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 15:44:17 -0500
From:   "Limonciello, Mario" <mlimonci@....com>
To:     Sebastian Reichel <sebastian.reichel@...labora.com>,
        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


On 5/16/2023 3:41 PM, Sebastian Reichel wrote:
> 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.

Yup!

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

Yes, that's correct.  I don't see a problem with the other patch going 
through
another tree.

> -- 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
>>