* Broadcom STB NAND Controller

The Broadcom Set-Top Box NAND controller supports low-level access to raw NAND
flash chips. It has a memory-mapped register interface for both control
registers and for its data input/output buffer. On some SoCs, this controller is
paired with a custom DMA engine (inventively named "Flash DMA") which supports
basic PROGRAM and READ functions, among other features.

This controller was originally designed for STB SoCs (BCM7xxx) but is now
available on a variety of Broadcom SoCs, including some BCM3xxx, BCM63xx, and
iProc/Cygnus. Its history includes several similar (but not fully register
compatible) versions.

Required properties:
- compatible       : May contain an SoC-specific compatibility string (see below)
                     to account for any SoC-specific hardware bits that may be
                     added on top of the base core controller.
                     In addition, must contain compatibility information about
                     the core NAND controller, of the following form:
                     "brcm,brcmnand" and an appropriate version compatibility
                     string, like "brcm,brcmnand-v7.0"
                     Possible values:
                         brcm,brcmnand-v4.0
                         brcm,brcmnand-v5.0
                         brcm,brcmnand-v6.0
                         brcm,brcmnand-v6.1
                         brcm,brcmnand-v6.2
                         brcm,brcmnand-v7.0
                         brcm,brcmnand-v7.1
                         brcm,brcmnand-v7.2
                         brcm,brcmnand-v7.3
                         brcm,brcmnand
- reg              : the register start and length for NAND register region.
                     (optional) Flash DMA register range (if present)
                     (optional) NAND flash cache range (if at non-standard offset)
- reg-names        : a list of the names corresponding to the previous register
                     ranges. Should contain "nand" and (optionally)
                     "flash-dma" and/or "nand-cache".
- interrupts       : The NAND CTLRDY interrupt and (if Flash DMA is available)
                     FLASH_DMA_DONE
- interrupt-names  : May be "nand_ctlrdy" or "flash_dma_done", if broken out as
                     individual interrupts.
                     May be "nand", if the SoC has the individual NAND
                     interrupts multiplexed behind another custom piece of
                     hardware
- #address-cells   : <1> - subnodes give the chip-select number
- #size-cells      : <0>

Optional properties:
- clock                     : reference to the clock for the NAND controller
- clock-names               : "nand" (required for the above clock)
- brcm,nand-has-wp          : Some versions of this IP include a write-protect
                              (WP) control bit. It is always available on >=
                              v7.0. Use this property to describe the rare
                              earlier versions of this core that include WP

 -- Additional SoC-specific NAND controller properties --

The NAND controller is integrated differently on the variety of SoCs on which it
is found. Part of this integration involves providing status and enable bits
with which to control the 8 exposed NAND interrupts, as well as hardware for
configuring the endianness of the data bus. On some SoCs, these features are
handled via standard, modular components (e.g., their interrupts look like a
normal IRQ chip), but on others, they are controlled in unique and interesting
ways, sometimes with registers that lump multiple NAND-related functions
together. The former case can be described simply by the standard interrupts
properties in the main controller node. But for the latter exceptional cases,
we define additional 'compatible' properties and associated register resources within the NAND controller node above.

 - compatible: Can be one of several SoC-specific strings. Each SoC may have
   different requirements for its additional properties, as described below each
   bullet point below.

   * "brcm,nand-bcm63138"
     - reg: (required) the 'NAND_INT_BASE' register range, with separate status
       and enable registers
     - reg-names: (required) "nand-int-base"

   * "brcm,nand-bcm6368"
     - compatible: should contain "brcm,nand-bcm<soc>", "brcm,nand-bcm6368"
     - reg: (required) the 'NAND_INTR_BASE' register range, with combined status
       and enable registers, and boot address registers
     - reg-names: (required) "nand-int-base"

   * "brcm,nand-iproc"
     - reg: (required) the "IDM" register range, for interrupt enable and APB
       bus access endianness configuration, and the "EXT" register range,
       for interrupt status/ack.
     - reg-names: (required) a list of the names corresponding to the previous
       register ranges. Should contain "iproc-idm" and "iproc-ext".


* NAND chip-select

Each controller (compatible: "brcm,brcmnand") may contain one or more subnodes
to represent enabled chip-selects which (may) contain NAND flash chips. Their
properties are as follows.

Required properties:
- compatible                : should contain "brcm,nandcs"
- reg                       : a single integer representing the chip-select
                              number (e.g., 0, 1, 2, etc.)
- #address-cells            : see partition.txt
- #size-cells               : see partition.txt

Optional properties:
- nand-ecc-strength         : see nand-controller.yaml
- nand-ecc-step-size        : must be 512 or 1024. See nand-controller.yaml
- nand-on-flash-bbt         : boolean, to enable the on-flash BBT for this
                              chip-select. See nand-controller.yaml
- brcm,nand-oob-sector-size : integer, to denote the spare area sector size
                              expected for the ECC layout in use. This size, in
                              addition to the strength and step-size,
                              determines how the hardware BCH engine will lay
                              out the parity bytes it stores on the flash.
                              This property can be automatically determined by
                              the flash geometry (particularly the NAND page
                              and OOB size) in many cases, but when booting
                              from NAND, the boot controller has only a limited
                              number of available options for its default ECC
                              layout.

Each nandcs device node may optionally contain sub-nodes describing the flash
partition mapping. See partition.txt for more detail.


Example:

nand@f0442800 {
	compatible = "brcm,brcmnand-v7.0", "brcm,brcmnand";
	reg = <0xF0442800 0x600>,
	      <0xF0443000 0x100>;
	reg-names = "nand", "flash-dma";
	interrupt-parent = <&hif_intr2_intc>;
	interrupts = <24>, <4>;

	#address-cells = <1>;
	#size-cells = <0>;

	nandcs@1 {
		compatible = "brcm,nandcs";
		reg = <1>; // Chip select 1
		nand-on-flash-bbt;
		nand-ecc-strength = <12>;
		nand-ecc-step-size = <512>;

		// Partitions
		#address-cells = <1>;  // <2>, for 64-bit offset
		#size-cells = <1>;     // <2>, for 64-bit length
		flash0.rootfs@0 {
			reg = <0 0x10000000>;
		};
		flash0@0 {
			reg = <0 0>; // MTDPART_SIZ_FULL
		};
		flash0.kernel@10000000 {
			reg = <0x10000000 0x400000>;
		};
	};
};

nand@10000200 {
	compatible = "brcm,nand-bcm63168", "brcm,nand-bcm6368",
		"brcm,brcmnand-v4.0", "brcm,brcmnand";
	reg = <0x10000200 0x180>,
	      <0x10000600 0x200>,
	      <0x100000b0 0x10>;
	reg-names = "nand", "nand-cache", "nand-int-base";
	interrupt-parent = <&periph_intc>;
	interrupts = <50>;
	clocks = <&periph_clk 20>;
	clock-names = "nand";

	#address-cells = <1>;
	#size-cells = <0>;

	nand0: nandcs@0 {
		compatible = "brcm,nandcs";
		reg = <0>;
		nand-on-flash-bbt;
		nand-ecc-strength = <1>;
		nand-ecc-step-size = <512>;
	};
};