board: asus: grouper: add Google Nexus 7 (2012) support

Nexus 7 is a mini tablet computer co-developed by Google and Asus
that runs the Android operating system. The Nexus 7 features a 7"
display, an Nvidia Tegra 3 quad-core chip, 1 GB of RAM and 8/16 GB
of internal storage.

This patch brings support for all 3 known ASUS/Google devices:
- Nexus 7 (2012) E1565
- Nexus 7 (2012) PM269
- Nexus 7 (2012) 3G - tilapia

Tested-by: Andreas Westman Dorcsak <[email protected]> # ASUS Grouper E1565
Tested-by: Svyatoslav Ryhel <[email protected]> # ASUS Grouper E1565
Signed-off-by: Svyatoslav Ryhel <[email protected]>
Signed-off-by: Thierry Reding <[email protected]>

2 files changed, 95 insertions, 0 deletions

diff --git a/doc/board/asus/grouper_common.rst b/doc/board/asus/grouper_common.rst
new file mode 100644
index 00000000000..2e4450b40e0
--- /dev/null
+++ b/doc/board/asus/grouper_common.rst
@@ -0,0 +1,94 @@
+.. SPDX-License-Identifier: GPL-2.0+
+
+U-Boot for the ASUS/Google Nexus 7 (2012)
+=========================================
+
+``DISCLAMER!`` Moving your ASUS/Google Nexus 7 (2012) to use
+U-Boot assumes replacement of the vendor ASUS 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 ``grouper_E1565.config``,
+``grouper_PM269.config`` and ``tilapia.config``.
+
+.. code-block:: bash
+
+    $ export CROSS_COMPILE=arm-linux-gnueabi-
+    $ make grouper_common_defconfig grouper_E1565.config # For maxim based grouper
+    $ 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.
+You need to know your tablet's individual SBK to continue.
+
+.. 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 grouper -k deadbeefdeadc0dedeadd00dfee1dead
+
+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`` configuration
+on eMMC. Additionally if Volume Down button is pressed while booting
+device will enter bootmenu. Bootmenu contains entries to mount 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.
diff --git a/doc/board/asus/index.rst b/doc/board/asus/index.rst
index c59571c8b3a..87e535fe34f 100644
--- a/doc/board/asus/index.rst
+++ b/doc/board/asus/index.rst
@@ -6,4 +6,5 @@ ASUS
 .. toctree::
    :maxdepth: 2
 
+   grouper_common
    transformer_t30