[PATCH v2 0/2] board: sophgo: Add support for Milk-V Duo S

[PATCH v2 0/2] board: sophgo: Add support for Milk-V Duo S

[João Paulo Gonçalves]

This series adds support for the Milk-V Duo S, a development board based
on the Sophgo SG2000 SoC with 512 MiB of RAM. The board uses the
upstream Linux devicetree via OF_UPSTREAM.

The Duo S gets its own board directory, based on the Milk-V Duo 256M
one. Apart from the devicetree, the two boards share almost all of their
configuration. However, they use different SoCs (SG2000 vs. SG2002), so
the Duo S is not treated as a variant of the Duo 256M.

Hiago and Andrei reviewed these patches internally before submission,
hence their Acked-by tags. Since they already work with these boards,
they have agreed to maintain the Duo S support.

For now, the documentation improvements (boot flow, FSBL, fip.bin,
OpenSBI requirements) are in the Milk-V Duo S board doc. Since most of
this information is common to all CV18xx/SG200x boards, a follow-up
series will, following Yao Zi's suggestion, move the common parts into a
generic SoC document, referenced by the Milk-V Duo, Duo 256M and Duo S
board docs.

Tested on a Milk-V Duo S.

---
Changes in v2:
- Drop the two devicetree cherry-picks: dts/upstream is now synced to
  v7.3, which already includes the SG2000 dtsi and the Milk-V Duo S
  devicetree
- board: doc: Clarify the OpenSBI version requirement (v1.5 or later)
- board: doc: Describe the boot flow (FSBL, coprocessor firmware,
  OpenSBI, U-Boot) and the fip.bin contents
- board: doc: Fix the fiptool command: pass --text-base to match
  CONFIG_TEXT_BASE and add the required --rtos path
- clk: Drop E Shattow's Reviewed-by as requested
- Link to v1: https://patch.msgid.link/20261016-upstream-v1-milk-duo-s-v1-0-e4bf386eea2d@gmail.com

---
João Paulo Gonçalves (2):
      clk: sophgo: cv1800b: Add SG2000 compatible string
      board: sophgo: Add support for Milk-V Duo S

 arch/riscv/Kconfig                       |   4 +
 board/sophgo/milkv_duo_s/Kconfig         |  30 +++++++
 board/sophgo/milkv_duo_s/MAINTAINERS     |   8 ++
 board/sophgo/milkv_duo_s/Makefile        |   6 ++
 board/sophgo/milkv_duo_s/milkv_duo_s.env |   8 ++
 configs/milkv_duo_s_defconfig            |  43 ++++++++++
 doc/board/sophgo/index.rst               |   1 +
 doc/board/sophgo/milkv_duo_s.rst         | 131 +++++++++++++++++++++++++++++++
 drivers/clk/sophgo/clk-cv1800b.c         |   1 +
 include/configs/milkv_duo_s.h            |  12 +++
 10 files changed, 244 insertions(+)
---
base-commit: f97bb5c1ad78e95856917b92c7270c82d4b11e21
change-id: 20261014-upstream-v1-milk-duo-s-c4d2935c4298

Best regards,
-- 
João Paulo Gonçalves <jpaulo.silvagoncalves@gmail.com>

[PATCH v2 1/2] clk: sophgo: cv1800b: Add SG2000 compatible string

[João Paulo Gonçalves]

The upstream SG2000 devicetree (sg2000.dtsi) uses "sophgo,sg2000-clk" as
the clock controller compatible string. The clocks needed by U-Boot are
the same as on the CV1800, so the existing driver can be reused.

Add "sophgo,sg2000-clk" to the driver match table.

