board: nvidia: tegratab: add Nvidia Tegra Note 7 support

The Tegra Note 7 is a mini tablet computer and the second Tegra 4
based mobile device designed by Nvidia that runs the Android operating
system. The Tegra Note has a 7" IPS display with 1280 x 800 (217 ppi)
resolution. The 1 GB of RAM and 16 GB of internal memory can be
supplemented with a microSDXC card giving up to 64 GB of additional
storage.

Signed-off-by: Svyatoslav Ryhel <clamor95@gmail.com>

2 files changed, 83 insertions, 0 deletions

diff --git a/doc/board/nvidia/index.rst b/doc/board/nvidia/index.rst
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+.. SPDX-License-Identifier: GPL-2.0+
+
+NVIDIA
+======
+
+.. toctree::
+   :maxdepth: 2
+
+   tegratab
diff --git a/doc/board/nvidia/tegratab.rst b/doc/board/nvidia/tegratab.rst
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+.. SPDX-License-Identifier: GPL-2.0+
+
+U-Boot for the Nvidia Tegra Note 7
+==================================
+
+Quick Start
+-----------
+
+- Build U-Boot
+- Boot U-Boot by loading it into RAM (coldboot)
+- Chainloading U-Boot from the vendor bootloader
+- Boot
+
+Build U-Boot
+------------
+
+U-Boot can be built in two forms: U-Boot with SPL, which is used for booting
+by loading directly into RAM and U-Boot without SPL, which can be flashed
+and chainloaded from the vendor bootloader.
+
+To build U-Boot with SPL proseed:
+
+.. code-block:: bash
+
+    $ export CROSS_COMPILE=arm-none-eabi-
+    $ make tegratab_defconfig
+    $ make
+
+After the build succeeds, you will obtain the final ``u-boot-dtb-tegra.bin``
+file, ready for cold booting by loading into RAM.
+
+To build U-Boot without SPL adjust tegratab_defconfig:
+
+.. code-block::
+
+  CONFIG_TEXT_BASE=0x80A00000
+  CONFIG_SKIP_LOWLEVEL_INIT=y
+  # CONFIG_OF_BOARD_SETUP is not set
+  CONFIG_TEGRA_SUPPORT_NON_SECURE=y
+
+After the build succeeds, you will obtain the final ``u-boot-dtb.bin`` file,
+ready for booting with fastboot boot or which can be further processed into
+a flashable boot.img.
+
+Boot U-Boot by loading it into RAM (coldboot)
+---------------------------------------------
+
+Done fairly simply by using fusee-tools (using run_bootloader.sh) and placing
+``u-boot-dtb-tegra.bin`` generated on the previous step into fusee-tools dir.
+This method requires constant access to the host PC or payloader and can fully
+eliminate influence of the vendor bootloader onto the boot process.
+
+.. code-block:: bash
+
+    $ ./run_bootloader.sh -s T114 -t ./bct/tegratab.bct
+
+Chainloading U-Boot from the vendor bootloader
+----------------------------------------------
+
+``u-boot-dtb.bin`` has to be further packed into Android boot image form,
+where ``u-boot-dtb.bin`` acts as kernel, while dtb and ramdisk parts should
+not be included. Then the generated boot image can be flashed into the /boot
+partition of the tablet using vendor bootloader's fastboot and will act as
+the bootloader of the last stage.
+
+Boot
+----
+In both cases after U-Boot obtains control it performs search of extlinux.conf
+first on the dock USB device is available, then on MicroSD card if available
+and lastly on eMMC. If none of the devices above are present, then the device
+is turned off.
+
+If during boot of U-Boot Volume Down button is pressed, the device will enter
+U-Boot bootmenu.