linux-kernel - Re: [PATCH 2/4] power_supply: Introduce generic psy charging driver

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Date:	Wed, 12 Mar 2014 15:37:17 +0100
From:	Linus Walleij <linus.walleij@...aro.org>
To:	Pavel Machek <pavel@....cz>
Cc:	Jenny TC <jenny.tc@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Dmitry Eremin-Solenikov <dbaryshkov@...il.com>,
	Anton Vorontsov <cbouatmailru@...il.com>,
	Anton Vorontsov <anton.vorontsov@...aro.org>,
	Kim Milo <Milo.Kim@...com>, Lee Jones <lee.jones@...aro.org>,
	Jingoo Han <jg1.han@...sung.com>,
	Chanwoo Choi <cw00.choi@...sung.com>,
	Sachin Kamat <sachin.kamat@...aro.org>,
	Lars-Peter Clausen <lars@...afoo.de>,
	Pali Rohár <pali.rohar@...il.com>,
	Rhyland Klein <rklein@...dia.com>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	David Woodhouse <dwmw2@...radead.org>,
	Tony Lindgren <tony@...mide.com>,
	Russell King <linux@....linux.org.uk>,
	Sebastian Reichel <sre@...g0.de>,
	Aaro Koskinen <aaro.koskinen@....fi>,
	Pallala Ramakrishna <ramakrishna.pallala@...el.com>,
	Ивайло Димитров <freemangordon@....bg>,
	Linux-OMAP <linux-omap@...r.kernel.org>
Subject: Re: [PATCH 2/4] power_supply: Introduce generic psy charging driver

On Fri, Mar 7, 2014 at 9:10 PM, Pavel Machek <pavel@....cz> wrote:
> On Fri 2014-03-07 11:04:59, Linus Walleij wrote:
>> On Fri, Feb 28, 2014 at 6:01 PM, Pavel Machek <pavel@....cz> wrote:
>> > On Thu 2014-02-27 21:08:01, Linus Walleij wrote:
>> >> On Thu, Feb 20, 2014 at 6:53 AM, Jenny TC <jenny.tc@...el.com> wrote:
>> >>
>> >> > +++ b/include/linux/power/power_supply_charger.h
>> >>
>> >> > +#define MAX_CUR_VOLT_SAMPLES 3
>> >> > +#define DEF_CUR_VOLT_SAMPLE_JIFF (30*HZ)
>> >>
>> >> Why are things defined in Jiffies like this insead of seconds, milliseconds
>> >> etc? This will vary with the current operating frequency of the system,
>> >> why should physical measurements do that?
>> >
>> > It is actually ok. The define is relative to jiffies, and that's what
>> > interface expects.
>>
>> So consider the option that the interface is wrong.
>>
>> Stating something like a sample period in system-specific jiffies
>> instead of period time T is just weird. What control systems
>> guy would understand this?
>
> 30*HZ means 30 seconds in the kernel... what is hard to understand
> about it?

Well I might be picky, but since it is a charging algorithm dealing with
ampères, volts, constant-current/constant-voltage, watchdogs and
timeouts, all stated in SI units, it would be nice if all such constants
were specified in simple units instead of kernel-specific terms.

One reason is that this kind of code actually needs review from
non-programmers, people like chemists and physicists.

I know it may be far fetched so no strong preference for sure.

Yours,
Linus Walleij
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