On Wed, 10 Sep 2014 14:14:24 +0200
Johan Hovold [off-list ref] wrote:

On Wed, Sep 03, 2014 at 10:45:34AM +0200, Boris BREZILLON wrote:

quoted

Signed-off-by: Boris BREZILLON <redacted>
---
 .../devicetree/bindings/rtc/atmel,at91sam9-rtc.txt   | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/rtc/atmel,at91sam9-rtc.txt

diff --git a/Documentation/devicetree/bindings/rtc/atmel,at91sam9-rtc.txt b/Documentation/devicetree/bindings/rtc/atmel,at91sam9-rtc.txt
new file mode 100644
index 0000000..9ca455f
--- /dev/null
+++ b/Documentation/devicetree/bindings/rtc/atmel,at91sam9-rtc.txt

@@ -0,0 +1,20 @@
+Atmel AT91SAM9260 Real Time Timer
+
+Required properties:
+- compatible: should be: "atmel,at91sam9260-rtt"
+- reg: should contain 2 memory regions
+  * the first one encodes the memory region of the RTT controller
+  * the second one encodes the GPBR (General Purpose Backup Resgisters)
+    memory region used to store the current time
+- interrupts: rtc alarm/event interrupt
+- clocks: should contain one clock pointing the the slow clk
+
+Example:
+
+rtc@fffffe00 {
+	compatible = "atmel,at91sam9260-rtt";
+	reg = <0xfffffd20 0x10
+	       0xfffffd50 0x4>;
+	interrupts = <1 4 7>;
+	clocks = <&clk32k>;
+};

This does not describe the hardware, but rather a specific software
configuration.

The RTT is first of all not an RTC (although it can be used as one in a
specific software configuration). And the second register resource above
is not an RTT register, but a general-purpose backup register could be
used for other purposes (which register to use is currently configurable
for legacy booting using CONFIG_RTC_DRV_AT91SAM9_GPBR).

We could use a syscon device (which exposes a regmap) for the GPBR
block.

rtc@ffffff20 {
	compatible = "atmel,at91sam9260-rtt";
	reg = <0xfffffd20 0x10>;
	interrupts = <1 4 7>;
	clocks = <&clk32k>;
	atmel,time-reg = <&gpbr 0x0>;
};

gpbr: syscon@fffffd50 {
	compatible = "atmel,at91sam9260-gpbr", "syscon";
	reg = <0xfffffd50 0x10>;
	
};

This was discussed in the thread where I posted an RFC for this last
year (which you linked to in your original submission thread), but no
conclusion was reached:

	http://www.spinics.net/lists/arm-kernel/msg236292.html

Johan

-- 
Boris Brezillon, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com