linux-kernel - Re: [PATCH v1 4/4] power: max17040: get thermal data from adc if available

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Date:   Wed, 8 Mar 2023 11:23:27 +0200
From:   Svyatoslav Ryhel <clamor95@...il.com>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
Cc:     Iskren Chernev <me@...ren.info>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Matheus Castello <matheus@...tello.eng.br>,
        Sebastian Reichel <sre@...nel.org>,
        Rob Herring <robh+dt@...nel.org>, linux-pm@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 4/4] power: max17040: get thermal data from adc if available

ср, 8 бер. 2023 р. о 11:08 Krzysztof Kozlowski
<krzysztof.kozlowski@...aro.org> пише:
>
> On 08/03/2023 09:44, Svyatoslav Ryhel wrote:
> > Since fuel gauge does not support thermal monitoring,
> > some vendors may couple this fuel gauge with thermal/adc
> > sensor to monitor battery cell exact temperature.
> >
> > Add this feature by adding optional iio thermal channel.
> >
> > Signed-off-by: Svyatoslav Ryhel <clamor95@...il.com>
> > ---
> >  drivers/power/supply/max17040_battery.c | 24 ++++++++++++++++++++++++
> >  1 file changed, 24 insertions(+)
> >
> > diff --git a/drivers/power/supply/max17040_battery.c b/drivers/power/supply/max17040_battery.c
> > index 6dfce7b1309e..8c743c26dc6e 100644
> > --- a/drivers/power/supply/max17040_battery.c
> > +++ b/drivers/power/supply/max17040_battery.c
> > @@ -18,6 +18,7 @@
> >  #include <linux/of_device.h>
> >  #include <linux/regmap.h>
> >  #include <linux/slab.h>
> > +#include <linux/iio/consumer.h>
> >
> >  #define MAX17040_VCELL       0x02
> >  #define MAX17040_SOC 0x04
> > @@ -143,6 +144,7 @@ struct max17040_chip {
> >       struct power_supply             *battery;
> >       struct power_supply_battery_info        *batt_info;
> >       struct chip_data                data;
> > +     struct iio_channel              *channel_temp;
> >
> >       /* battery capacity */
> >       int soc;
> > @@ -416,6 +418,11 @@ static int max17040_get_property(struct power_supply *psy,
> >       case POWER_SUPPLY_PROP_CHARGE_FULL_DESIGN:
> >               val->intval = chip->batt_info->charge_full_design_uah;
> >               break;
> > +     case POWER_SUPPLY_PROP_TEMP:
> > +             iio_read_channel_raw(chip->channel_temp,
> > +                                  &val->intval);
> > +             val->intval *= 10;
>
> I am not convinced this is needed at all. You basically chain two
> subsystems only to report to user-space via power supply, but it is
> already reported via IIO. I would understand it if you use the value for
> something, e.g. control the charger. Here, it's just feeding different
> user-space interface. Therefore:
> 1. IO channels are not a hardware property of the fuel gauge,
> 2. I have doubts this should be even exposed via power supply interface.
>

I can assure you that this is only the beginning of weird vendor solutions
I have discovered. Nonetheless, max17040 has no battery temp property,
this means in case I have a critical battery overheating, userspace
will tell me nothing
since instead of having direct battery temp property under power supply I have
separate iio sensor, which may not even be monitored. It is always nice to have
battery explosions.

>
> Best regards,
> Krzysztof
>