doc: renesas: add Renesas board docs
As a starting point, list all currently supported Renesas boards.
For the RZ/N1 board, add details about booting and flashing.
Signed-off-by: Ralph Siemsen <ralph.siemsen@linaro.org>
Reviewed-by: Marek Vasut <marek.vasut+renesas@mailbox.org>
diff --git a/doc/board/renesas/rzn1.rst b/doc/board/renesas/rzn1.rst
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+.. SPDX-License-Identifier: GPL-2.0+
+
+Renesas RZ/N1
+=============
+
+Building
+--------
+
+This document describes how to build and flash U-Boot for the RZ/N1.
+
+U-Boot
+^^^^^^
+
+Clone the U-Boot repository and build it as follows:
+
+.. code-block:: bash
+
+ git clone --depth 1 https://source.denx.de/u-boot/u-boot.git
+ cd u-boot
+ make rzn1_snarc_defconfig
+ make CROSS_COMPILE=arm-linux-gnu-
+
+This produces `u-boot` which is an ELF executable, suitable for use with `gdb`
+and JTAG debugging tools.
+
+It also produceds `u-boot.bin` which is a raw binary.
+
+Binman
+^^^^^^
+
+The BootROM in the RZ/N1 SoC expects to find the boot image in SPKG format.
+This format is documented in Chapter 7.4 of the RZ/N1 User Manual.
+
+The `binman` tool may be used to generate the SPKG format for booting.
+See tools/binman/binman.rst for details on this tool and its pre-requisites.
+
+.. code-block:: bash
+
+ binman -d arch/arm/dts/r9a06g032-rzn1-snarc.dtb -o <OUT>
+
+This will produce `u-boot.bin.spkg` in the specified <OUT> directory. It can
+then be flashed into QSPI, NAND, or loaded via USB-DFU mode.
+
+SPKG image
+^^^^^^^^^^
+
+Alternatively, the same SPKG image can be built by calling `mkimage` as follows:
+
+.. code-block:: bash
+
+ tools/mkimage -n board/schneider/rzn1-snarc/spkgimage.cfg \
+ -T spkgimage -a 0x20040000 -e 0x20040000 \
+ -d u-boot.bin u-boot.bin.spkg
+
+This produces `u-boot.bin.spkg` which can be flashed into QSPI, NAND, or loaded
+via USB-DFU mode.
+
+Take note of the load and execution address, which are encoded into the SPKG
+headers. For development convenience, mkimage computes the execution offset
+(part of the SPKG header) by subtracting the supplied load address from the
+supplied execution address.
+
+Also note there are other parameters, notably ECC configuration in the case of
+boot from NAND, specified in the `spkgimage.cfg` configuration file.
+
+Flashing
+--------
+
+The RZ/N1 is able to boot from QSPI, NAND, or via USB (DFU). In all cases the
+on-board BootROM expects for the binary to be wrapped with a "SPKG" header.
+
+It is possible to recover a bricked unit by using the USB (DFU) boot mode. This
+allows uploading U-Boot into the internal RAM. Thereafter U-Boot can be used to
+program the QSPI and/or NAND, making use of U-Boot dfu mode.
+
+Otherwise the only other option for recovery is via JTAG.