[Buildroot] [PATCH v4 9/9] board: Document Canaan K210 based boards support

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+# Canaan Kendryte K210 SoC Based Board Support
+
+Buildroot provides support for Canaan RISC-V Kendryte K210 SoC based boards.
+Configurations for different K210 Soc board variants are available. The boards
+supported are as follows.
+
+* From Sipeed: MAIX Bit, MAIX Dock (Dan Dock), MAIX Go and MAIXDUINO boards.
+
+* From Canaan: KD233 development board.
+
+For each board, two configurations are provided:
+
+* Configuration to build a bootable kernel image with built-in initramfs root
+file system (SD card is not used)
+
+* Configuration to build a bootable kernel image with the root file system
+on the board SD card.
+
+In all cases, the build process generates a bootable kernel image that can be
+directly flashed to the board boot flash. A boot loader (e.g. U-Boot) and
+OpenSBI are not necessary.
+
+## Bootable Kernel Image With A Built-In Initramfs Root File System
+
+The following table lists the default configuration provided for each board
+supported.
+
+| Board vendor and model | configuration name          |
+| ---------------------- | --------------------------- |
+| Canaan KD233           | canaan_kd233_defconfig      |
+| Sipeed MAIX bit        | sipeed_maix_bit_defconfig   |
+| Sipeed MAIX Go         | sipeed_maix_go_defconfig    |
+| Sipeed MAIX dock       | sipeed_maix_dock_defconfig  |
+| Sipeed MAIXDUINO       | sipeed_maixduino_defconfig  |
+
+The build procedure is similar for all boards. The steps to create the kernel
+bootable image are as follows:
+
+```
+$ make <config name>
+$ make
+```
+
+The build process will generate the bootable binary image file
+*output/images/loader.bin*. This image file must be written to the board boot
+flash using the
+[Sipeed kflash python utility](https://github.com/sipeed/kflash.py).
+
+```
+$ sudo python3 kflash.py -p /dev/ttyUSB0 -b 1500000 -t output/images/loader.bin
+```
+
+The above command will open a terminal console and reboot the board once the
+image is written. The output will be similar to the following (example obtained
+with the Sipeed MAIX Bit board).
+
+```
+[INFO] COM Port Selected Manually:  /dev/ttyUSB0
+[INFO] Default baudrate is 115200 , later it may be changed to the value you set.
+[INFO] Trying to Enter the ISP Mode...
+._
+[INFO] Automatically detected goE/kd233
+
+[INFO] Greeting Message Detected, Start Downloading ISP
+Downloading ISP: |=================================================================| 100.0% 10kiB/s
+[INFO] Booting From 0x80000000
+[INFO] Wait For 0.1 second for ISP to Boot
+[INFO] Boot to Flashmode Successfully
+[INFO] Selected Baudrate:  1500000
+[INFO] Baudrate changed, greeting with ISP again ...
+[INFO] Boot to Flashmode Successfully
+[INFO] Selected Flash:  On-Board
+[INFO] Initialization flash Successfully
+Programming BIN: |=================================================================| 100.0% 50kiB/s
+[INFO] Rebooting...
