linux-kernel - Re: [PATCH v4 3/9] drivers: base: add linear ranges helpers

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Message-ID: <910505f6a38298707fc27b135e49a7e2a941fb88.camel@fi.rohmeurope.com>
Date:   Wed, 18 Mar 2020 13:42:26 +0000
From:   "Vaittinen, Matti" <Matti.Vaittinen@...rohmeurope.com>
To:     "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
CC:     "rafael@...nel.org" <rafael@...nel.org>,
        "mazziesaccount@...il.com" <mazziesaccount@...il.com>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "broonie@...nel.org" <broonie@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "sre@...nel.org" <sre@...nel.org>,
        "Laine, Markus" <Markus.Laine@...rohmeurope.com>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
        "lgirdwood@...il.com" <lgirdwood@...il.com>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "Mutanen, Mikko" <Mikko.Mutanen@...rohmeurope.com>
Subject: Re: [PATCH v4 3/9] drivers: base: add linear ranges helpers

Hello Greg,

On Wed, 2020-03-18 at 14:08 +0100, Greg Kroah-Hartman wrote:
> On Tue, Feb 25, 2020 at 10:53:01AM +0200, Matti Vaittinen wrote:
> > Many devices have control registers which control some measurable
> > property. Often a register contains control field so that change in
> > this field causes linear change in the controlled property. It is
> > not
> > a rare case that user wants to give 'meaningful' control values and
> > driver needs to convert them to register field values. Even more
> > often user wants to 'see' the currently set value - again in
> > meaningful units - and driver needs to convert the values it reads
> > from register to these meaningful units. Examples of this include:
> > 
> > - regulators, voltage/current configurations
> > - power, voltage/current configurations
> > - clk(?) NCOs
> > 
> > and maybe others I can't think of right now.
> > 
> > Provide a linear_range helper which can do conversion from user
> > value
> > to register value 'selector'.
> > 
> > The idea here is stolen from regulator framework and patches
> > refactoring
> > the regulator helpers to use this are following.
> > 
> > Signed-off-by: Matti Vaittinen <matti.vaittinen@...rohmeurope.com>
> > ---
> > 
> > Changes since rfc-v3:
> >   - Kerneldoc fixes
> >   - Corrected commit message typo meaningfull => meaningful
> > 
> >  drivers/base/Kconfig         |   3 +
> >  drivers/base/Makefile        |   1 +
> >  drivers/base/linear_ranges.c | 246
> > +++++++++++++++++++++++++++++++++++
> 
> Why in drivers/base/ ?
> 
> Why not in lib/ ?

I was pondering which of these would be better. I decided to do with
drivers/base because - in it's current form - this is really a driver
related stuff. I see it somehow in same position as regmap code -
although this is just a tiny helper compared to regmap. But this also
has pretty driver specific audience :)

And... I must admit I like things which I know. And I have been doing
driver development and "know" a few of the driver related colleagues -
hence working with them is easier for me ;) Getting to know the
colleagues maintaining lib is a bit scary :] Yep, I'm Finnish if you
happen to wonder why getting to know people is scary xD

> 
> >  include/linux/linear_range.h |  48 +++++++
> >  4 files changed, 298 insertions(+)
> >  create mode 100644 drivers/base/linear_ranges.c
> >  create mode 100644 include/linux/linear_range.h
> > 
> > diff --git a/drivers/base/Kconfig b/drivers/base/Kconfig
> > index 5f0bc74d2409..636b6fa8e499 100644
> > --- a/drivers/base/Kconfig
> > +++ b/drivers/base/Kconfig
> > @@ -209,4 +209,7 @@ config GENERIC_ARCH_TOPOLOGY
> >  	  appropriate scaling, sysfs interface for reading capacity
> > values at
> >  	  runtime.
> >  
> > +config LINEAR_RANGES
> > +	tristate
> 
> No help text at all???

Yes. The linear ranges has no meaning to be enabled alone. It only
plays a role if it is used by some driver/subsystem. And
drivers/subsystems should do
select LINEAR_RANGES. So showing help in any config tool is not needed.
This should actually not be visible in menuconfig or others. I think I
have seen a few examples like this.

Ayways, I have no obejctions to adding some text if absolutely needed.
Any suggestions for a text politely saying - "please, pretend I am not
here" - are welcome :) (Although, I think this really does not need
help text).

> 
> > +EXPORT_SYMBOL(linear_range_values_in_range);
> 
> EXPORT_SYMBOL_GPL() for all of these?  I have to ask...

I personally have no objections towards EXPORT_SYMBOL_GPL. I guess
regulator helpers and the power supply modules which use this are GPL
modules. If no other (better) opinions, then I can change this in next
version. Thanks for pointing it out - I didn't even think about it.

> 
> > @@ -0,0 +1,48 @@
> > +/* SPDX-License-Identifier: GPL-2.0-or-later */
> 
> Are you sure about the "or later"?  Again, I have to ask.

No. If you want to educate me on this topic - or point a link to some
nice explanation why to not use "later" - pretty please. I would like
to learn :)

> 
> > +/* Copyright (C) 2020 ROHM Semiconductors */
> > +
> > +#ifndef LINEAR_RANGE_H
> > +#define LINEAR_RANGE_H
> > +
> > +#include <linux/types.h>
> 
> Why is this needed?

I think it was the bool type which was missing without this. At least
on my ARM gcc toolchain.

Best Regards
	Matti Vaittinen