lib: add linear range get selector within

Add linear range get selector within for choose closest selector
between minimum and maximum selector.

Signed-off-by: Gene Chen <gene_chen@richtek.com>
Reviewed-by: Matti Vaittinen <matti.vaittinen@fi.rohmeurope.com>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>

lib/linear_ranges: fix repeated words & one typo

Change "which which" to "for which" in 3 places.
Change "ranges" to possessive "range's" in 1 place.

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Mark Brown <broonie@kernel.org>
Cc: Matti Vaittinen <matti.vaittinen@fi.rohmeurope.com>
Reviewed-by: Matti Vaittinen <matti.vaittinen@fi.rohmeurope.com>
Link: https://lore.kernel.org/r/20201221040610.12809-1-rdunlap@infradead.org
Signed-off-by: Mark Brown <broonie@kernel.org>

lib: linear_ranges: Add missing MODULE_LICENSE()

When linear_ranges is compiled as module we get warning
about missing MODULE_LICENSE(). Fix it by adding
MODULE_LICENSE("GPL") as is suggested by SPDX and EXPORTs.

Signed-off-by: Matti Vaittinen <matti.vaittinen@fi.rohmeurope.com>
Reviewed-by: Sebastian Reichel <sebastian.reichel@collabora.com>
Link: https://lore.kernel.org/r/20200509151519.GA7100@localhost.localdomain
Signed-off-by: Mark Brown <broonie@kernel.org>

lib: add linear ranges helpers

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.

Current implementation does not support inversely proportional ranges
but it might be useful if we could support also inversely proportional
ranges?

Signed-off-by: Matti Vaittinen <matti.vaittinen@fi.rohmeurope.com>
Reviewed-by: Mark Brown <broonie@kernel.org>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/59259bc475e0c800eb4bb163f02528c7c01f7b3a.1588944082.git.matti.vaittinen@fi.rohmeurope.com
Signed-off-by: Mark Brown <broonie@kernel.org>