+--- forcing DTR inactive
+--- forcing RTS inactive
+--- Miniterm on /dev/ttyUSB0  115200,8,N,1 ---
+--- Quit: Ctrl+] | Menu: Ctrl+T | Help: Ctrl+T followed by Ctrl+H ---
+[    0.000000] Linux version 5.13.0 (xxx@yyy.com) (riscv64-buildroot-linux-uclibc-gcc.br_real (Buildroot 2021.05-rc3-447-g26fab79296-dirty) 11.1.0, GNU ld (GNU Binutils) 2.32) #2 SMP Fri Jul 9 10:59:05 JST 2021
+[    0.000000] Machine model: SiPeed MAIX BiT
+[    0.000000] earlycon: sifive0 at MMIO 0x0000000038000000 (options '115200n8')
+[    0.000000] printk: bootconsole [sifive0] enabled
+[    0.000000] Zone ranges:
+[    0.000000]   DMA32    [mem 0x0000000080000000-0x00000000807fffff]
+[    0.000000]   Normal   empty
+[    0.000000] Movable zone start for each node
+[    0.000000] Early memory node ranges
+[    0.000000]   node   0: [mem 0x0000000080000000-0x00000000807fffff]
+[    0.000000] Initmem setup node 0 [mem 0x0000000080000000-0x00000000807fffff]
+[    0.000000] riscv: ISA extensions acdfim
+[    0.000000] riscv: ELF capabilities acdfim
+[    0.000000] percpu: max_distance=0x18000 too large for vmalloc space 0x0
+[    0.000000] percpu: Embedded 12 pages/cpu s19360 r0 d29792 u49152
+[    0.000000] Built 1 zonelists, mobility grouping off.  Total pages: 2020
+[    0.000000] Kernel command line: earlycon console=ttySIF0
+[    0.000000] Dentry cache hash table entries: 1024 (order: 1, 8192 bytes, linear)
+[    0.000000] Inode-cache hash table entries: 512 (order: 0, 4096 bytes, linear)
+[    0.000000] mem auto-init: stack:off, heap alloc:off, heap free:off
+[    0.000000] Memory: 6052K/8192K available (950K kernel code, 140K rwdata, 200K rodata, 480K init, 66K bss, 2140K reserved, 0K cma-reserved)
+[    0.000000] rcu: Hierarchical RCU implementation.
+[    0.000000] rcu: RCU calculated value of scheduler-enlistment delay is 25 jiffies.
+[    0.000000] NR_IRQS: 64, nr_irqs: 64, preallocated irqs: 0
+[    0.000000] riscv-intc: 64 local interrupts mapped
+[    0.000000] plic: interrupt-controller@c000000: mapped 65 interrupts with 2 handlers for 2 contexts.
+[    0.000000] k210-clk: clock-controller: CPU running at 390 MHz
+[    0.000000] clint: timer@2000000: timer running at 7800000 Hz
+[    0.000000] clocksource: clint_clocksource: mask: 0xffffffffffffffff max_cycles: 0x3990be68b, max_idle_ns: 881590404272 ns
+[    0.000002] sched_clock: 64 bits at 7MHz, resolution 128ns, wraps every 4398046511054ns
+[    0.008183] Calibrating delay loop (skipped), value calculated using timer frequency.. 15.60 BogoMIPS (lpj=31200)
+[    0.018250] pid_max: default: 4096 minimum: 301
+[    0.022865] Mount-cache hash table entries: 512 (order: 0, 4096 bytes, linear)
+[    0.029971] Mountpoint-cache hash table entries: 512 (order: 0, 4096 bytes, linear)
+[    0.040316] rcu: Hierarchical SRCU implementation.
+[    0.045151] smp: Bringing up secondary CPUs ...
+[    0.050271] smp: Brought up 1 node, 2 CPUs
+[    0.054355] devtmpfs: initialized
+[    0.071852] clocksource: jiffies: mask: 0xffffffff max_cycles: 0xffffffff, max_idle_ns: 7645041785100000 ns
+[    0.080926] pinctrl core: initialized pinctrl subsystem
+[    0.117980] clocksource: Switched to clocksource clint_clocksource
+[    0.130392] workingset: timestamp_bits=62 max_order=11 bucket_order=0
+[    0.162498] k210-fpioa 502b0000.pinmux: K210 FPIOA pin controller
+[    0.175231] k210-sysctl 50440000.syscon: K210 system controller
+[    0.182048] k210-rst 50440000.syscon:reset-controller: K210 reset controller
+[    0.189335] 38000000.serial: ttySIF0 at MMIO 0x38000000 (irq = 1, base_baud = 115200) is a SiFive UART v0
+[    0.198258] printk: console [ttySIF0] enabled
+[    0.198258] printk: console [ttySIF0] enabled
+[    0.206899] printk: bootconsole [sifive0] disabled
+[    0.206899] printk: bootconsole [sifive0] disabled
+[    0.218821] cacheinfo: Unable to detect cache hierarchy for CPU 0
+[    0.236193] i2c /dev entries driver
+[    0.240804] random: get_random_bytes called from 0x000000008000586e with crng_init=0
+[    0.253005] Freeing unused kernel memory: 476K
+[    0.256754] This architecture does not have kernel memory protection.
