linux-kernel - Re: [PATCH] mfd: axp20x: Add supplied-from property to axp288_fuel

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Message-ID: <YPVYc/mFKX14s1Yr@google.com>
Date:   Mon, 19 Jul 2021 11:48:19 +0100
From:   Lee Jones <lee.jones@...aro.org>
To:     Hans de Goede <hdegoede@...hat.com>
Cc:     Chen-Yu Tsai <wens@...e.org>, C++ / GCC <cpp@....lt>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mfd: axp20x: Add supplied-from property to
 axp288_fuel_gauge cell

On Sat, 17 Jul 2021, Hans de Goede wrote:

> The power-supply framework has the notion of one power-supply device
> being supplied by another. A typical example of this is a charger
> charging a battery.
> 
> A tablet getting plugged in to charge (or plugged out) only results in
> events seen by the axp288_charger device / MFD cell. Which means that
> a change udev-event only gets send for the charger power-supply class
> device, not for the battery (the axp288_fuel_gauge device).
> 
> The axp288_fuel_gauge does have an external_power_change'd callback
> which will generate a change udev-event when called. But before this
> commit this never got called because the power-supply core only calls
> this when a power-supply class device's supplier changes and the
> supplier link from axp288_charger to axp288_fuel_gauge was missing.
> 
> Add a "supplied-from" property to axp288_fuel_gauge cell, pointing
> to the "axp288_charger" power-supply class device, so that the
> axp288_fuel_gauge's external_power_change'd callback gets called on
> axp288_charger state changes.
> 
> Signed-off-by: Hans de Goede <hdegoede@...hat.com>
> ---
>  drivers/mfd/axp20x.c | 13 +++++++++++++
>  1 file changed, 13 insertions(+)
> 
> diff --git a/drivers/mfd/axp20x.c b/drivers/mfd/axp20x.c
> index d0ac019850d1..8161a5dc68e8 100644
> --- a/drivers/mfd/axp20x.c
> +++ b/drivers/mfd/axp20x.c
> @@ -700,6 +700,18 @@ static const struct resource axp288_charger_resources[] = {
>  	DEFINE_RES_IRQ(AXP288_IRQ_CBTO),
>  };
>  
> +static const char * const axp288_fuel_gauge_suppliers[] = { "axp288_charger" };
> +
> +static const struct property_entry axp288_fuel_gauge_properties[] = {
> +	PROPERTY_ENTRY_STRING_ARRAY("supplied-from", axp288_fuel_gauge_suppliers),
> +	{ }
> +};
> +
> +static const struct software_node axp288_fuel_gauge_sw_node = {
> +	.name = "axp288_fuel_gauge",
> +	.properties = axp288_fuel_gauge_properties,
> +};
> +
>  static const struct mfd_cell axp288_cells[] = {
>  	{
>  		.name		= "axp288_adc",
> @@ -717,6 +729,7 @@ static const struct mfd_cell axp288_cells[] = {
>  		.name		= "axp288_fuel_gauge",
>  		.num_resources	= ARRAY_SIZE(axp288_fuel_gauge_resources),
>  		.resources	= axp288_fuel_gauge_resources,
> +		.swnode		= &axp288_fuel_gauge_sw_node,
>  	}, {
>  		.name		= "axp221-pek",
>  		.num_resources	= ARRAY_SIZE(axp288_power_button_resources),

That's a lot of code to pass a string.

Is this really the most efficient method?

-- 
Lee Jones [李琼斯]
Senior Technical Lead - Developer Services
Linaro.org │ Open source software for Arm SoCs
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