Signed-off-by: João Paulo Gonçalves <jpaulo.silvagoncalves@gmail.com>
---
 drivers/clk/sophgo/clk-cv1800b.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/clk/sophgo/clk-cv1800b.c b/drivers/clk/sophgo/clk-cv1800b.c
index 248a69321fc1..93d71ad1c314 100644
--- a/drivers/clk/sophgo/clk-cv1800b.c
+++ b/drivers/clk/sophgo/clk-cv1800b.c
@@ -744,6 +744,7 @@ const struct clk_ops cv1800b_clk_ops = {
 
 static const struct udevice_id cv1800b_clk_of_match[] = {
 	{ .compatible = "sophgo,cv1800-clk" },
+	{ .compatible = "sophgo,sg2000-clk" },
 	{ },
 };
 

-- 
2.53.0

[PATCH v2 2/2] board: sophgo: Add support for Milk-V Duo S

[João Paulo Gonçalves]

Add support for the Milk-V Duo S, a development board based on the
Sophgo SG2000 SoC with 512 MiB of RAM.

The SG2000 differs from the CV1800B used on the Milk-V Duo 64M and the
SG2002 used on the Milk-V Duo 256M, but these SoCs share most of their
IP blocks, including the CPU core, so the existing CV1800B support can
be reused.

Add a separate board directory, target and defconfig for the Duo S,
based on the Milk-V Duo 256M ones. Like the Duo 256M, it reuses the
common Milk-V Duo board code. The defconfig uses the upstream devicetree
via OF_UPSTREAM.

Link: https://milkv.io/docs/duo/getting-started/duos
Acked-by: Andrei Lalaev <andrey.lalaev@gmail.com>
Acked-by: Hiago De Franco <hfranco@baylibre.com>
Signed-off-by: João Paulo Gonçalves <jpaulo.silvagoncalves@gmail.com>
---
 arch/riscv/Kconfig                       |   4 +
 board/sophgo/milkv_duo_s/Kconfig         |  30 +++++++
 board/sophgo/milkv_duo_s/MAINTAINERS     |   8 ++
 board/sophgo/milkv_duo_s/Makefile        |   6 ++
 board/sophgo/milkv_duo_s/milkv_duo_s.env |   8 ++
 configs/milkv_duo_s_defconfig            |  43 ++++++++++
 doc/board/sophgo/index.rst               |   1 +
 doc/board/sophgo/milkv_duo_s.rst         | 131 +++++++++++++++++++++++++++++++
 include/configs/milkv_duo_s.h            |  12 +++
 9 files changed, 243 insertions(+)

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index 386241efd4a0..df10354e9aef 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -32,6 +32,9 @@ config TARGET_MILKV_DUO
 config TARGET_MILKV_DUO_256M
 	bool "Support Milk-V Duo 256M Board"
 
+config TARGET_MILKV_DUO_S
+	bool "Support Milk-V Duo S Board"
+
 config TARGET_OPENPITON_RISCV64
 	bool "Support RISC-V cores on OpenPiton SoC"
 
