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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Message-ID: <20230516215452.icwx6vb2763hybxs@mercury.elektranox.org>
Date:   Tue, 16 May 2023 23:54:52 +0200
From:   Sebastian Reichel <sebastian.reichel@...labora.com>
To:     "Limonciello, Mario" <mlimonci@....com>
Cc:     Mario Limonciello <mario.limonciello@....com>,
        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 03:44:17PM -0500, Limonciello, Mario wrote:
> 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.

Ok, I modified the commit message to also mention the HID issue and
applied it to power-supply's fixes branch.

Thanks,

-- Sebastian

> 
> > -- 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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