board: wexler: qc750: add WEXLER Tab 7t support

WEXLER Tab 7t is a mini tablet computer developed by WEXLER that
runs the Android operating system. The device features a 7.0-inch
(180 mm) HD display, an Nvidia Tegra 3 quad-core chip, 1 GB of RAM,
8, 16 or 32 GB of storage that can be supplemented with a microSDXC
card giving up to 64 GB of additional storage and a full size USB
port.

Tested-by: Maksim Kurnosenko <asusx2@mail.ru>
Signed-off-by: Svyatoslav Ryhel <clamor95@gmail.com>

3 files changed, 135 insertions, 0 deletions

diff --git a/doc/board/index.rst b/doc/board/index.rst
index 2340eeb..9d31390 100644
--- a/doc/board/index.rst
+++ b/doc/board/index.rst
@@ -58,5 +58,6 @@ Board-specific doc
    ti/index
    toradex/index
    variscite/index
+   wexler/index
    xen/index
    xilinx/index
diff --git a/doc/board/wexler/index.rst b/doc/board/wexler/index.rst
new file mode 100644
index 0000000..308aad7
--- /dev/null
+++ b/doc/board/wexler/index.rst
@@ -0,0 +1,9 @@
+.. SPDX-License-Identifier: GPL-2.0+
+
+WEXLER
+======
+
+.. toctree::
+   :maxdepth: 2
+
+   qc750
diff --git a/doc/board/wexler/qc750.rst b/doc/board/wexler/qc750.rst
new file mode 100644
index 0000000..adef3c8
--- /dev/null
+++ b/doc/board/wexler/qc750.rst
@@ -0,0 +1,125 @@
+.. SPDX-License-Identifier: GPL-2.0+
+
+U-Boot for the WEXLER QC750 tablet
+==================================
+
+``DISCLAMER!`` Moving your WEXLER QC750 to use U-Boot assumes replacement
+of the vendor bootloader. Vendor Android firmwares will no longer be able
+to run on the device. This replacement IS reversible.
+
+Quick Start
+-----------
+
+- Build U-Boot
+- Process U-Boot
+- Flashing U-Boot into the eMMC
+- Boot
+- Self Upgrading
+
+Build U-Boot
+------------
+
+.. code-block:: bash
+
+    $ export CROSS_COMPILE=arm-linux-gnueabi-
+    $ make qc750_defconfig
+    $ make
+
+After the build succeeds, you will obtain the final ``u-boot-dtb-tegra.bin``
+image, ready for further processing.
+
+Process U-Boot
+--------------
+
+``DISCLAMER!`` All questions related to the re-crypt work should be asked
+in re-crypt repo issues. NOT HERE!
+
+re-crypt is a tool that processes the ``u-boot-dtb-tegra.bin`` binary into form
+usable by device. This process is required only on the first installation or
+to recover the device in case of a failed update.
+
+Permanent installation can be performed either by using the tegrarcm or by
+pre-loading just built U-Boot into RAM.
+
+Processing for the NV3P protocol
+********************************
+
+.. code-block:: bash
+
+    $ git clone https://gitlab.com/grate-driver/re-crypt.git
+    $ cd re-crypt # place your u-boot-dtb-tegra.bin here
+    $ ./re-crypt.py --dev qc750
+
+The script will produce a ``repart-block.bin`` ready to flash.
+
+Processing for pre-loaded U-Boot
+********************************
+
+The procedure is the same, but the ``--split`` argument is used with the
+``re-crypt.py``. The script will produce ``bct.img`` and ``ebt.img`` ready
+to flash.
+
+Flashing U-Boot into the eMMC
+-----------------------------
+
+``DISCLAMER!`` All questions related to tegrarcm should be asked in the proper
+place. NOT HERE! Flashing U-Boot will erase all eMMC, so make a backup before!
+
+Permanent installation can be performed either by using the nv3p protocol or by
+pre-loading just built U-Boot into RAM.
+
+Flashing with the NV3P protocol
+*******************************
+
+Nv3p is a custom Nvidia protocol used to recover bricked devices. Devices can
+enter it either by using ``wheelie`` with the correct ``blob.bin`` file or by
+pre-loading vendor bootloader with the Fusée Gelée.
+
+With nv3p, ``repart-block.bin`` is used. It contains BCT and a bootloader in
+encrypted state in form, which can just be written RAW at the start of eMMC.
+
+.. code-block:: bash
+
+    $ wheelie --bct qc750.bct --bl bootloader.bin
+    $ nvflash --resume --rawdevicewrite 0 1024 repart-block.bin
+
+When flashing is done, reboot the device.
+
+Flashing with a pre-loaded U-Boot
+*********************************
+
+U-Boot pre-loaded into RAM acts the same as when it was booted "cold". Currently
+U-Boot supports bootmenu entry fastboot, which allows to write a processed copy
+of U-Boot permanently into eMMC.
+
+While pre-loading U-Boot, hold the ``volume down`` button which will trigger
+the bootmenu. There, select ``fastboot`` using the volume and power buttons.
+After, on host PC, do:
+
+.. code-block:: bash
+
+    $ fastboot flash 0.1 bct.img
+    $ fastboot flash 0.2 ebt.img
+    $ fastboot reboot
+
+Device will reboot.
+
+Boot
+----
+
+To boot Linux, U-Boot will look for an ``extlinux.conf`` on MicroSD and then on
+eMMC. Additionally, if the Volume Down button is pressed while booting, the
+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 the next chapter).
+
+Flashing ``repart-block.bin`` eliminates vendor restrictions 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 MicroSD card
+and insert it into the tablet. Enter bootmenu, choose update the bootloader
+option with the Power button and U-Boot should update itself. Once the process
+is completed, U-Boot will ask to press any button to reboot.