Documentation: dt: device tree bindings for LPDDR2 memories

* 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>;

};

* LPDDR2 SDRAM memories compliant to JEDEC JESD209-2

Required properties:

- compatible : Should be one of - "jedec,lpddr2-nvm", "jedec,lpddr2-s2",

  "jedec,lpddr2-s4"

  "ti,jedec-lpddr2-s2" should be listed if the memory part is LPDDR2-S2 type

  "ti,jedec-lpddr2-s4" should be listed if the memory part is LPDDR2-S4 type

  "ti,jedec-lpddr2-nvm" should be listed if the memory part is LPDDR2-NVM type

- density  : <u32> representing density in Mb (Mega bits)

- io-width : <u32> representing bus width. Possible values are 8, 16, and 32

Optional properties:

The following optional properties represent the minimum value of some AC

timing parameters of the DDR device in terms of number of clock cycles.

These values shall be obtained from the device data-sheet.

- tRRD-min-tck

- tWTR-min-tck

- tXP-min-tck

- tRTP-min-tck

- tCKE-min-tck

- tRPab-min-tck

- tRCD-min-tck

- tWR-min-tck

- tRASmin-min-tck

- tCKESR-min-tck

- tFAW-min-tck

Child nodes:

- The lpddr2 node may have one or more child nodes of type "lpddr2-timings".

  "lpddr2-timings" provides AC timing parameters of the device for

  a given speed-bin. The user may provide the timings for as many

  speed-bins as is required. Please see Documentation/devicetree/

  bindings/lpddr2/lpddr2-timings.txt for more information on "lpddr2-timings"

Example:

elpida_ECB240ABACN : lpddr2 {

	compatible	= "Elpida,ECB240ABACN","jedec,lpddr2-s4";

	density		= <2048>;

	io-width	= <32>;

	tRPab-min-tck	= <3>;

	tRCD-min-tck	= <3>;

	tWR-min-tck	= <3>;

	tRASmin-min-tck	= <3>;

	tRRD-min-tck	= <2>;

	tWTR-min-tck	= <2>;

	tXP-min-tck	= <2>;

	tRTP-min-tck	= <2>;

	tCKE-min-tck	= <3>;

	tCKESR-min-tck	= <3>;

	tFAW-min-tck	= <8>;

	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>;

	};

	timings_elpida_ECB240ABACN_200mhz: lpddr2-timings@1 {

		compatible	= "jedec,lpddr2-timings";

		min-freq	= <10000000>;

		max-freq	= <200000000>;

		tRPab		= <21000>;

		tRCD		= <18000>;

		tWR		= <15000>;

		tRAS-min	= <42000>;

		tRRD		= <10000>;

		tWTR		= <10000>;

		tXP		= <7500>;

		tRTP		= <7500>;

		tCKESR		= <15000>;

		tDQSCK-max	= <5500>;

		tFAW		= <50000>;

		tZQCS		= <90000>;

		tZQCL		= <360000>;

		tZQinit		= <1000000>;

		tRAS-max-ns	= <70000>;

	};

}