docs: system: arm: Introduce bananapi_m2u

Add documents for Banana Pi M2U

Signed-off-by: qianfan Zhao <qianfanguijin@163.com>
Reviewed-by: Niek Linnenbank <nieklinnenbank@gmail.com>
[PMM: Minor format fixes to correct sphinx errors]
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

docs/system/arm/bananapi_m2u.rst

@@ -0,0 +1,139 @@
+Banana Pi BPI-M2U (``bpim2u``)
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Banana Pi BPI-M2 Ultra is a quad-core mini single board computer built with
+Allwinner A40i/R40/V40 SoC. It features 2GB of RAM and 8GB eMMC. It also
+has onboard WiFi and BT. On the ports side, the BPI-M2 Ultra has 2 USB A
+2.0 ports, 1 USB OTG port, 1 HDMI port, 1 audio jack, a DC power port,
+and last but not least, a SATA port.
+
+Supported devices
+"""""""""""""""""
+
+The Banana Pi M2U machine supports the following devices:
+
+ * SMP (Quad Core Cortex-A7)
+ * Generic Interrupt Controller configuration
+ * SRAM mappings
+ * SDRAM controller
+ * Timer device (re-used from Allwinner A10)
+ * UART
+ * SD/MMC storage controller
+ * EMAC ethernet
+ * GMAC ethernet
+ * Clock Control Unit
+ * TWI (I2C)
+
+Limitations
+"""""""""""
+
+Currently, Banana Pi M2U does *not* support the following features:
+
+- Graphical output via HDMI, GPU and/or the Display Engine
+- Audio output
+- Hardware Watchdog
+- Real Time Clock
+- USB 2.0 interfaces
+
+Also see the 'unimplemented' array in the Allwinner R40 SoC module
+for a complete list of unimplemented I/O devices: ``./hw/arm/allwinner-r40.c``
+
+Boot options
+""""""""""""
+
+The Banana Pi M2U machine can start using the standard -kernel functionality
+for loading a Linux kernel or ELF executable. Additionally, the Banana Pi M2U
+machine can also emulate the BootROM which is present on an actual Allwinner R40
+based SoC, which loads the bootloader from a SD card, specified via the -sd
+argument to qemu-system-arm.
+
+Running mainline Linux
+""""""""""""""""""""""
+
+To build a Linux mainline kernel that can be booted by the Banana Pi M2U machine,
+simply configure the kernel using the sunxi_defconfig configuration:
+
+.. code-block:: bash
+
+  $ ARCH=arm CROSS_COMPILE=arm-linux-gnueabi- make mrproper
+  $ ARCH=arm CROSS_COMPILE=arm-linux-gnueabi- make sunxi_defconfig
+
+To boot the newly build linux kernel in QEMU with the Banana Pi M2U machine, use:
+
+.. code-block:: bash
+
+  $ qemu-system-arm -M bpim2u -nographic \
+      -kernel /path/to/linux/arch/arm/boot/zImage \
+      -append 'console=ttyS0,115200' \
+      -dtb /path/to/linux/arch/arm/boot/dts/sun8i-r40-bananapi-m2-ultra.dtb
+
+Banana Pi M2U images
+""""""""""""""""""""
+
+Note that the mainline kernel does not have a root filesystem. You can choose
+to build you own image with buildroot using the bananapi_m2_ultra_defconfig.
+Also see https://buildroot.org for more information.
+
+Another possibility is to run an OpenWrt image for Banana Pi M2U which
+can be downloaded from:
+
+   https://downloads.openwrt.org/releases/22.03.3/targets/sunxi/cortexa7/
+
+When using an image as an SD card, it must be resized to a power of two. This can be
+done with the ``qemu-img`` command. It is recommended to only increase the image size
+instead of shrinking it to a power of two, to avoid loss of data. For example,
+to prepare a downloaded Armbian image, first extract it and then increase
+its size to one gigabyte as follows:
+
+.. code-block:: bash
+
+  $ qemu-img resize \
+    openwrt-22.03.3-sunxi-cortexa7-sinovoip_bananapi-m2-ultra-ext4-sdcard.img \
+    1G
+
+Instead of providing a custom Linux kernel via the -kernel command you may also
+choose to let the Banana Pi M2U machine load the bootloader from SD card, just like
+a real board would do using the BootROM. Simply pass the selected image via the -sd
+argument and remove the -kernel, -append, -dbt and -initrd arguments:
+
+.. code-block:: bash
+
+  $ qemu-system-arm -M bpim2u -nic user -nographic \
+    -sd openwrt-22.03.3-sunxi-cortexa7-sinovoip_bananapi-m2-ultra-ext4-sdcard.img
+
+Running U-Boot
+""""""""""""""
+
+U-Boot mainline can be build and configured using the Bananapi_M2_Ultra_defconfig
+using similar commands as describe above for Linux. Note that it is recommended
+for development/testing to select the following configuration setting in U-Boot:
+
+  Device Tree Control > Provider for DTB for DT Control > Embedded DTB
+
+The BootROM of allwinner R40 loading u-boot from the 8KiB offset of sdcard.
+Let's create an bootable disk image:
+
+.. code-block:: bash
+
+  $ dd if=/dev/zero of=sd.img bs=32M count=1
+  $ dd if=u-boot-sunxi-with-spl.bin of=sd.img bs=1k seek=8 conv=notrunc
+
+And then boot it.
+
+.. code-block:: bash
+
+  $ qemu-system-arm -M bpim2u -nographic -sd sd.img
+
+Banana Pi M2U integration tests
+"""""""""""""""""""""""""""""""
+
+The Banana Pi M2U machine has several integration tests included.
+To run the whole set of tests, build QEMU from source and simply
+provide the following command:
+
+.. code-block:: bash
+
+  $ cd qemu-build-dir
+  $ AVOCADO_ALLOW_LARGE_STORAGE=yes tests/venv/bin/avocado \
+    --verbose --show=app,console run -t machine:bpim2u \
+    ../tests/avocado/boot_linux_console.py

docs/system/target-arm.rst

@@ -83,6 +83,7 @@ undocumented; you can get a complete list by running
    arm/versatile
    arm/vexpress
    arm/aspeed
+   arm/bananapi_m2u.rst
    arm/sabrelite
    arm/digic
    arm/cubieboard