linux-kernel - Re: [PATCH v2 2/2] power: charger-manager: Avoid recursive thermal get

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Message-id: <1413190681.3829.7.camel@AMDC1943>
Date:	Mon, 13 Oct 2014 10:58:01 +0200
From:	Krzysztof Kozlowski <k.kozlowski@...sung.com>
To:	myungjoo.ham@...sung.com
Cc:	Sebastian Reichel <sre@...nel.org>,
	Dmitry Eremin-Solenikov <dbaryshkov@...il.com>,
	David Woodhouse <dwmw2@...radead.org>,
	Anton Vorontsov <anton@...msg.org>,
	이종화 <jonghwa3.lee@...sung.com>,
	최찬우 <cw00.choi@...sung.com>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	박경민 <kyungmin.park@...sung.com>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>
Subject: Re: [PATCH v2 2/2] power: charger-manager: Avoid recursive thermal
 get_temp call

On pon, 2014-10-13 at 06:01 +0000, MyungJoo Ham wrote:
> >   
> >  Add a 'no_thermal' property to the power supply class. If true then
> > thermal zone won't be created for this power supply in
> > power_supply_register().
> > 
> > Power supply drivers may want to set it if they support
> > POWER_SUPPLY_PROP_TEMP and they are forwarding this get property call to
> > other thermal zone.
> > 
> > If they won't set it lockdep may report false positive deadlock for
> > thermal zone's mutex because of nested calls to thermal_zone_get_temp().
> > First is the call to thermal_zone_get_temp() of the driver's thermal
> > zone. Thermal core gets POWER_SUPPLY_PROP_TEMP property from this
> > driver. The driver then calls other thermal zone thermal_zone_get_temp()
> > and returns result.
> > 
> > Example of such driver is charger manager.
> > 
> > Signed-off-by: Krzysztof Kozlowski <k.kozlowski@...sung.com>
> 
> Do we really need to add another variable in the psy struct?
> In the previous thread, I thought that wasn't needed, though.

I considered the idea mentioned by  Jonghwa Lee:

static int psy_register_thermal(struct power_supply *psy)
{
...
+       if (psy->tzd)
+               return 0; 

but there would be problem in determining the ownership of the thermal
zone - who should unregister that thermal zone? Charger manager's power
supply or fuel gauge's power supply?

We could NULL-ify it manually from charger's remove function before
calling power_supply_unregister... but it is really accessing a private
field of power_supply structure. 

I think this should be done in API-level.

Best regards,
Krzysztof

> 
> 
> Cheers,
> MyungJoo
> 
> > 
> > ---
> > 
> > Changes since v1:
> > 1. New patch (new idea).
> > ---
> >  drivers/power/power_supply_core.c | 3 +++
> >  include/linux/power_supply.h      | 6 ++++++
> >  2 files changed, 9 insertions(+)
> > 
> > diff --git a/drivers/power/power_supply_core.c b/drivers/power/power_supply_core.c
> > index 6cb7fe5c022d..694e8cddd5c1 100644
> > --- a/drivers/power/power_supply_core.c
> > +++ b/drivers/power/power_supply_core.c
> > @@ -417,6 +417,9 @@ static int psy_register_thermal(struct power_supply *psy)
> >  {
> >  	int i;
> >  
> > +	if (psy->no_thermal)
> > +		return 0;
> > +
> >  	/* Register battery zone device psy reports temperature */
> >  	for (i = 0; i < psy->num_properties; i++) {
> >  		if (psy->properties[i] == POWER_SUPPLY_PROP_TEMP) {
> > diff --git a/include/linux/power_supply.h b/include/linux/power_supply.h
> > index 3ed049673022..096dbced02ac 100644
> > --- a/include/linux/power_supply.h
> > +++ b/include/linux/power_supply.h
> > @@ -200,6 +200,12 @@ struct power_supply {
> >  	void (*external_power_changed)(struct power_supply *psy);
> >  	void (*set_charged)(struct power_supply *psy);
> >  
> > +	/*
> > +	 * Set if thermal zone should not be created for this power supply.
> > +	 * For example for virtual supplies forwarding calls to actual
> > +	 * sensors or other supplies.
> > +	 */
> > +	bool no_thermal;
> >  	/* For APM emulation, think legacy userspace. */
> >  	int use_for_apm;
> >  
> > -- 
> > 1.9.1
> > 

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