linux-kernel - Re: [PATCH 2/2] power: supply: max17042_battery: add technology property support

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Date:   Mon, 26 Sep 2016 18:32:52 +0200
From:   Krzysztof Kozlowski <krzk@...nel.org>
To:     Wolfgang Wiedmeyer <wolfgit@...dmeyer.de>
Cc:     Krzysztof Kozlowski <krzk@...nel.org>, sre@...nel.org,
        dbaryshkov@...il.com, dwmw2@...radead.org,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] power: supply: max17042_battery: add technology
 property support

On Mon, Sep 26, 2016 at 02:56:44PM +0200, Wolfgang Wiedmeyer wrote:
> 
> Krzysztof Kozlowski writes:
> 
> > On Sun, Sep 25, 2016 at 11:10:11PM +0200, Wolfgang Wiedmeyer wrote:
> >> This patch reports the battery technology as Li-ion.
> >> 
> >> Signed-off-by: Wolfgang Wiedmeyer <wolfgit@...dmeyer.de>
> >> ---
> >>  drivers/power/max17042_battery.c | 4 ++++
> >>  1 file changed, 4 insertions(+)
> >> 
> >> diff --git a/drivers/power/max17042_battery.c b/drivers/power/max17042_battery.c
> >> index 20cb1fd..43cb5df 100644
> >> --- a/drivers/power/max17042_battery.c
> >> +++ b/drivers/power/max17042_battery.c
> >> @@ -92,6 +92,7 @@ static enum power_supply_property max17042_battery_props[] = {
> >>  	POWER_SUPPLY_PROP_TEMP_MIN,
> >>  	POWER_SUPPLY_PROP_TEMP_MAX,
> >>  	POWER_SUPPLY_PROP_HEALTH,
> >> +	POWER_SUPPLY_PROP_TECHNOLOGY,
> >>  	POWER_SUPPLY_PROP_CURRENT_NOW,
> >>  	POWER_SUPPLY_PROP_CURRENT_AVG,
> >>  };
> >> @@ -296,6 +297,9 @@ static int max17042_get_property(struct power_supply *psy,
> >>  		if (ret < 0)
> >>  			return ret;
> >>  		break;
> >> +	case POWER_SUPPLY_PROP_TECHNOLOGY:
> >> +		val->intval = POWER_SUPPLY_TECHNOLOGY_LION;
> >
> > How can you be sure it is always Li-Ion? For wearables and mobiles, rather yes, but
> > the driver is also used in other devices. Technically, specs are saying
> > it might be used also with Li-Poly applications.
> 
> I suppose that there is no way to detect this. Would it be ok if I add
> an optional Device Tree property that allows to specify if it's Li-Ion
> or Li-Poly? If the property is not supplied, then "unknown" is returned.

I am not sure in such case what will be the benefit of exposing this to
user-space... but it won't harm neither and sounds like a valid usage of
DT properties. Fine with me.

Best regards,
Krzysztof