gpio: Add gpio-fsm driver

The gpio-fsm driver implements simple state machines that allow GPIOs
to be controlled in response to inputs from other GPIOs - real and
soft/virtual - and time delays. It can:
+ create dummy GPIOs for drivers that demand them,
+ drive multiple GPIOs from a single input, with optional delays,
+ add a debounce circuit to an input,
+ drive pattern sequences onto LEDs
etc.

Signed-off-by: Phil Elwell <phil@raspberrypi.com>

drivers/gpio/Kconfig

@@ -1162,6 +1162,15 @@ config HTC_EGPIO
 	  several HTC phones.  It provides basic support for input
 	  pins, output pins, and irqs.
 
+config GPIO_FSM
+	tristate "GPIO FSM support"
+	help
+	  The GPIO FSM driver allows the creation of state machines for
+	  manipulating GPIOs (both real and virtual), with state transitions
+	  triggered by GPIO edges or delays.
+
+	  If unsure, say N.
+
 config GPIO_JANZ_TTL
 	tristate "Janz VMOD-TTL Digital IO Module"
 	depends on MFD_JANZ_CMODIO

drivers/gpio/Makefile

@@ -60,6 +60,7 @@ obj-$(CONFIG_GPIO_EP93XX)		+= gpio-ep93xx.o
 obj-$(CONFIG_GPIO_EXAR)			+= gpio-exar.o
 obj-$(CONFIG_GPIO_F7188X)		+= gpio-f7188x.o
 obj-$(CONFIG_GPIO_FTGPIO010)		+= gpio-ftgpio010.o
+obj-$(CONFIG_GPIO_FSM)			+= gpio-fsm.o
 obj-$(CONFIG_GPIO_GE_FPGA)		+= gpio-ge.o
 obj-$(CONFIG_GPIO_GPIO_MM)		+= gpio-gpio-mm.o
 obj-$(CONFIG_GPIO_GRGPIO)		+= gpio-grgpio.o

include/dt-bindings/gpio/gpio-fsm.h

@@ -0,0 +1,21 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+/*
+ * This header provides constants for binding rpi,gpio-fsm.
+ */
+
+#ifndef _DT_BINDINGS_GPIO_FSM_H
+#define _DT_BINDINGS_GPIO_FSM_H
+
+#define GF_IN       0
+#define GF_OUT      1
+#define GF_SOFT     2
+#define GF_DELAY    3
+#define GF_SHUTDOWN 4
+
+#define GF_IO(t, v) (((v) << 16) | ((t) & 0xffff))
+
+#define GF_IP(x)    GF_IO(GF_IN, (x))
+#define GF_OP(x)    GF_IO(GF_OUT, (x))
+#define GF_SW(x)    GF_IO(GF_SOFT, (x))
+
+#endif