@@ -125,6 +128,7 @@ source "board/sifive/unmatched/Kconfig"
 source "board/sipeed/maix/Kconfig"
 source "board/sophgo/milkv_duo/Kconfig"
 source "board/sophgo/milkv_duo_256m/Kconfig"
+source "board/sophgo/milkv_duo_s/Kconfig"
 source "board/sophgo/licheerv_nano/Kconfig"
 source "board/spacemit/k1/Kconfig"
 source "board/spacemit/k3/Kconfig"
diff --git a/board/sophgo/milkv_duo_s/Kconfig b/board/sophgo/milkv_duo_s/Kconfig
new file mode 100644
index 000000000000..6ec6bd65d938
--- /dev/null
+++ b/board/sophgo/milkv_duo_s/Kconfig
@@ -0,0 +1,30 @@
+if TARGET_MILKV_DUO_S
+
+config SYS_BOARD
+	default "milkv_duo_s"
+
+config SYS_VENDOR
+	default "sophgo"
+
+config SYS_CPU
+	default "cv1800b"
+
+config SYS_CONFIG_NAME
+	default "milkv_duo_s"
+
+# The vendor FIP tool prepends a 32-byte loader header to u-boot.bin and loads
+# the result at 0x80200000, so the U-Boot code runs 0x20 bytes above that.
+config TEXT_BASE
+	default 0x80200020
+
+config ENV_SIZE
+	default 0x20000
+
+config ENV_SECT_SIZE
+	default 0x40000
+
+config BOARD_SPECIFIC_OPTIONS
+	def_bool y
+	select SOPHGO_CV1800B
+
+endif
diff --git a/board/sophgo/milkv_duo_s/MAINTAINERS b/board/sophgo/milkv_duo_s/MAINTAINERS
new file mode 100644
index 000000000000..86533c03fd9a
--- /dev/null
+++ b/board/sophgo/milkv_duo_s/MAINTAINERS
@@ -0,0 +1,8 @@
+Milk-V Duo S
+M:	Andrei Lalaev <andrey.lalaev@gmail.com>
+M:	Hiago De Franco <hfranco@baylibre.com>
+S:	Maintained
+F:	board/sophgo/milkv_duo_s/
+F:	configs/milkv_duo_s_defconfig
+F:	doc/board/sophgo/milkv_duo_s.rst
+F:	include/configs/milkv_duo_s.h
diff --git a/board/sophgo/milkv_duo_s/Makefile b/board/sophgo/milkv_duo_s/Makefile
new file mode 100644
index 000000000000..a1b6aaee1489
--- /dev/null
+++ b/board/sophgo/milkv_duo_s/Makefile
@@ -0,0 +1,6 @@
+# SPDX-License-Identifier: GPL-2.0+
+#
+# Copyright (c) 2026, João Paulo Gonçalves <jpaulo.silvagoncalves@gmail.com>
+
+obj-y += ../milkv_duo/board.o
+obj-$(CONFIG_NET_LEGACY) += ../common/ethernet.o
