linux-kernel - Re: Charge counter on droid 4

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Mon, 18 Jun 2018 04:48:32 -0700
From:   Tony Lindgren <tony@...mide.com>
To:     Pavel Machek <pavel@....cz>
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

* 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?

Regards,

Tony