dt-bindings: mtd: add Marvell NAND controller documentation

Document the legacy and the new bindings for Marvell NAND controller.

The pxa3xx_nand.c driver does only support legacy bindings, which are
incomplete and inaccurate. A rework of this controller (called
marvell_nand.c) does support both.
Signed-off-by: Miquel Raynal <miquel.raynal@free-electrons.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>

Documentation/devicetree/bindings/mtd/marvell-nand.txt

+Marvell NAND Flash Controller (NFC)
+
+Required properties:
+- compatible: can be one of the following:
+    * "marvell,armada-8k-nand-controller"
+    * "marvell,armada370-nand-controller"
+    * "marvell,pxa3xx-nand-controller"
+    * "marvell,armada-8k-nand" (deprecated)
+    * "marvell,armada370-nand" (deprecated)
+    * "marvell,pxa3xx-nand" (deprecated)
+  Compatibles marked deprecated support only the old bindings described
+  at the bottom.
+- reg: NAND flash controller memory area.
+- #address-cells: shall be set to 1. Encode the NAND CS.
+- #size-cells: shall be set to 0.
+- interrupts: shall define the NAND controller interrupt.
+- clocks: shall reference the NAND controller clock.
+- marvell,system-controller: Set to retrieve the syscon node that handles
+  NAND controller related registers (only required with the
+  "marvell,armada-8k-nand[-controller]" compatibles).
+
+Optional properties:
+- label: see partition.txt. New platforms shall omit this property.
+- dmas: shall reference DMA channel associated to the NAND controller.
+  This property is only used with "marvell,pxa3xx-nand[-controller]"
+  compatible strings.
+- dma-names: shall be "rxtx".
+  This property is only used with "marvell,pxa3xx-nand[-controller]"
+  compatible strings.
+
+Optional children nodes:
+Children nodes represent the available NAND chips.
+
+Required properties:
+- reg: shall contain the native Chip Select ids (0-3).
+- nand-rb: see nand.txt (0-1).
+
+Optional properties:
+- marvell,nand-keep-config: orders the driver not to take the timings
+  from the core and leaving them completely untouched. Bootloader
+  timings will then be used.
+- label: MTD name.
+- nand-on-flash-bbt: see nand.txt.
+- nand-ecc-mode: see nand.txt. Will use hardware ECC if not specified.
+- nand-ecc-algo: see nand.txt. This property is essentially useful when
+  not using hardware ECC. Howerver, it may be added when using hardware
+  ECC for clarification but will be ignored by the driver because ECC
+  mode is chosen depending on the page size and the strength required by
+  the NAND chip. This value may be overwritten with nand-ecc-strength
+  property.
+- nand-ecc-strength: see nand.txt.
+- nand-ecc-step-size: see nand.txt. Marvell's NAND flash controller does
+  use fixed strength (1-bit for Hamming, 16-bit for BCH), so the actual
+  step size will shrink or grow in order to fit the required strength.
+  Step sizes are not completely random for all and follow certain
+  patterns described in AN-379, "Marvell SoC NFC ECC".
+
+See Documentation/devicetree/bindings/mtd/nand.txt for more details on
+generic bindings.
+
+
+Example:
+nand_controller: nand-controller@d0000 {
+	compatible = "marvell,armada370-nand-controller";
+	reg = <0xd0000 0x54>;
+	#address-cells = <1>;
+	#size-cells = <0>;
+	interrupts = <GIC_SPI 84 IRQ_TYPE_LEVEL_HIGH>;
+	clocks = <&coredivclk 0>;
+
+	nand@0 {
+		reg = <0>;
+		label = "main-storage";
+		nand-rb = <0>;
+		nand-ecc-mode = "hw";
+		marvell,nand-keep-config;
+		nand-on-flash-bbt;
+		nand-ecc-strength = <4>;
+		nand-ecc-step-size = <512>;
+
+		partitions {
+			compatible = "fixed-partitions";
+			#address-cells = <1>;
+			#size-cells = <1>;
+
+			partition@0 {
+				label = "Rootfs";
+				reg = <0x00000000 0x40000000>;
+			};
+		};
+	};
+};
+
+
+Note on legacy bindings: One can find, in not-updated device trees,
+bindings slightly different than described above with other properties
+described below as well as the partitions node at the root of a so
+called "nand" node (without clear controller/chip separation).
+
+Legacy properties:
+- marvell,nand-enable-arbiter: To enable the arbiter, all boards blindly
+  used it, this bit was set by the bootloader for many boards and even if
+  it is marked reserved in several datasheets, it might be needed to set
+  it (otherwise it is harmless) so whether or not this property is set,
+  the bit is selected by the driver.
+- num-cs: Number of chip-select lines to use, all boards blindly set 1
+  to this and for a reason, other values would have failed. The value of
+  this property is ignored.
+
+Example:
+
+	nand0: nand@43100000 {
+		compatible = "marvell,pxa3xx-nand";
+		reg = <0x43100000 90>;
+		interrupts = <45>;
+		dmas = <&pdma 97 0>;
+		dma-names = "rxtx";
+		#address-cells = <1>;
+		marvell,nand-keep-config;
+		marvell,nand-enable-arbiter;
+		num-cs = <1>;
+		/* Partitions (optional) */
+       };