diff --git a/board/sophgo/milkv_duo_s/milkv_duo_s.env b/board/sophgo/milkv_duo_s/milkv_duo_s.env
new file mode 100644
index 000000000000..4c9f53d08118
--- /dev/null
+++ b/board/sophgo/milkv_duo_s/milkv_duo_s.env
@@ -0,0 +1,8 @@
+fdt_addr_r=0x84000000
+fdtfile=DEFAULT_DEVICE_TREE.dtb
+kernel_addr_r=0x80200000
+kernel_comp_addr_r=0x88000000
+kernel_comp_size=0x4000000
+pxefile_addr_r=0x84300000
+ramdisk_addr_r=0x84400000
+scriptaddr=0x84200000
diff --git a/configs/milkv_duo_s_defconfig b/configs/milkv_duo_s_defconfig
new file mode 100644
index 000000000000..41a31c4ad46c
--- /dev/null
+++ b/configs/milkv_duo_s_defconfig
@@ -0,0 +1,43 @@
+CONFIG_RISCV=y
+CONFIG_SYS_MALLOC_LEN=0x820000
+CONFIG_SYS_MALLOC_F_LEN=0x8000
+CONFIG_NR_DRAM_BANKS=1
+CONFIG_HAS_CUSTOM_SYS_INIT_SP_ADDR=y
+CONFIG_CUSTOM_SYS_INIT_SP_ADDR=0x82300000
+CONFIG_DEFAULT_DEVICE_TREE="sophgo/sg2000-milkv-duo-s"
+CONFIG_SYS_LOAD_ADDR=0x80080000
+CONFIG_IDENT_STRING=" milkv_duo_s"
+CONFIG_TARGET_MILKV_DUO_S=y
+CONFIG_ARCH_RV64I=y
+CONFIG_RISCV_SMODE=y
+CONFIG_FIT=y
+CONFIG_BOOTSTD_FULL=y
+# CONFIG_BOOTMETH_EFI_BOOTMGR is not set
+CONFIG_SD_BOOT=y
+CONFIG_SYS_CBSIZE=512
+CONFIG_SYS_PBSIZE=544
+CONFIG_SYS_PROMPT="milkv_duo_s# "
+# CONFIG_CMD_BOOTDEV is not set
+CONFIG_CMD_MBR=y
+CONFIG_CMD_MMC=y
+CONFIG_CMD_POWEROFF=y
+# CONFIG_CMD_MII is not set
+CONFIG_CMD_EXT4_WRITE=y
+# CONFIG_ISO_PARTITION is not set
+# CONFIG_EFI_PARTITION is not set
+CONFIG_OF_UPSTREAM=y
+CONFIG_ENV_OVERWRITE=y
+CONFIG_NET_RANDOM_ETHADDR=y
+CONFIG_CLK_SOPHGO_CV1800B=y
+CONFIG_MMC=y
+CONFIG_MMC_IO_VOLTAGE=y
+CONFIG_MMC_UHS_SUPPORT=y
+CONFIG_MMC_SDHCI=y
+CONFIG_MMC_SDHCI_ADMA=y
+CONFIG_MMC_SDHCI_CV1800B=y
+CONFIG_ETH_DESIGNWARE=y
+CONFIG_SYS_NS16550=y
+CONFIG_SYS_NS16550_MEM32=y
+CONFIG_SPI=y
+CONFIG_SYSRESET=y
+CONFIG_SYSRESET_CV1800B=y
diff --git a/doc/board/sophgo/index.rst b/doc/board/sophgo/index.rst
index 19c9a19b1d4b..61aceafceea3 100644
--- a/doc/board/sophgo/index.rst
+++ b/doc/board/sophgo/index.rst
@@ -7,4 +7,5 @@ Sophgo
 
