board: lg: x3: add Optimus 4X HD and Optimus Vu support

LG X3 is a development board based on Nvidia Tegra 3 SoC
on base of which Optimus 4X HD and Optimus Vu were created.
Both smartphones feature a 4.7" and 5" panels respectively,
an Nvidia Tegra 3 quad-core chip, 1 GB of RAM and 16/32 GB
of internal storage. Optimux 4X HD additionally has a micro
SD slot.

Tested-by: Andreas Westman Dorcsak <hedmoo@yahoo.com> # LG P880 T30
Tested-by: Svyatoslav Ryhel <clamor95@gmail.com> # LG P895 T30
Signed-off-by: Svyatoslav Ryhel <clamor95@gmail.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>

doc/board/index.rst

@@ -28,6 +28,7 @@ Board-specific doc
    highbank/index
    intel/index
    kontron/index
+   lg/index
    mediatek/index
    microchip/index
    nokia/index

doc/board/lg/index.rst

@@ -0,0 +1,9 @@
+.. SPDX-License-Identifier: GPL-2.0+
+
+LG
+==
+
+.. toctree::
+   :maxdepth: 2
+
+   x3_t30

doc/board/lg/x3_t30.rst

@@ -0,0 +1,93 @@
+.. SPDX-License-Identifier: GPL-2.0+
+
+U-Boot for the LG X3 T30 device family
+======================================
+
+``DISCLAMER!`` Moving your LG P880 or P895 to use U-Boot
+assumes replacement of the vendor LG bootloader. Vendor
+android firmwares will no longer be able to run on the
+device. This replacement IS reversible.
+
+Quick Start
+-----------
+
+- Build U-Boot
+- Pack U-Boot into repart-block
+- Flash repart-block into the eMMC
+- Boot
+- Self Upgrading
+
+Build U-Boot
+------------
+
+Device support is implemented by applying config fragment to a generic
+board defconfig. Valid fragments are ``p880.config`` and ``p895.config``.
+
+.. code-block:: bash
+
+    $ export CROSS_COMPILE=arm-linux-gnueabi-
+    $ make x3_t30_defconfig p895.config # For LG Optimus Vu
+    $ make
+
+After the build succeeds, you will obtain the final ``u-boot-dtb-tegra.bin``
+image, ready for flashing (but check the next section for additional
+adjustments).
+
+Pack U-Boot into repar-block
+----------------------------
+
+``DISCLAMER!`` All questions related to re-crypt work should be
+asked in re-crypt repo issues. NOT HERE!
+
+re-crypt is a small script which packs ``u-boot-dtb-tegra.bin`` in
+form usable by device. This process is required only on the first
+installation or to recover the device in case of a failed update.
+
+.. code-block:: bash
+
+    $ git clone https://github.com/clamor-s/re-crypt.git
+    $ cd re-crypt # place your u-boot-dtb-regra.bin here
+    $ ./re-crypt.sh -d p895
+
+Script will produce you a ``repart-block.bin`` ready to flash.
+
+Flash repart-block into the eMMC
+--------------------------------
+
+``DISCLAMER!`` All questions related to NvFlash should be asked
+in the proper place. NOT HERE! Flashing repart-block will erase
+all your eMMC, so make a backup before!
+
+``repart-block.bin`` contains BCT and bootloader in encrypted state
+in form which can just be written RAW at the start of eMMC.
+
+.. code-block:: bash
+
+    $ wheelie --blob blob.bin
+    $ nvflash --resume --rawdevicewrite 0 1024 repart-block.bin
+
+Boot
+----
+
+After flashing ``repart-block.bin`` the device should reboot and turn
+itself off. This is normal behavior if no boot configuration is
+found.
+
+To boot Linux, U-Boot will look for an ``extlinux.conf`` on MicroSD
+and then on eMMC. Additionally if Volume Down button is pressed
+while booting device will enter bootmenu. Bootmenu contains entries
+to mount MicroSD and eMMC as mass storage, fastboot, reboot, reboot
+RCM, poweroff, enter U-Boot console and update bootloader (check next
+chapter).
+
+Flashing ``repart-block.bin`` eliminates vendor restriction on eMMC
+and allows the user to use/partition it in any way the user desires.
+
+Self Upgrading
+--------------
+
+Place your ``u-boot-dtb-tegra.bin`` on the first partition of the
+eMMC (using ability of u-boot to mount it). Enter bootmenu, choose
+update bootloader option with Power button and U-Boot should update
+itself. Once the process is completed, U-Boot will ask to press any
+button to reboot.