riscv: K210: Add a built-in device tree

The K210's bootloader does not provide a device tree. Give the ability
to providea builtin one with the SOC_KENDRYTE_K210_BUILTIN_DTB option.
If selected, this option result in the definition of a builtin DTB
entry in the k210 sysctl driver.

If defined, the builtin DTB entry points to the default k210.dts device
tree file and is keyed with the vendor ID 0x4B5, the arch ID
0xE59889E6A5A04149 ("Canaan AI" in UTF-8 coded Chinese) and the impl ID
0x4D41495832303030 ("MAIX200"). These values are reported by the SiPEED
MAIXDUINO board, the SiPEED MAIX Go board and the SiPEED Dan Dock board.

[Thanks to Damien for the K210 IDs]
Signed-off-by: Damien Le Moal <[e-mail]>
Signed-off-by: Palmer Dabbelt <[e-mail]>

arch/riscv/Kconfig.socs

···
 config SOC_KENDRYTE
 	bool "Kendryte K210 SoC"
 	depends on !MMU
-	select BUILTIN_DTB
 	select SERIAL_SIFIVE if TTY
 	select SERIAL_SIFIVE_CONSOLE if TTY
 	select SIFIVE_PLIC
 	help
 	  This enables support for Kendryte K210 SoC platform hardware.
+
+config SOC_KENDRYTE_K210_DTB
+	def_bool y
+	depends on SOC_KENDRYTE_K210_DTB_BUILTIN
+
+config SOC_KENDRYTE_K210_DTB_BUILTIN
+	bool "Builtin device tree for the Kendryte K210"
+	depends on SOC_KENDRYTE
+	default y
+	select OF
+	select BUILTIN_DTB
+	select SOC_KENDRYTE_K210_DTB
+	help
+	  Builds a device tree for the Kendryte K210 into the Linux image.
+	  This option should be selected if no bootloader is being used.
+	  If unsure, say Y.
 
 endmenu

arch/riscv/boot/dts/Makefile

···
 # SPDX-License-Identifier: GPL-2.0
 subdir-y += sifive
 subdir-y += kendryte
+
+obj-$(CONFIG_BUILTIN_DTB) := $(addsuffix /, $(subdir-y))

arch/riscv/boot/dts/kendryte/Makefile

···
 # SPDX-License-Identifier: GPL-2.0
-dtb-$(CONFIG_SOC_KENDRYTE) += k210.dtb
+dtb-$(CONFIG_SOC_KENDRYTE_K210_DTB) += k210.dtb
+
+obj-$(CONFIG_SOC_KENDRYTE_K210_DTB_BUILTIN) += $(addsuffix .o, $(dtb-y))

drivers/soc/kendryte/k210-sysctl.c

···
 	iounmap(regs);
 }
 SOC_EARLY_INIT_DECLARE(generic_k210, "kendryte,k210", k210_soc_early_init);
+
+#ifdef CONFIG_SOC_KENDRYTE_K210_DTB_BUILTIN
+/*
+ * Generic entry for the default k210.dtb embedded DTB for boards with:
+ *   - Vendor ID: 0x4B5
+ *   - Arch ID: 0xE59889E6A5A04149 (= "Canaan AI" in UTF-8 encoded Chinese)
+ *   - Impl ID:	0x4D41495832303030 (= "MAIX2000")
+ * These values are reported by the SiPEED MAXDUINO, SiPEED MAIX GO and
+ * SiPEED Dan dock boards.
+ */
+SOC_BUILTIN_DTB_DECLARE(k210, 0x4B5, 0xE59889E6A5A04149, 0x4D41495832303030);
+#endif