power: Add simple gpio-restart driver

This driver registers a restart handler to set a GPIO line high/low
to reset a board based on devicetree bindings.

Signed-off-by: David Riley <davidriley@chromium.org>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Sebastian Reichel <sre@kernel.org>

1 files changed, 54 insertions, 0 deletions

diff --git a/Documentation/devicetree/bindings/gpio/gpio-restart.txt b/Documentation/devicetree/bindings/gpio/gpio-restart.txt
new file mode 100644
index 00000000000..af3701bc15c
--- /dev/null
+++ b/Documentation/devicetree/bindings/gpio/gpio-restart.txt
@@ -0,0 +1,54 @@
+Drive a GPIO line that can be used to restart the system from a restart
+handler.
+
+This binding supports level and edge triggered reset.  At driver load
+time, the driver will request the given gpio line and install a restart
+handler. If the optional properties 'open-source' is not found, the GPIO line
+will be driven in the inactive state.  Otherwise its not driven until
+the restart is initiated.
+
+When the system is restarted, the restart handler will be invoked in
+priority order.  The gpio is configured as an output, and driven active,
+triggering a level triggered reset condition. This will also cause an
+inactive->active edge condition, triggering positive edge triggered
+reset. After a delay specified by active-delay, the GPIO is set to
+inactive, thus causing an active->inactive edge, triggering negative edge
+triggered reset. After a delay specified by inactive-delay, the GPIO
+is driven active again.  After a delay specified by wait-delay, the
+restart handler completes allowing other restart handlers to be attempted.
+
+Required properties:
+- compatible : should be "gpio-restart".
+- gpios : The GPIO to set high/low, see "gpios property" in
+  Documentation/devicetree/bindings/gpio/gpio.txt. If the pin should be
+  low to reset the board set it to "Active Low", otherwise set
+  gpio to "Active High".
+
+Optional properties:
+- open-source : Treat the GPIO as being open source and defer driving
+  it to when the restart is initiated.  If this optional property is not
+  specified, the GPIO is initialized as an output in its inactive state.
+- priority : A priority ranging from 0 to 255 (default 128) according to
+  the following guidelines:
+	0:	Restart handler of last resort, with limited restart
+		capabilities
+	128:	Default restart handler; use if no other restart handler is
+		expected to be available, and/or if restart functionality is
+		sufficient to restart the entire system
+	255:	Highest priority restart handler, will preempt all other
+		restart handlers
+- active-delay: Delay (default 100) to wait after driving gpio active [ms]
+- inactive-delay: Delay (default 100) to wait after driving gpio inactive [ms]
+- wait-delay: Delay (default 3000) to wait after completing restart
+  sequence [ms]
+
+Examples:
+
+gpio-restart {
+	compatible = "gpio-restart";
+	gpios = <&gpio 4 0>;
+	priority = <128>;
+	active-delay = <100>;
+	inactive-delay = <100>;
+	wait-delay = <3000>;
+};