how the power coefficients are calculated?

If we evaluate m = round(k / 10^(-3-R)) for a value of R=-2 and k=35119.94,
it yields 351199.4. However, the actual code below correctly implements the
value as 3512, which implies the formula should use multiplication rather
than division.

> + * Temperature: code = 4.2 * T + 3188 -> m = 42, b = 3188 * 10 = 31880, R=-1
> + */
> +static const struct coefficients bd12790_coefficients[] = {
> +	[0] = { 6770, 0, -2 },		/* voltage, vrange 60V */
> +	[1] = { 4062, 0, -2 },		/* voltage, vrange 100V */
> +	[2] = { 1328, 20480, -1 },	/* current, vsense range 15mV */
> +	[3] = { 664, 20480, -1 },	/* current, vsense range 30mV */
> +	[4] = { 3512, 0, -2 },		/* power, vrange 60V, irange 15mV */
> +	[5] = { 21071, 0, -3 },		/* power, vrange 100V, irange 15mV */
> +	[6] = { 17560, 0, -3 },		/* power, vrange 60V, irange 30mV */
> +	[7] = { 10536, 0, -3 },		/* power, vrange 100V, irange 30mV */
> +	[8] = { 42, 31880, -1 },	/* temperature */
> +};
> +

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Sashiko AI review · https://sashiko.dev/#/patchset/cover.1782458224.git.mazziesaccount@gmail.com?part=9