linux-kernel - Re: [PATCHv1 06/11] power: supply: generic-adc-battery: drop charge now support

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Message-ID: <CACRpkdaHKZjkvZYM6GAnzXeRgfqFWE1aGMEqkN1HQ-3TX-DjtA@mail.gmail.com>
Date:   Mon, 13 Mar 2023 09:33:16 +0100
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Matti Vaittinen <mazziesaccount@...il.com>
Cc:     Sebastian Reichel <sre@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        devicetree@...r.kernel.org
Subject: Re: [PATCHv1 06/11] power: supply: generic-adc-battery: drop charge
 now support

On Mon, Mar 13, 2023 at 8:49 AM Matti Vaittinen
<mazziesaccount@...il.com> wrote:
> On 3/10/23 10:29, Linus Walleij wrote:
> > On Thu, Mar 9, 2023 at 11:50 PM Sebastian Reichel <sre@...nel.org> wrote:
> >
> >> Drop CHARGE_NOW support, which requires a platform specific
> >> calculation method.
> >>
> >> Signed-off-by: Sebastian Reichel <sre@...nel.org>
> >
> > I agree. If we want to support this, we should use the generic
> > methods with interpolation tables defined in DT as well, and it also
> > ideally requires load compensated resistance calculation to figure
> > out Ri so this can bring any kind of reasonable precision.
>
> I guess you have your reasons, besides you have far better insight to
> things than I do - hence I am not really objecting this - just asking a
> question ;)
>
> Do we have generic facilities of computing this based on the DT tables /
> Ri in place(?)

Not yet, for the Samsung batteries I used a static look-up table
derived from the compatible string for calculating Ri from VBAT
and from that calculate the capacity from estimated open
circuit voltage, see
drivers/power/supply/samsung-sdi-battery.c

> I guess that we do need/see platform specific
> implementations as long as there is no generic "de-facto" way of doing
> this available...

The method I used with Samsung batteries is fine as long as all you
need to know to know everything about a battery is the compatible
string. Pretty much any Lion battery with a clearly defined product
name can be done this way.

The only reason to put the interpolation tables into the device
tree would be to support any random battery, such as one
that you do not know the model or this can change.

I am however mildly sceptic about adding that: if you know the
VBAT-to-Ri and OCV-to-capacity tables, you must have a
datasheet, and then you know the name of the battery product
and hence you know the right compatible string...

I think the right way to handle any capacity curves for any battery
would be to create static data like I did for the Samsung batteries.

Yours,
Linus Walleij