[U-Boot] [PATCH 2/2][v2] Add readme of how to boot from espi flash for p4080ds.

[Shaohui Xie]

Signed-off-by: Shaohui Xie <b21989 at freescale.com>
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+Overview:
+=========
+The P4080 integrates a pre-boot-loader(PBL) which performs configuration
+registers read and write to initialize external memory devices such as I2c,
+eLBC FCM(NAND flash), eSDHC, or SPI interface, loads RCW and/or pre-boot
+initialization commands from those devices before the local cores are permitted
+to boot.
+
+Boot from SPI:
+==============
+
+The P4080 is capable of booting from SPI. The bootup process can be divided into
+two stages: the first stage will load RCW and write configuration registers to
+initialize SPI interface, and configure one CPC as 1M SRAM, and loads U-boot image
+to CPC. The second stage will configure all the hardware and boot up to U-Boot
+command line.
+
+The PBL image contains three parts, the first is RCW, the second is PBI commands
+performs configuration registers write, the third is the 512KB u-boot image. The
+PBL image is produced by tool pbl_image_tool.html.
+
+Build and boot steps
+--------------------
+
+1. Producing RCW
+Copy RCW of u-boot dump and paste it to tab "Tools" of the tool and choose
+"RCW[0:511] U-Boot CCSR Dump" and then click button "Decode PBL", switch to tab
+"Boot" and change PBI_SRC to "0b0101 - SPI 24b Addressing", change BOOT_LOC to
+"0b10000 - Memory Complex 1"(if CPC2 is used as SRAM, this should be set as
+"0b10001 - Memory Complex 2").
+
+2. Producing ACS File
+	make P4080DS_PBL_BOOT_INDIRECT_config
+	make CROSS_COMPILE=powerpc-none-linux-gnuspe- all
+	xxd u-boot.bin > u-boot.xxd
+
+3. Producing PBI commands
+Switch to tab "PBI" and paste commands below into text field (please note these
+commands are for CPC1 used as SRAM only, change corresponding register setting
+if CPC2 need to be used as SRAM), then choose "ACS File (XXD Object Dump)",
+change Offset to "f80000", and click "Browse" to select the u-boot.xxd file
+produced in step 2, and click "Add PBI Data", after it finished, paste
+"09138000 00000000" and "091380c0 00000000" at the end.
+
+Below are Commands pasted before click "Add PBI Data".
+
+		PBI DATA      |	Description
+	-----------------------------------------
+	|  09010000 00200400  |	CPCFI &		|
+	|  09138000 00000000  |	CPCLFC for CPC1	|
+	|  091380c0 00000100  |			|
+	-----------------------------------------
+	|  09010100 00000000  |	Configure	|
+	|  09010104 fff0000b  |	CPC1 as		|
+	|  09010f00 08000000  |	1M SRAM		|
+	|  09010000 80000000  |			|
+	-----------------------------------------
+	|  09000d00 00000000  |	Configure	|
+	|  09000d04 fff00000  |	LAW for CPC1	|
+	|  09000d08 81000013  |			|
+	-----------------------------------------
+	|  09000010 00000000  |	Configure	|
+	|  09000014 ff000000  |	Alternate	|
+	|  09000018 81000000  |	for CPC1	|
+	-----------------------------------------
+	|  09110000 80000403  |	Initialize	|
+	|  09110020 2d170008  |	SPI interface	|
+	|  09110024 00100008  |			|
+	|  09110028 00100008  |			|
+	|  0911002c 00100008  |			|
+	-----------------------------------------
+	|  09138000 00000000  |	Flush command	|
+	|  091380c0 00000000  |			|
+	-----------------------------------------
+
+4. Producing PBL image
+	1. Switch to tab "Tools" and click "Encode PBL", after it finished copy
+the encoded content to file and save as x.xxd.
+	2. xxd -r x.xxd > pbl_u-boot.bin
+
+5. Put image to SPI flash
+	Put the pbl_u-boot.bin to SPI flash from offset 0.
+
+6. Change dip-switch
+	Change SW1[2] = off, then power on.
-- 
1.6.4