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1c1608e0c7
Use board revision detection mechanism to choose correct DTB. Adjust documentation and build setup accordingly. Signed-off-by: Svyatoslav Ryhel <clamor95@gmail.com>
132 lines
4.3 KiB
ReStructuredText
132 lines
4.3 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0+
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U-Boot for the ASUS/Google Nexus 7 (2012)
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=========================================
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``DISCLAMER!`` Moving your ASUS/Google Nexus 7 (2012) to use U-Boot assumes
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replacement of the vendor ASUS bootloader. Vendor android firmwares will no
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longer be able to run on the device. This replacement IS reversible.
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Quick Start
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-----------
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- Build U-Boot
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- Process U-Boot
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- Flashing U-Boot into the eMMC
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- Boot
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- Self Upgrading
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Build U-Boot
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------------
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U-Boot features ability to detect grouper board revision on which it is
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loaded. Currently are supported both TI and MAXIM based WiFi-only models
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along with cellular one.
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.. code-block:: bash
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$ export CROSS_COMPILE=arm-linux-gnueabi-
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$ make grouper_defconfig # For all grouper versions and tilapia
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$ make
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After the build succeeds, you will obtain the final ``u-boot-dtb-tegra.bin``
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image, ready for further processing.
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Process U-Boot
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--------------
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``DISCLAMER!`` All questions related to the re-crypt work should be asked
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in re-crypt repo issues. NOT HERE!
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re-crypt is a tool that processes the ``u-boot-dtb-tegra.bin`` binary into form
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usable by device. This process is required only on the first installation or
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to recover the device in case of a failed update. You need to know your
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tablet's individual SBK to continue.
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Permanent installation can be performed either by using the nv3p protocol or by
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pre-loading just built U-Boot into RAM.
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Processing for the NV3P protocol
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********************************
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.. code-block:: bash
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$ git clone https://gitlab.com/grate-driver/re-crypt.git
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$ cd re-crypt # place your u-boot-dtb-tegra.bin here
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$ ./re-crypt.py --dev grouper --sbk <your sbk>
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where SBK has next form ``0xXXXXXXXX`` ``0xXXXXXXXX`` ``0xXXXXXXXX`` ``0xXXXXXXXX``
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The script will produce a ``repart-block.bin`` ready to flash.
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Processing for pre-loaded U-Boot
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********************************
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The procedure is the same, but the ``--split`` argument is used with the
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``re-crypt.py``. The script will produce ``bct.img`` and ``ebt.img`` ready
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to flash.
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Flashing U-Boot into the eMMC
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-----------------------------
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``DISCLAMER!`` All questions related to NvFlash should be asked in the proper
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place. NOT HERE! Flashing U-Boot will erase all eMMC, so make a backup before!
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Permanent installation can be performed either by using the nv3p protocol or by
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pre-loading just built U-Boot into RAM.
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Flashing with the NV3P protocol
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*******************************
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Nv3p is a custom Nvidia protocol used to recover bricked devices. Devices can
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enter it either by using ``wheelie`` with the correct ``blob.bin`` file or by
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pre-loading vendor bootloader with the Fusée Gelée.
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With nv3p, ``repart-block.bin`` is used. It contains BCT and a bootloader in
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encrypted state in form, which can just be written RAW at the start of eMMC.
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.. code-block:: bash
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$ wheelie --blob blob.bin
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$ nvflash --resume --rawdevicewrite 0 1024 repart-block.bin
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When flashing is done, reboot the device.
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Flashing with a pre-loaded U-Boot
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*********************************
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U-Boot pre-loaded into RAM acts the same as when it was booted "cold". Currently
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U-Boot supports bootmenu entry fastboot, which allows to write a processed copy
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of U-Boot permanently into eMMC.
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While pre-loading U-Boot, hold the ``volume down`` button which will trigger
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the bootmenu. There, select ``fastboot`` using the volume and power buttons.
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After, on host PC, do:
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.. code-block:: bash
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$ fastboot flash 0.1 bct.img
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$ fastboot flash 0.2 ebt.img
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$ fastboot reboot
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Device will reboot.
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Boot
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----
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To boot Linux, U-Boot will look for an ``extlinux.conf`` on eMMC. Additionally,
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if the Volume Down button is pressed while booting, the device will enter
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bootmenu. Bootmenu contains entries to mount eMMC as mass storage, fastboot,
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reboot, reboot RCM, poweroff, enter U-Boot console and update bootloader (check
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the next chapter).
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Flashing ``repart-block.bin`` eliminates vendor restrictions on eMMC and allows
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the user to use/partition it in any way the user desires.
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Self Upgrading
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--------------
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Place your ``u-boot-dtb-tegra.bin`` on the first partition of the eMMC (using
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ability of u-boot to mount it). Enter bootmenu, choose update bootloader option
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with Power button and U-Boot should update itself. Once the process is
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completed, U-Boot will ask to press any button to reboot.
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