mfd: syscon: Add Atmel GPBR DT bindings documention

The GPBR block provides a set of battery-backed registers that can be used
to save data which need to be kept when the system is powered down and
VDD-core is maintained by an external battery.

A typical usage is the RTT block (when used as an RTC) which needs one of
those registers to save the current time.

Signed-off-by: Boris BREZILLON <boris.brezillon@free-electrons.com>
Acked-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Acked-by: Johan Hovold <johan@kernel.org>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

diff --git a/Documentation/devicetree/bindings/mfd/atmel,gpbr.txt b/Documentation/devicetree/bindings/mfd/atmel,gpbr.txt
new file mode 100644 (file)
index 0000000..a285695
--- /dev/null
+++ b/Documentation/devicetree/bindings/mfd/atmel,gpbr.txt
@@ -0,0 +1,15 @@
+* Device tree bindings for Atmel GPBR (General Purpose Backup Registers)
+
+The GPBR are a set of battery-backed registers.
+
+Required properties:
+- compatible:          "atmel,at91sam9260-gpbr", "syscon"
+- reg:                 contains offset/length value of the GPBR memory
+                       region.
+
+Example:
+
+gpbr: gpbr@fffffd50 {
+       compatible = "atmel,at91sam9260-gpbr", "syscon";
+       reg = <0xfffffd50 0x10>;
+};