Android Fastboot
  ~~~~~~~~~~~~~~~~
  
  Overview
  ========
  The protocol that is used over USB is described in
  README.android-fastboot-protocol in same directory.
  
  The current implementation is a minimal support of the erase command,the
  "oem format" command and flash command;it only supports eMMC devices.
  
  Client installation
  ===================
  The counterpart to this gadget is the fastboot client which can
  be found in Android's platform/system/core repository in the fastboot
  folder. It runs on Windows, Linux and even OSX. Linux user are lucky since
  they only need libusb.
  Windows users need to bring some time until they have Android SDK (currently
  http://dl.google.com/android/installer_r12-windows.exe) installed. You
  need to install ADB package which contains the required glue libraries for
  accessing USB. Also you need "Google USB driver package" and "SDK platform
  tools". Once installed the usb driver is placed in your SDK folder under
  extras\google\usb_driver. The android_winusb.inf needs a line like
  
     %SingleBootLoaderInterface% = USB_Install, USB\VID_0451&PID_D022
  
  either in the [Google.NTx86] section for 32bit Windows or [Google.NTamd64]
  for 64bit Windows. VID and PID should match whatever the fastboot is
  advertising.
  
  Board specific
  ==============
  The fastboot gadget relies on the USB download gadget, so the following
  options must be configured:
  
  CONFIG_USB_GADGET_DOWNLOAD
  CONFIG_USB_GADGET_VENDOR_NUM
  CONFIG_USB_GADGET_PRODUCT_NUM
  CONFIG_USB_GADGET_MANUFACTURER
  
  NOTE: The CONFIG_USB_GADGET_VENDOR_NUM must be one of the numbers supported by
  the fastboot client. The list of vendor IDs supported can be found in the
  fastboot client source code (fastboot.c) mentioned above.
  
  The fastboot function is enabled by defining CONFIG_USB_FUNCTION_FASTBOOT,
  CONFIG_CMD_FASTBOOT and CONFIG_ANDROID_BOOT_IMAGE.
  
  The fastboot protocol requires a large memory buffer for downloads. This
  buffer should be as large as possible for a platform. The location of the
  buffer and size are set with CONFIG_FASTBOOT_BUF_ADDR and
  CONFIG_FASTBOOT_BUF_SIZE.
  
  Fastboot partition aliases can also be defined for devices where GPT
  limitations prevent user-friendly partition names such as "boot", "system"
  and "cache".  Or, where the actual partition name doesn't match a standard
  partition name used commonly with fastboot.  Current implentation checks
  aliases when accessing partitions by name (flash_write and erase functions).
  To define a partition alias add an environment variable similar to:
  fastboot_partition_alias_<alias partition name>=<actual partition name>
  Example: fastboot_partition_alias_boot=LNX
  
  Partition Names
  ===============
  The Fastboot implementation in U-boot allows to write images into disk
  partitions (currently on eMMC). Target partitions are referred on the host
  computer by their names.
  
  For GPT/EFI the respective partition name is used.
  
  For MBR the partitions are referred by generic names according to the
  following schema:
  
    <device type> <device index letter> <partition index>
  
  Example: hda3, sdb1, usbda1
  
  The device type is as follows:
  
    * IDE, ATAPI and SATA disks: hd
    * SCSI disks: sd
    * USB media: usbd
    * MMC and SD cards: mmcsd
    * Disk on chip: docd
    * other: xx
  
  The device index starts from 'a' and refers to the interface (e.g. USB
  controller, SD/MMC controller) or disk index. The partition index starts
  from 1 and describes the partition number on the particular device.
  
  Writing Partition Table
  =======================
  Fastboot also allows to write the partition table to the media. This can be
  done by writing the respective partition table image to a special target
  "gpt" or "mbr". These names can be customized by defining the following
  configuration options:
  
  CONFIG_FASTBOOT_GPT_NAME
  CONFIG_FASTBOOT_MBR_NAME
  
  In Action
  =========
  Enter into fastboot by executing the fastboot command in u-boot and you
  should see:
  |GADGET DRIVER: usb_dnl_fastboot
  
  On the client side you can fetch the bootloader version for instance:
  |>fastboot getvar bootloader-version
  |bootloader-version: U-Boot 2014.04-00005-gd24cabc
  |finished. total time: 0.000s
  
  or initiate a reboot:
  |>fastboot reboot
  
  and once the client comes back, the board should reset.
  
  You can also specify a kernel image to boot. You have to either specify
  the an image in Android format _or_ pass a binary kernel and let the
  fastboot client wrap the Android suite around it. On OMAP for instance you
  take zImage kernel and pass it to the fastboot client:
  
  |>fastboot -b 0x80000000 -c "console=ttyO2 earlyprintk root=/dev/ram0
  |	mem=128M" boot zImage
  |creating boot image...
  |creating boot image - 1847296 bytes
  |downloading 'boot.img'...
  |OKAY [  2.766s]
  |booting...
  |OKAY [ -0.000s]
  |finished. total time: 2.766s
  
  and on the gadget side you should see:
  |Starting download of 1847296 bytes
  |........................................................
  |downloading of 1847296 bytes finished
  |Booting kernel..
  |## Booting Android Image at 0x81000000 ...
  |Kernel load addr 0x80008000 size 1801 KiB
  |Kernel command line: console=ttyO2 earlyprintk root=/dev/ram0 mem=128M
  |   Loading Kernel Image ... OK
  |OK
  |
  |Starting kernel ...