linux-kernel - Re: [PATCH 1/2] power: supply: Use the scope of power supplies to tell if power is system supplied

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Date:   Tue, 16 May 2023 22:41:14 +0200
From:   Sebastian Reichel <sebastian.reichel@...labora.com>
To:     Mario Limonciello <mario.limonciello@....com>
Cc:     heikki.krogerus@...ux.intel.com, rafael@...nel.org,
        ajayg@...dia.com, andriy.shevchenko@...ux.intel.com,
        linux-i2c@...r.kernel.org, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org,
        Evan.Quan@....com, Lijo.Lazar@....com, Sanket.Goswami@....com
Subject: Re: [PATCH 1/2] power: supply: Use the scope of power supplies to
 tell if power is system supplied

Hi,

On Tue, May 16, 2023 at 01:25:40PM -0500, Mario Limonciello wrote:
> The logic used for power_supply_is_system_supplied() counts all power
> supplies and:
> * If no power supplies found assumes AC
> * If non-battery power supplies found uses online to determine AC/DC.
>   - If any are onlined, assumes AC
>   - Othewise DC.
> 
> This logic makes sense for desktop systems that don't export an ACPI
> battery, but it fails once you include a dGPU that provides a UCSI
> power supply on a desktop system without any other power supplies.
> 
> The dGPU by default doesn't have anything plugged in so it's 'offline'.
> This makes power_supply_is_system_supplied() return 0 with a count of
> 1 meaning all drivers that use this get a wrong judgement.
> 
> To fix this case adjust the logic to also examine the scope of the
> power supply. If the power supply is deemed a device power supply,
> then don't count it.
> 
> Cc: Evan Quan <Evan.Quan@....com>
> Suggested-by: Lijo Lazar <Lijo.Lazar@....com>
> Signed-off-by: Mario Limonciello <mario.limonciello@....com>
> ---

Good find; the current logic should also break with a desktop PC
once a POWER_SUPPLY_SCOPE_DEVICE battery device is attached (e.g.
a HID device), because it increases the counter.

I suppose I can just apply this to my fixes branch since there is
no compile time dependency to the second patch?

-- Sebastian

>  drivers/power/supply/power_supply_core.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/power/supply/power_supply_core.c b/drivers/power/supply/power_supply_core.c
> index ab986dbace16..d57f420ba8c3 100644
> --- a/drivers/power/supply/power_supply_core.c
> +++ b/drivers/power/supply/power_supply_core.c
> @@ -348,6 +348,10 @@ static int __power_supply_is_system_supplied(struct device *dev, void *data)
>  	struct power_supply *psy = dev_get_drvdata(dev);
>  	unsigned int *count = data;
>  
> +	if (!psy->desc->get_property(psy, POWER_SUPPLY_PROP_SCOPE, &ret))
> +		if (ret.intval == POWER_SUPPLY_SCOPE_DEVICE)
> +			return 0;
> +
>  	(*count)++;
>  	if (psy->desc->type != POWER_SUPPLY_TYPE_BATTERY)
>  		if (!psy->desc->get_property(psy, POWER_SUPPLY_PROP_ONLINE,
> @@ -366,8 +370,8 @@ int power_supply_is_system_supplied(void)
>  				      __power_supply_is_system_supplied);
>  
>  	/*
> -	 * If no power class device was found at all, most probably we are
> -	 * running on a desktop system, so assume we are on mains power.
> +	 * If no system scope power class device was found at all, most probably we
> +	 * are running on a desktop system, so assume we are on mains power.
>  	 */
>  	if (count == 0)
>  		return 1;
> -- 
> 2.34.1
> 

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