linux-kernel - Re: Charge counter on droid 4

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Message-ID: <20180618093459.GA21391@amd>
Date:   Mon, 18 Jun 2018 11:34:59 +0200
From:   Pavel Machek <pavel@....cz>
To:     Tony Lindgren <tony@...mide.com>
Cc:     kernel list <linux-kernel@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-omap@...r.kernel.org, sre@...nel.org, nekit1000@...il.com,
        mpartap@....net, merlijn@...zup.org
Subject: Re: Charge counter on droid 4

On Mon 2018-06-18 01:28:58, Tony Lindgren wrote:
> * Pavel Machek <pavel@....cz> [180618 07:43]:
> > 
> > So... there are mA, mAh values. Those come from hardware, and I
> > believe we should keep them.
> > 
> > But there are also mW, mWh values, which are synthetic. Userland can
> > compute them from mV, mA values... and it is confusing that kernel
> > provides them. (My tendency was to start computing these synthetic
> > values in userland, to compare them with "real hardware" values from
> > kernel. But then I looked at kernel implementation, and realized they
> > are synthetic, tooo...)
> 
> Hmm mWh value is based on the hardware sampled shunt
> values and number of samples gathered between the
> two readings. I'd rather call the calculated values
> based on userland reading mV and mA values "synthetic" :)

As far as I know, shunt resistors provide you with current (mA) not
power (mW) measurement... and cpcap-battery computes power_now as
voltage * current. I'd rather have kernel tell me "hardware can't
measure power" and do "voltage*current" computation in userspace.

So I'm proposing to apply patch below.

Best regards,
								Pavel


+++ b/drivers/power/supply/cpcap-battery.c
@@ -490,24 +490,6 @@ static int cpcap_battery_get_property(struct power_supply *psy,
 	case POWER_SUPPLY_PROP_CHARGE_COUNTER:
 		val->intval = latest->counter_uah;
 		break;
-	case POWER_SUPPLY_PROP_POWER_NOW:
-		tmp = (latest->voltage / 10000) * latest->current_ua;
-		val->intval = div64_s64(tmp, 100);
-		break;
-	case POWER_SUPPLY_PROP_POWER_AVG:
-		if (cached) {
-			tmp = cpcap_battery_cc_get_avg_current(ddata);
-			tmp *= (latest->voltage / 10000);
-			val->intval = div64_s64(tmp, 100);
-			break;
-		}
-		sample = latest->cc.sample - previous->cc.sample;
-		accumulator = latest->cc.accumulator - previous->cc.accumulator;
-		tmp = cpcap_battery_cc_to_ua(ddata, sample, accumulator,
-					     latest->cc.offset);
-		tmp *= ((latest->voltage + previous->voltage) / 20000);
-		val->intval = div64_s64(tmp, 100);
-		break;
 	case POWER_SUPPLY_PROP_CAPACITY_LEVEL:
 		if (cpcap_battery_full(ddata))
 			val->intval = POWER_SUPPLY_CAPACITY_LEVEL_FULL;

-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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