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>

gpio-fsm: Fix a build warning

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

gpio-fsm: Rename 'num-soft-gpios' to avoid warning

As of 5.10, the Device Tree parser warns about properties that look
like references to "suppliers" of various services. "num-soft-gpios"
resembles a declaration of a GPIO called "num-soft", causing the value
to be interpreted as a phandle, the owner of which is checked for a
"#gpio-cells" property.

To avoid this warning, rename the gpio-fsm property to "num-swgpios".

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

gpio-fsm: Show state info in /sys/class/gpio-fsm

Add gpio-fsm sysfs entries under /sys/class/gpio-fsm. For each state
machine show the current state, which state (if any) will be entered
after a delay, and the current value of that delay.

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

gpio-fsm: Fix shutdown timeout handling

The driver is intended to jump directly to a shutdown state in the
event of a timeout during shutdown, but the sense of the test was
inverted.

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

gpio-fsm: Clamp the delay time to zero

The sysfs delay_ms value is calculated live, and it is possible for
the time left to appear to be negative briefly if the timer handling
hasn't completed. Ensure the displayed value never goes below zero,
for the sake of appearances.

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

gpio-fsm: Sort functions into a more logical order

Move some functions into a more logical ordering. This change causes
no functional change and is essentially cosmetic.

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

gpio_fsm: Rework the atomic-vs-non-atomic split

Partition the code to separate atomic and non-atomic methods so that
none of them have to handle both cases. The result avoids using deferred
work unless necessary, and should be easier to understand.

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

drivers/gpio/Kconfig

@@ -1428,6 +1428,15 @@ config GPIO_ELKHARTLAKE
 	  To compile this driver as a module, choose M here: the module will
 	  be called gpio-elkhartlake.
 
+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

@@ -70,6 +70,7 @@ obj-$(CONFIG_GPIO_EN7523)		+= gpio-en7523.o
 obj-$(CONFIG_GPIO_EP93XX)		+= gpio-ep93xx.o
 obj-$(CONFIG_GPIO_EXAR)			+= gpio-exar.o
 obj-$(CONFIG_GPIO_F7188X)		+= gpio-f7188x.o
+obj-$(CONFIG_GPIO_FSM)			+= gpio-fsm.o
 obj-$(CONFIG_GPIO_FTGPIO010)		+= gpio-ftgpio010.o
 obj-$(CONFIG_GPIO_FXL6408)		+= gpio-fxl6408.o
 obj-$(CONFIG_GPIO_GE_FPGA)		+= gpio-ge.o