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 11:46:05 +0100
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Svyatoslav Ryhel <clamor95@...il.com>
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

On 08/03/2023 10:23, Svyatoslav Ryhel wrote:
> 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

Of course will tell you - via IIO.

> 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.

Hm, ok, I defer this to Sebastian. What's the policy - who should report
battery temperature if the battery/FG itself does not have any sensor?

Best regards,
Krzysztof