linux-kernel - Re: Charge counter on droid 4

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Message-ID: <20180704195655.GB13932@amd>
Date:   Wed, 4 Jul 2018 21:56:55 +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 04:48:32, Tony Lindgren wrote:
> * Pavel Machek <pavel@....cz> [180618 09:37]:
> > 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.
> 
> Yup you are correct the hardware samples mA and we still need
> to calculate mW based on the voltage.
> 
> But considering it works and seems to match the power supply
> provided average power consumption numbers pretty well and at
> least I'm using it.. What is your reasoning for removing such
> a usable interface?

Well, it is confusing for the userland, because it has no way of
knowing data is synthetic.

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

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