U-Boot supports access of both ext2 and ext4 filesystems, either in read-only
  mode or in read-write mode.

  First, to enable support for both ext4 (and, automatically, ext2 as well),
  but without selecting the corresponding commands, use one of:

    #define CONFIG_FS_EXT4	(for read-only)
    #define CONFIG_EXT4_WRITE	(for read-write)

  Next, to select the ext2-related commands:

    * ext2ls
    * ext2load

  or ext4-related commands:

    * ext4size
    * ext4ls
    * ext4load

  use one or both of:

    #define CONFIG_CMD_EXT2
    #define CONFIG_CMD_EXT4
  
  Selecting either of the above automatically defines CONFIG_FS_EXT4 if it
  wasn't defined already.
  
  In addition, to get the write access command "ext4write", use:
  
    #define CONFIG_CMD_EXT4_WRITE
  
  which automatically defines CONFIG_EXT4_WRITE if it wasn't defined
  already.
  
  Also relevant are the generic filesystem commands, selected by:
  
    #define CONFIG_CMD_FS_GENERIC
  
  This does not automatically enable EXT4 support for you, you still need
  to do that yourself.
  
  Some sample commands to test ext4 support:

  1. Check that the commands can be seen in the output of U-Boot help:
  
  	UBOOT #help
  	...

  	ext4load- load binary file from a Ext4 file system
  	ext4ls  - list files in a directory (default /)

  	ext4size - determine a file's size

  	ext4write- create a file in ext4 formatted partition

  	...
  
  2. To list the files in an ext4-formatted partition, run:

  	ext4ls <interface> <dev[:part]> [directory]

  	For example:
  	UBOOT #ext4ls mmc 0:5 /usr/lib

  3. To read and load a file from an ext4-formatted partition to RAM, run:

  	ext4load <interface> <dev[:part]> [addr] [filename] [bytes]

  	For example:
  	UBOOT #ext4load mmc 2:2 0x30007fc0 uImage

  4. To write a file to an ext4-formatted partition.

  	a) First load a file to RAM at a particular address for example 0x30007fc0.

  	Now execute ext4write command:

  	ext4write <interface> <dev[:part]> [filename] [Address] [sizebytes]

  	For example:
  	UBOOT #ext4write mmc 2:2 /boot/uImage 0x30007fc0 6183120
  	(here 6183120 is the size of the file to be written)
  	Note: Absolute path is required for the file to be written

  
  References :
  	-- ext4 implementation in Linux Kernel
  	-- Uboot existing ext2 load and ls implementation
  	-- Journaling block device JBD2 implementation in linux Kernel