mux: adgs1408: new driver for Analog Devices ADGS1408/1409 mux

This patch adds basic support for Analog Device ADGS1408/09 SPI mux
controller.

The device is probed and set to a disabled state. It uses the new mux
controller framework.

Signed-off-by: Mircea Caprioru <mircea.caprioru@analog.com>
Signed-off-by: Peter Rosin <peda@axentia.se>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

mux: add SPDX identifiers to all mux source files

Remove all free-text license texts.

This is done on a quest to remove the 700+ different ways that files in
the kernel describe the GPL license text.

No copyright headers or other non-license-description text was removed.

Reviewed-by: Philippe Ombredanne <pombredanne@nexb.com>
Acked-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Peter Rosin <peda@axentia.se>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

mux: zap mux- prefix from the source files

Preserve the module names with Makefile additions.

Signed-off-by: Peter Rosin <peda@axentia.se>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

mux: mmio-based syscon mux controller

This adds a driver for mmio-based syscon multiplexers controlled by
bitfields in a syscon register range.

Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Peter Rosin <peda@axentia.se>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

mux: adg792a: add mux controller driver for ADG792A/G

Analog Devices ADG792A/G is a triple 4:1 mux.

Reviewed-by: Jonathan Cameron <jic23@kernel.org>
Signed-off-by: Peter Rosin <peda@axentia.se>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

mux: gpio: add mux controller driver for gpio based multiplexers

The driver builds a single multiplexer controller using a number
of gpio pins. For N pins, there will be 2^N possible multiplexer
states. The GPIO pins can be connected (by the hardware) to several
multiplexers, which in that case will be operated in parallel.

Reviewed-by: Jonathan Cameron <jic23@kernel.org>
Signed-off-by: Peter Rosin <peda@axentia.se>
Reviewed-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

mux: minimal mux subsystem

Add a new minimalistic subsystem that handles multiplexer controllers.
When multiplexers are used in various places in the kernel, and the
same multiplexer controller can be used for several independent things,
there should be one place to implement support for said multiplexer
controller.

A single multiplexer controller can also be used to control several
parallel multiplexers, that are in turn used by different subsystems
in the kernel, leading to a need to coordinate multiplexer accesses.
The multiplexer subsystem handles this coordination.

Thanks go out to Lars-Peter Clausen, Jonathan Cameron, Rob Herring,
Wolfram Sang, Paul Gortmaker, Dan Carpenter, Colin Ian King, Greg
Kroah-Hartman and last but certainly not least to Philipp Zabel for
helpful comments, reviews, patches and general encouragement!

Reviewed-by: Jonathan Cameron <jic23@kernel.org>
Signed-off-by: Peter Rosin <peda@axentia.se>
Reviewed-by: Philipp Zabel <p.zabel@pengutronix.de>
Tested-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>