+[    0.263177] Run /init as init process
+          __  _
+         / / (_) ____   _   _ __  __
+        / /  | ||  _ \ | | | |\ \/ /
+       / /___| || | | || |_| | >  <
+      /_____/|_||_| |_| \____|/_/\_\
+        RISC-V Kendryte K210 NOMMU
+
+
+BusyBox v1.33.1 (2021-07-09 10:58:24 JST) hush - the humble shell
+Enter 'help' for a list of built-in commands.
+
+/ #
+```
+
+To open a console without re-flashing the board, *miniterm.py* can be used.
+```
+sudo miniterm.py --raw --eol=LF /dev/ttyUSB0 115200
+```
+
+The options *--raw --eol=LF* are added here to avoid a double carriage return
+each time a command is entered.
+
+## Bootable Kernel Image With the Root File System On SD Card
+
+The following table lists the default configurations provided for the supported
+boards.
+
+| Board vendor and model | configuration name                 |
+| ---------------------- | ---------------------------------- |
+| Canaan KD233           | canaan_kd233_sdcard_defconfig      |
+| Sipeed MAIX bit        | sipeed_maix_bit_sdcard_defconfig   |
+| Sipeed MAIX Go         | sipeed_maix_go_sdcard_defconfig    |
+| Sipeed MAIX dock       | sipeed_maix_dock_sdcard_defconfig  |
+| Sipeed MAIXDUINO       | sipeed_maixduino_sdcard_defconfig  |
+
+The build procedure is similar to the built-in initramfs case.
+
+```
+$ make <config name>
+$ make
+```
+
+The build process will generate two files under the *output/images* directory.
+
+* *loader.bin*: This bootable kernel image file.
+
+* *rootfs.ext2*: ext2 (rev1) SD card image.
+
+Before flashing the kernel bootable image, the SD card must be prepared.
+
+```
+$ sudo dd if=output/images/rootfs.ext2 of=/dev/sdX1 bs=1M
+$ sync
+$ eject /dev/sdX
+```
+
+Where */dev/sdX* is the device file name of the SD card. The SD card must have
+at least one partition of at least 60 MB. Once completed, the SD card can be
+inserted into the board and the kernel bootable image file written to the board
+boot flash, using
+[Sipeed kflash python utility](https://github.com/sipeed/kflash.py).
+
+```
+$ sudo python3 kflash.py -p /dev/ttyUSB0 -b 1500000 -t output/image/loader.bin
+```
+
+The above command will open a terminal console and reboot the board once the
+image is written. The output will be similar to the following (example obtained
+with the Sipeed MAIX Bit board).
+
+```
+[INFO] COM Port Selected Manually:  /dev/ttyUSB0 
+[INFO] Default baudrate is 115200 , later it may be changed to the value you set. 
+[INFO] Trying to Enter the ISP Mode... 
+._
+[INFO] Automatically detected goE/kd233 
+
+[INFO] Greeting Message Detected, Start Downloading ISP 
+Downloading ISP: |=================================================================| 100.0% 10kiB/s
+[INFO] Booting From 0x80000000 
+[INFO] Wait For 0.1 second for ISP to Boot 
+[INFO] Boot to Flashmode Successfully 
+[INFO] Selected Baudrate:  1500000 
+[INFO] Baudrate changed, greeting with ISP again ...  
+[INFO] Boot to Flashmode Successfully 
+[INFO] Selected Flash:  On-Board 
+[INFO] Initialization flash Successfully 
+Programming BIN: |=================================================================| 100.0% 50kiB/s
+[INFO] Rebooting... 
