Add README.mpc8536ds

Add boot from NAND/eSDHC/eSPI description

Signed-off-by: Mingkai Hu <Mingkai.hu@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>

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+Overview:
+=========
+
+The MPC8536E integrates a PowerPC processor core with system logic
+required for imaging, networking, and communications applications.
+
+Boot from NAND:
+===============
+
+The MPC8536E is capable of booting from NAND flash which uses the image
+u-boot-nand.bin. This image contains two parts: a first stage image(also
+call 4K NAND loader and a second stage image. The former is appended to
+the latter to produce u-boot-nand.bin.
+
+The bootup process can be divided into two stages: the first stage will
+configure the L2SRAM, then copy the second stage image to L2SRAM and jump
+to it. The second stage image is to configure all the hardware and boot up
+to U-Boot command line.
+
+The 4K NAND loader's code comes from the corresponding nand_spl directory,
+along with the code twisted by CONFIG_NAND_SPL. The macro CONFIG_NAND_SPL
+is mainly used to shrink the code size to the 4K size limitation.
+
+The macro CONFIG_SYS_RAMBOOT is used to control the code to produce the
+second stage image. It's set in the board config file when boot from NAND
+is selected.
+
+Build and boot steps
+--------------------
+
+1. Building image
+       make MPC8536DS_NAND_config
+       make CROSS_COMPILE=powerpc-none-linux-gnuspe- all
+
+2. Change dip-switch
+       SW2[5-8] = 1011
+       SW9[1-3] = 101
+       Note: 1 stands for 'on', 0 stands for 'off'
+
+3. Flash image
+       tftp 1000000 u-boot-nand.bin
+       nand erase 0 a0000
+       nand write 1000000 0 a0000
+
+Boot from On-chip ROM:
+======================
+
+The MPC8536E is capable of booting from the on-chip ROM - boot from eSDHC
+and boot from eSPI. When power on, the porcessor excutes the ROM code to
+initialize the eSPI/eSDHC controller, and loads the mian U-Boot image from
+the memory device that interfaced to the controller, such as the SDCard or
+SPI EEPROM, to the target memory, e.g. SDRAM or L2SRAM, then boot from it.
+
+The memory device should contain a specific data structure with control word
+and config word at the fixed address. The config word direct the process how
+to config the memory device, and the control word direct the processor where
+to find the image on the memory device, or where copy the main image to. The
+user can use any method to store the data structure to the memory device, only
+if store it on the assigned address.
+
+Build and boot steps
+--------------------
+
+For boot from eSDHC:
+1. Build image
+       make MPC8536DS_SDCARD_config
+       make CROSS_COMPILE=powerpc-none-linux-gnuspe- all
+
+2. Change dip-switch
+       SW2[5-8] = 0111
+       SW3[1]   = 0
+       SW8[7]   = 0 - The on-board SD/MMC slot is active
+       SW8[7]   = 1 - The externel SD/MMC slot is active
+
+3. Put image to SDCard
+       Put the follwing info at the assigned address on the SDCard:
+
+          Offset   |   Data     | Description
+       --------------------------------------------------------
+       | 0x40-0x43 | 0x424F4F54 | BOOT signature              |
+       --------------------------------------------------------
+       | 0x48-0x4B | 0x00080000 | u-boot.bin's size           |
+       --------------------------------------------------------
+       | 0x50-0x53 | 0x???????? | u-boot.bin's Addr on SDCard |
+       --------------------------------------------------------
+       | 0x58-0x5B | 0xF8F80000 | Target Address              |
+       -------------------------------------------------------
+       | 0x60-0x63 | 0xF8FFF000 | Execution Starting Address  |
+       --------------------------------------------------------
+       | 0x68-0x6B | 0x6        | Number of Config Addr/Data  |
+       --------------------------------------------------------
+       | 0x80-0x83 | 0xFF720100 | Config Addr 1               |
+       | 0x84-0x87 | 0xF8F80000 | Config Data 1               |
+       --------------------------------------------------------
+       | 0x88-0x8b | 0xFF720e44 | Config Addr 2               |
+       | 0x8c-0x8f | 0x0000000C | Config Data 2               |
+       --------------------------------------------------------
+       | 0x90-0x93 | 0xFF720000 | Config Addr 3               |
+       | 0x94-0x97 | 0x80010000 | Config Data 3               |
+       --------------------------------------------------------
+       | 0x98-0x9b | 0xFF72e40e | Config Addr 4               |
+       | 0x9c-0x9f | 0x00000040 | Config Data 4               |
+       --------------------------------------------------------
+       | 0xa0-0xa3 | 0x40000001 | Config Addr 5               |
+       | 0xa4-0xa7 | 0x00000100 | Config Data 5               |
+       --------------------------------------------------------
+       | 0xa8-0xab | 0x80000001 | Config Addr 6               |
+       | 0xac-0xaf | 0x80000001 | Config Data 6               |
+       --------------------------------------------------------
+       |              ......                                  |
+       --------------------------------------------------------
+       | 0x???????? | u-boot.bin                              |
+       --------------------------------------------------------
+
+       then insert the SDCard to the active slot to boot up.
+
+For boot from eSPI:
+1. Build image
+       make MPC8536DS_SPIFLASH_config
+       make CROSS_COMPILE=powerpc-none-linux-gnuspe- all
+
+2. Change dip-switch
+       SW2[5-8] = 0110
+
+3. Put image to SPI flash
+       Put the info in the above table onto the SPI flash, then
+       boot up.