Re: [RFC PATCH v2 1/6] power: supply: add cap2ocv batinfo helper

[Linus Walleij <linus.walleij@linaro.org>]

On Fri, Dec 4, 2020 at 1:41 PM Matti Vaittinen
<matti.vaittinen@fi.rohmeurope.com> wrote:

> The power-supply core supports concept of OCV (Open Circuit Voltage) =>
> SOC (State Of Charge) conversion tables. Usually these tables are used
> to estimate SOC based on OCV. Some systems use so called "Zero Adjust"
> where at the near end-of-battery condition the SOC from coulomb counter
> is used to retrieve the OCV - and OCV and VSYS difference is used to
> re-estimate the battery capacity.
>
> Add helper to do look-up the other-way around and also get the OCV
> based on SOC
>
> Signed-off-by: Matti Vaittinen <matti.vaittinen@fi.rohmeurope.com>

Overall a good idea!

> +/**
> + * power_supply_cap2ocv_simple() - find the battery OCV by capacity
> + * @table: Pointer to battery OCV/CAP lookup table
> + * @table_len: OCV/CAP table length
> + * @cap: Current cap value
> + *
> + * This helper function is used to look up battery OCV according to
> + * current capacity value from one OCV table, and the OCV table must be ordered
> + * descending.
> + *
> + * Return: the battery OCV.
> + */

Spell out the abbreviations in the kerneldoc and not just the commit.
These will be read much more than the commit message so I would
move all the excellent info in the commit message into the kerneldoc and
diet the commit message instead.

> +int power_supply_cap2ocv_simple(struct power_supply_battery_ocv_table *table,
> +                               int table_len, int cap)
> +{
> +       int i, ocv, tmp;
> +
> +       for (i = 0; i < table_len; i++)
> +               if (cap > table[i].capacity)
> +                       break;
> +
> +       if (i > 0 && i < table_len) {
> +               tmp = (table[i - 1].ocv - table[i].ocv) *
> +                     (cap - table[i].capacity);
> +
> +               tmp /= table[i - 1].capacity - table[i].capacity;
> +               ocv = tmp + table[i].ocv;

This is some linear interpolation right? It's not immediately evident so insert
some comment about what is going on.

>  /**
>   * power_supply_ocv2cap_simple() - find the battery capacity
>   * @table: Pointer to battery OCV lookup table
> @@ -847,6 +884,20 @@ power_supply_find_ocv2cap_table(struct power_supply_battery_info *info,

I suspect this kerneldoc could be improved in the process as well.

Yours,
Linus Walleij