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 10:08:36 +0100
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Svyatoslav Ryhel <clamor95@...il.com>,
        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>
Cc:     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 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.


Best regards,
Krzysztof