+--- forcing DTR inactive
+--- forcing RTS inactive
+--- Miniterm on /dev/ttyUSB0  115200,8,N,1 ---
+--- Quit: Ctrl+] | Menu: Ctrl+T | Help: Ctrl+T followed by Ctrl+H ---
+[    0.000000] Linux version 5.13.0 (damien@twashi.fujisawa.hgst.com) (riscv64-buildroot-linux-uclibc-gcc.br_real (Buildroot 2021.05-rc3-447-g26fab79296-dirty) 11.1.0, GNU ld (GNU Binutils) 2.32) #1 SMP Fri Jul 9 14:50:18 JST 2021
+[    0.000000] Machine model: SiPeed MAIX BiT
+[    0.000000] earlycon: sifive0 at MMIO 0x0000000038000000 (options '115200n8')
+[    0.000000] printk: bootconsole [sifive0] enabled
+[    0.000000] Zone ranges:
+[    0.000000]   DMA32    [mem 0x0000000080000000-0x00000000807fffff]
+[    0.000000]   Normal   empty
+[    0.000000] Movable zone start for each node
+[    0.000000] Early memory node ranges
+[    0.000000]   node   0: [mem 0x0000000080000000-0x00000000807fffff]
+[    0.000000] Initmem setup node 0 [mem 0x0000000080000000-0x00000000807fffff]
+[    0.000000] riscv: ISA extensions acdfim
+[    0.000000] riscv: ELF capabilities acdfim
+[    0.000000] percpu: max_distance=0x18000 too large for vmalloc space 0x0
+[    0.000000] percpu: Embedded 12 pages/cpu s19488 r0 d29664 u49152
+[    0.000000] Built 1 zonelists, mobility grouping off.  Total pages: 2020
+[    0.000000] Kernel command line: earlycon console=ttySIF0 rootdelay=2 root=/dev/mmcblk0p1 ro
+[    0.000000] Dentry cache hash table entries: 1024 (order: 1, 8192 bytes, linear)
+[    0.000000] Inode-cache hash table entries: 512 (order: 0, 4096 bytes, linear)
+[    0.000000] mem auto-init: stack:off, heap alloc:off, heap free:off
+[    0.000000] Memory: 6184K/8192K available (1149K kernel code, 151K rwdata, 232K rodata, 105K init, 69K bss, 2008K reserved, 0K cma-reserved)
+[    0.000000] rcu: Hierarchical RCU implementation.
+[    0.000000] rcu: RCU calculated value of scheduler-enlistment delay is 25 jiffies.
+[    0.000000] NR_IRQS: 64, nr_irqs: 64, preallocated irqs: 0
+[    0.000000] riscv-intc: 64 local interrupts mapped
+[    0.000000] plic: interrupt-controller@c000000: mapped 65 interrupts with 2 handlers for 2 contexts.
+[    0.000000] k210-clk: clock-controller: CPU running at 390 MHz
+[    0.000000] clint: timer@2000000: timer running at 7800000 Hz
+[    0.000000] clocksource: clint_clocksource: mask: 0xffffffffffffffff max_cycles: 0x3990be68b, max_idle_ns: 881590404272 ns
+[    0.000001] sched_clock: 64 bits at 7MHz, resolution 128ns, wraps every 4398046511054ns
+[    0.008179] Calibrating delay loop (skipped), value calculated using timer frequency.. 15.60 BogoMIPS (lpj=31200)
+[    0.018252] pid_max: default: 4096 minimum: 301
+[    0.022859] Mount-cache hash table entries: 512 (order: 0, 4096 bytes, linear)
+[    0.029972] Mountpoint-cache hash table entries: 512 (order: 0, 4096 bytes, linear)
+[    0.040382] rcu: Hierarchical SRCU implementation.
+[    0.045234] smp: Bringing up secondary CPUs ...
