drm/i915: Move abs_diff() to math.h

abs_diff() belongs to math.h. Move it there. This will allow others to
use it.

[andriy.shevchenko@linux.intel.com: add abs_diff() documentation]
Link: https://lkml.kernel.org/r/20230804050934.83223-1-andriy.shevchenko@linux.intel.com
[akpm@linux-foundation.org: fix comment, per Randy]
Link: https://lkml.kernel.org/r/20230803131918.53727-1-andriy.shevchenko@linux.intel.com
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Jiri Slaby <jirislaby@kernel.org> # tty/serial
Acked-by: Jani Nikula <jani.nikula@intel.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Andi Shyti <andi.shyti@linux.intel.com>
Reviewed-by: Philipp Zabel <p.zabel@pengutronix.de> # gpu/ipu-v3
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: David Airlie <airlied@gmail.com>
Cc: Helge Deller <deller@gmx.de>
Cc: Imre Deak <imre.deak@intel.com>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
Cc: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

include/linux/math.h: fix mult_frac() multiple argument evaluation bug

mult_frac() evaluates _all_ arguments multiple times in the body.

Clarify comment while I'm at it.

Link: https://lkml.kernel.org/r/f9f9fdbb-ec8e-4f5e-a998-2a58627a1a43@p183
Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

math.h: Introduce data types for fractional numbers

Introduce a macro to produce data types like

struct TYPE_fract {
__TYPE numerator;
__TYPE denominator;
};

to be used in the code wherever it's needed.

In the following changes convert some users to it.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20220126135353.24007-1-andriy.shevchenko@linux.intel.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

kernel.h: split out mathematical helpers

kernel.h is being used as a dump for all kinds of stuff for a long time.
Here is the attempt to start cleaning it up by splitting out
mathematical helpers.

At the same time convert users in header and lib folder to use new
header. Though for time being include new header back to kernel.h to
avoid twisted indirected includes for existing users.

[sfr@canb.auug.org.au: fix powerpc build]
Link: https://lkml.kernel.org/r/20201029150809.13059608@canb.auug.org.au

Link: https://lkml.kernel.org/r/20201028173212.41768-1-andriy.shevchenko@linux.intel.com
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Trond Myklebust <trond.myklebust@hammerspace.com>
Cc: Jeff Layton <jlayton@kernel.org>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>