Documentation: dt: device tree bindings for LPDDR2 memories

device tree bindings for LPDDR2 SDRAM memories compliant
to JESD209-2 standard.

The 'lpddr2' binding in-turn uses another binding 'lpddr2-timings'
for specifying the AC timing parameters of the memory device at
different speed-bins.

Reviewed-by: Benoit Cousson <b-cousson@ti.com>
Reviewed-by: Grant Likely <grant.likely@secretlab.ca>
Tested-by: Lokesh Vutla <lokeshvutla@ti.com>
Signed-off-by: Aneesh V <aneesh@ti.com>
[santosh.shilimkar@ti.com: Rebased against 3.6-rc]
Signed-off-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Signed-off-by: Benoit Cousson <b-cousson@ti.com>

Documentation/devicetree/bindings/lpddr2/lpddr2-timings.txt

@@ -0,0 +1,52 @@
+* AC timing parameters of LPDDR2(JESD209-2) memories for a given speed-bin
+
+Required properties:
+- compatible : Should be "jedec,lpddr2-timings"
+- min-freq : minimum DDR clock frequency for the speed-bin. Type is <u32>
+- max-freq : maximum DDR clock frequency for the speed-bin. Type is <u32>
+
+Optional properties:
+
+The following properties represent AC timing parameters from the memory
+data-sheet of the device for a given speed-bin. All these properties are
+of type <u32> and the default unit is ps (pico seconds). Parameters with
+a different unit have a suffix indicating the unit such as 'tRAS-max-ns'
+- tRCD
+- tWR
+- tRAS-min
+- tRRD
+- tWTR
+- tXP
+- tRTP
+- tDQSCK-max
+- tFAW
+- tZQCS
+- tZQinit
+- tRPab
+- tZQCL
+- tCKESR
+- tRAS-max-ns
+- tDQSCK-max-derated
+
+Example:
+
+timings_elpida_ECB240ABACN_400mhz: lpddr2-timings@0 {
+	compatible	= "jedec,lpddr2-timings";
+	min-freq	= <10000000>;
+	max-freq	= <400000000>;
+	tRPab		= <21000>;
+	tRCD		= <18000>;
+	tWR		= <15000>;
+	tRAS-min	= <42000>;
+	tRRD		= <10000>;
+	tWTR		= <7500>;
+	tXP		= <7500>;
+	tRTP		= <7500>;
+	tCKESR		= <15000>;
+	tDQSCK-max	= <5500>;
+	tFAW		= <50000>;
+	tZQCS		= <90000>;
+	tZQCL		= <360000>;
+	tZQinit		= <1000000>;
+	tRAS-max-ns	= <70000>;
+};