+[    0.050345] smp: Brought up 1 node, 2 CPUs
+[    0.054419] devtmpfs: initialized
+[    0.071317] clocksource: jiffies: mask: 0xffffffff max_cycles: 0xffffffff, max_idle_ns: 7645041785100000 ns
+[    0.080392] pinctrl core: initialized pinctrl subsystem
+[    0.119377] clocksource: Switched to clocksource clint_clocksource
+[    0.131238] workingset: timestamp_bits=62 max_order=11 bucket_order=0
+[    0.159389] k210-fpioa 502b0000.pinmux: K210 FPIOA pin controller
+[    0.171494] k210-sysctl 50440000.syscon: K210 system controller
+[    0.178193] k210-rst 50440000.syscon:reset-controller: K210 reset controller
+[    0.186800] 38000000.serial: ttySIF0 at MMIO 0x38000000 (irq = 1, base_baud = 115200) is a SiFive UART v0
+[    0.195764] printk: console [ttySIF0] enabled
+[    0.195764] printk: console [ttySIF0] enabled
+[    0.204377] printk: bootconsole [sifive0] disabled
+[    0.204377] printk: bootconsole [sifive0] disabled
+[    0.216056] cacheinfo: Unable to detect cache hierarchy for CPU 0
+[    0.232882] i2c /dev entries driver
+[    0.263551] mmc_spi spi2.0: SD/MMC host mmc0, no WP, no poweroff, cd polling
+[    0.271167] random: get_random_bytes called from 0x0000000080005d60 with crng_init=0
+[    0.289511] Waiting 2 sec before mounting root device...
+[    0.312217] mmc0: host does not support reading read-only switch, assuming write-enable
+[    0.319565] mmc0: new SDHC card on SPI
+[    0.326205] mmcblk0: mmc0:0000 SA16G 14.5 GiB 
+[    0.333339] random: fast init done
+[    0.337935]  mmcblk0: p1 p2
+[    2.311900] VFS: Mounted root (ext2 filesystem) readonly on device 179:1.
+[    2.321555] devtmpfs: mounted
+[    2.324099] Freeing unused kernel memory: 100K
+[    2.328227] This architecture does not have kernel memory protection.
+[    2.334652] Run /sbin/init as init process
+[    2.491565] random: crng init done
+          __  _
+         / / (_) ____   _   _ __  __
+        / /  | ||  _ \ | | | |\ \/ /
+       / /___| || | | || |_| | >  < 
+      /_____/|_||_| |_| \____|/_/\_\
+        RISC-V Kendryte K210 NOMMU
+
+
+BusyBox v1.33.1 (2021-07-09 10:58:24 JST) hush - the humble shell
+Enter 'help' for a list of built-in commands.
+
+/ # 
+```
+
+Of note is that the kernel command line arguments, specified in the kernel
+*nommu_k210_sdcard* default configuration, mount the SD card as read-only to
+avoid corruptions of the ext2 root file system. This is recommended as this
+board does not isupport clean shutdown or halt.
+
+Similarly to the initramfs build case, a console can be open without
+re-flashing the board using *miniterm.py*.
+```
+sudo miniterm.py --raw --eol=LF /dev/ttyUSB0 115200
+```

@@ -0,0 +1,4 @@
+# Canaan KD233 Board
+
+See the common documentation for
+[Canaan K210 SoC based boards](../k210-common/README.md).

@@ -0,0 +1,4 @@
+# Sipeed MAIX-Bit Board
+
+See the common documentation for
+[Canaan K210 SoC based boards](../../canaan/k210-common/README.md).

@@ -0,0 +1,4 @@
+# Sipeed MAIX-Dock Board
+
+See the common documentation for
+[Canaan K210 SoC based boards](../../canaan/k210-common/README.md).

@@ -0,0 +1,4 @@
+# Sipeed MAIX-Go Board
+
+See the common documentation for
+[Canaan K210 SoC based boards](../../canaan/k210-common/README.md).

@@ -0,0 +1,4 @@
+# Sipeed MAIXDUINO Board
+
+See the common documentation for
+[Canaan K210 SoC based boards](../../canaan/k210-common/README.md).