dt-bindings: ddr: Add bindings for LPDDR3 memories

Specifies the AC timing parameters of the LPDDR3 memory device.

Signed-off-by: Lukasz Luba <l.luba@partner.samsung.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>

Documentation/devicetree/bindings/ddr/lpddr3-timings.txt

@@ -0,0 +1,58 @@
+* AC timing parameters of LPDDR3 memories for a given speed-bin.
+
+The structures are based on LPDDR2 and extended where needed.
+
+Required properties:
+- compatible : Should be "jedec,lpddr3-timings"
+- min-freq : minimum DDR clock frequency for the speed-bin. Type is <u32>
+- reg : 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).
+- tRFC
+- tRRD
+- tRPab
+- tRPpb
+- tRCD
+- tRC
+- tRAS
+- tWTR
+- tWR
+- tRTP
+- tW2W-C2C
+- tR2R-C2C
+- tFAW
+- tXSR
+- tXP
+- tCKE
+- tCKESR
+- tMRD
+
+Example:
+
+timings_samsung_K3QF2F20DB_800mhz: lpddr3-timings@800000000 {
+	compatible	= "jedec,lpddr3-timings";
+	reg		= <800000000>; /* workaround: it shows max-freq */
+	min-freq	= <100000000>;
+	tRFC		= <65000>;
+	tRRD		= <6000>;
+	tRPab		= <12000>;
+	tRPpb		= <12000>;
+	tRCD		= <10000>;
+	tRC		= <33750>;
+	tRAS		= <23000>;
+	tWTR		= <3750>;
+	tWR		= <7500>;
+	tRTP		= <3750>;
+	tW2W-C2C	= <0>;
+	tR2R-C2C	= <0>;
+	tFAW		= <25000>;
+	tXSR		= <70000>;
+	tXP		= <3750>;
+	tCKE		= <3750>;
+	tCKESR		= <3750>;
+	tMRD		= <7000>;
+};