doc: canaan: Add K230 CanMV board

Add description of compiling u-boot for K230 CanMV.

Since the vendor's u-boot-spl verifies u-boot header [1], it is
necessary to use the Python script from vendor to add the header to the
u-boot image.

[1] https://github.com/kendryte/k230_sdk/blob/v1.8/src/little/uboot/board/canaan/common/k230_board_common.h#L52

Signed-off-by: Junhui Liu <junhui.liu@pigmoral.tech>
Reviewed-by: Leo Yu-Chi Liang <ycliang@andestech.com>

doc/board/canaan/index.rst

@@ -0,0 +1,8 @@
+.. SPDX-License-Identifier: GPL-2.0+
+
+Canaan
+======
+.. toctree::
+   :maxdepth: 1
+
+   k230_canmv

doc/board/canaan/k230_canmv.rst

@@ -0,0 +1,88 @@
+.. SPDX-License-Identifier: GPL-2.0+
+
+K230 CanMV
+==========
+
+K230 RISC-V SoC
+------------------
+The K230 chip is the latest generation SoC product in Canaan Technology's
+Kendryte series of AIOT chips.
+
+Mainline support
+----------------
+
+The support for following drivers are already enabled:
+
+1. ns16550 UART
+2. DWC2 OTG USB controller
+
+Building
+~~~~~~~~
+
+1. Get the RISC-V toolchain.
+2. Setup cross compilation environment variable:
+3. Get the `firmware_gen.py`_ from vendor.
+
+.. code-block:: console
+
+   export CROSS_COMPILE=riscv64-linux-gnu-
+   cd <U-Boot-dir>
+   make k230_canmv_defconfig
+   make
+   cp u-boot-gz.img u-boot-gz.img.tmp
+   pip install gmssl pycryptodome
+   python3 firmware_gen.py -i u-boot-gz.img.tmp -o u-boot-head.img -n
+
+This will generate u-boot-head.img.
+
+.. _firmware_gen.py: https://raw.githubusercontent.com/kendryte/k230_sdk/refs/tags/v1.8/src/little/uboot/tools/firmware_gen.py
+
+Booting
+~~~~~~~
+
+Currently, we rely on vendor u-boot-spl to initialize the
+ddr and load the u-boot image, then bootup from it.
+
+1. Prepare a SD card with the `vendor image`_ burned on it.
+
+2. Write the U-Boot image to the SD card at offset 2MB.
+
+.. code-block:: console
+
+   dd if=u-boot-head.img of=/dev/sd[x] bs=1M seek=2
+
+3. Insert the SD card into the board and power it on.
+
+.. _vendor image: https://kendryte-download.canaan-creative.com/developer/k230/CanMV-K230_debian_sdcard_sdk_1.3.img.gz
+
+Sample boot log from K230 CanMV board
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+.. code-block:: none
+
+   U-Boot 2025.01-00645-g2d81c4788455 (Jan 14 2025 - 23:15:07 +0800)
+
+   DRAM:  512 MiB
+   Core:  15 devices, 11 uclasses, devicetree: separate
+   Loading Environment from nowhere... OK
+   In:    serial@91400000
+   Out:   serial@91400000
+   Err:   serial@91400000
+   Net:   No ethernet found.
+   K230# cpu list
+     0: cpu@0      thead,c908
+   K230# usb start
+   starting USB...
+   Bus usb@91540000: USB DWC2
+   scanning bus usb@91540000 for devices...
+   Warning: r8152_eth (eth0) using random MAC address - 1e:33:97:47:e6:32
+   2 USB Device(s) found
+   K230# usb tree
+   USB device tree:
+     1  Hub (480 Mb/s, 0mA)
+     |   U-Boot Root Hub
+     |
+     +-2  Vendor specific (480 Mb/s, 100mA)
+          Realtek USB 10/100 LAN 000000000000
+
+   K230#

doc/board/index.rst

@@ -21,6 +21,7 @@ Board-specific doc
    beagle/index
    broadcom/index
    bsh/index
+   canaan/index
    cloos/index
    congatec/index
    coolpi/index