mx28evk: Add documentation on how to boot from SPI NOR

Explain the necessary steps in order to boot from SPI NOR.

Based on a earlier submission from Mårten Wikman.

Signed-off-by: Mårten Wikman <marten.wikman@novia.fi>
Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>

board/freescale/mx28evk/README

@@ -23,11 +23,19 @@ To boot MX28EVK from an SD card, set the boot mode DIP switches as:
    * VDD 5V: To the left (off)
    * Hold Button: Down (off)
 
+To boot MX28EVK from SPI NOR flash, set the boot mode DIP switches as:
+
+   * Boot Mode Select: 0 0 1 0 (Boot from SSP2)
+   * JTAG PSWITCH RESET: To the right (reset disabled)
+   * Battery Source: Down
+   * Wall 5V: Up
+   * VDD 5V: To the left (off)
+   * Hold Button: Down (off)
 
 Environment Storage
 -------------------
 
-There are two targets for mx28evk:
+There are three targets for mx28evk:
 
 "make mx28evk_config"		- store environment variables into MMC
 
@@ -35,12 +43,20 @@ or
 
 "make mx28evk_nand_config"	- store environment variables into NAND flash
 
+or
+
+"make mx28evk_spi_config"       - store enviroment variables into SPI NOR flash
+
 Choose the target accordingly.
 
 Note: The mx28evk board does not come with a NAND flash populated from the
 factory. It comes with an empty slot (U23), which allows the insertion of a
 48-pin TSOP flash device.
 
-Follow the instructions from doc/README.mxs to generate a bootable SD card.
+mx28evk does not come with SPI NOR flash populated from the factory either.
+It is possible to solder a SOIC memory on U49 or use a DIP8 on J89.
+To get SPI communication to work R320, R321,R322 and C178 need to be populated.
+Look in the schematics for the proper component values.
 
-Insert the SD card in slot 0, power up the board and U-boot will boot.
+Follow the instructions from doc/README.mxs to generate a bootable SD card or
+to generate a binary to be flashed into SPI NOR.

doc/README.mxs

@@ -23,6 +23,7 @@ Contents
 2) Compiling U-Boot for a MXS based board
 3) Installation of U-Boot for a MXS based board to SD card
 4) Installation of U-Boot into NAND flash on a MX28 based board
+5) Installation of U-boot into SPI NOR flash on a MX28 based board
 
 1) Prerequisites
 ----------------
@@ -262,3 +263,28 @@ There are two possibilities when preparing an image writable to NAND flash.
 	   In case the user needs to boot a firmware image bigger than 1Mb, the
 	   user has to adjust the "update_nand_firmware_maxsz" variable for the
 	   update scripts to work properly.
+
+5) Installation of U-Boot into SPI NOR flash on a MX28 based board
+------------------------------------------------------------------
+
+The u-boot.sb file can be directly written to SPI NOR from U-boot prompt.
+
+Load u-boot.sb into RAM, this can be done in several ways and one way is to use
+tftp:
+       => tftp u-boot.sb 0x42000000
+
+Probe the SPI NOR flash:
+       => sf probe
+
+(SPI NOR should be succesfully detected in this step)
+
+Erase the blocks where U-boot binary will be written to:
+       => sf erase 0x0 0x80000
+
+Write u-boot.sb to SPI NOR:
+       => sf write 0x42000000 0 0x80000
+
+Power off the board and set the boot mode DIP switches to boot from the SPI NOR
+according to MX28 manual section 12.2.1 (Table 12-2)
+
+Last step is to power up the board and U-boot should start from SPI NOR.