    milkv_duo
    milkv_duo_256m
+   milkv_duo_s
    licheerv_nano
diff --git a/doc/board/sophgo/milkv_duo_s.rst b/doc/board/sophgo/milkv_duo_s.rst
new file mode 100644
index 000000000000..9f6bf04d1842
--- /dev/null
+++ b/doc/board/sophgo/milkv_duo_s.rst
@@ -0,0 +1,131 @@
+.. SPDX-License-Identifier: GPL-2.0+
+
+Milk-V Duo S
+============
+
+SG2000 RISC-V SoC
+-----------------
+The SG2000 is a high-performance, low-power 64-bit RISC-V/ARM SoC from Sophgo.
+
+Mainline support
+----------------
+Support for the following drivers is already enabled:
+
+1. ns16550 UART Driver.
+2. Synopsys Designware MSHC Driver.
+3. Synopsys Designware Ethernet Controller.
+
+Building
+~~~~~~~~
+1. Add the RISC-V toolchain to your PATH.
+2. Setup ARCH & cross compilation environment variable:
+
+.. code-block:: console
+
+   export CROSS_COMPILE=<riscv64 toolchain prefix>
+   cd <U-Boot-dir>
+   make milkv_duo_s_defconfig
+   make
+
+This will generate u-boot.bin
+
+Boot flow
+~~~~~~~~~
+The board boots from a FIP image, fip.bin, which contains the following
+binaries:
+
+- FSBL (First Stage Boot Loader): the vendor bootloader [1]. It serves the
+  same purpose as U-Boot SPL, but U-Boot does not support SPL for this SoC
+  yet, so the vendor FSBL is required.
+- Coprocessor firmware: the vendor firmware (cvirtos.bin) or custom firmware
+  for the C906L coprocessor. It is not needed to boot U-Boot, but it is
+  required by fiptool.
+- OpenSBI (fw_dynamic.bin), built with the board devicetree.
+- U-Boot (u-boot.bin).
+
+The boot flow is:
+
+1. The boot ROM loads fip.bin from the FAT partition of the SD card and runs
+   the FSBL.
+2. The FSBL initializes the clocks and DRAM, starts the coprocessor firmware
+   on the C906L, and loads OpenSBI and U-Boot into DRAM.
+3. The FSBL jumps to OpenSBI, which runs in M-mode.
+4. OpenSBI starts U-Boot in S-mode.
+
+The fip.bin image is created with the Sophgo fiptool [2], which provides
+prebuilt vendor binaries: data/fsbl/cv181x.bin, the FSBL for the CV181x/SG200x
+SoCs, and data/cvirtos.bin, the coprocessor firmware. The fiptool also requires
+the data/ddr_param.bin file.
+
+Booting
+~~~~~~~
+Currently, we rely on the vendor FSBL to initialize the clock and DRAM, and
+load OpenSBI and the u-boot image, then bootup from it.
+
+To run u-boot.bin on top of FSBL, follow these steps:
+
+1. Generate a compatible u-boot.bin using U-Boot with the Milk-V Duo S
+   default configuration.
+
+2. Use mainline OpenSBI v1.5+ (v1.5 is the first release supporting the SG2000
+   [3]). Use FW_FDT_PATH to point to sg2000-milkv-duo-s.dtb device tree file
+   while compiling fw_dynamic. Example:
+
+.. code-block:: console
+
+   cd <OpenSBI-dir>
+   make PLATFORM=generic FW_FDT_PATH=<U-Boot-dir>/dts/upstream/src/riscv/sophgo/sg2000-milkv-duo-s.dtb
+
+This will generate build/platform/generic/firmware/fw_dynamic.bin.
+
+3. Use the vendor-provided tool [2] to create a unified fip.bin file containing
+   FSBL, coprocessor firmware, OpenSBI, and U-Boot. Note that you will have to
+   use the file cv181x.bin as the FSBL, and that the U-Boot load address must
+   match CONFIG_TEXT_BASE (0x80200020). The tool also requires the
+   data/ddr_param.bin file. Example:
+
+.. code-block:: console
+
+   cd <fiptool-dir>
+   ./fiptool \
+       --fsbl data/fsbl/cv181x.bin \
+       --ddr_param data/ddr_param.bin \
+       --rtos data/cvirtos.bin \
+       --opensbi <OpenSBI-dir>/build/platform/generic/firmware/fw_dynamic.bin \
+       --uboot <U-Boot-dir>/u-boot.bin \
+       --text-base $((0x80200020))
+
+4. Place the generated fip.bin file into the FAT partition of the SD card.
+
+5. Set the board's boot core selection switch to RISC-V.
+
+6. Insert the SD card into the board and power it on.
+
+The board will automatically execute the FSBL from the fip.bin file.
+Subsequently, it will transition to OpenSBI, and finally, OpenSBI will invoke
+U-Boot.
+
+[1]: https://github.com/sophgo/fsbl
+
+[2]: https://github.com/sophgo/fiptool
+
+[3]: https://github.com/riscv-software-src/opensbi/releases/tag/v1.5
+
+Sample boot log from Milk-V Duo S board
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+.. code-block:: none
+
+  U-Boot 2026.10-g3c39950264fd (Oct 23 2026 - 21:28:58 -0300) milkv_duo_s
+
+  DRAM:  512 MiB
+  Core:  28 devices, 13 uclasses, devicetree: separate
+  MMC:   mmc@4310000: 0, mmc@4320000: 2, mmc@4300000: 1
+  Loading Environment from nowhere... OK
+  In:    serial@4140000
+  Out:   serial@4140000
+  Err:   serial@4140000
+  Net:
+  Warning: ethernet@4070000 (eth0) using random MAC address - 4e:27:14:9f:7c:d6
+  eth0: ethernet@4070000
+  Hit any key to stop autoboot: 0
+  milkv_duo_s#
diff --git a/include/configs/milkv_duo_s.h b/include/configs/milkv_duo_s.h
new file mode 100644
index 000000000000..f60aa23fc181
--- /dev/null
+++ b/include/configs/milkv_duo_s.h
@@ -0,0 +1,12 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+/*
+ * Copyright (c) 2026, João Paulo Gonçalves <jpaulo.silvagoncalves@gmail.com>
+ *
+ */
+
+#ifndef __CONFIG_H
+#define __CONFIG_H
+
+#define CFG_SYS_SDRAM_BASE	0x80000000
+
+#endif /* __CONFIG_H */

-- 
2.53.0

Re: [PATCH v2 2/2] board: sophgo: Add support for Milk-V Duo S

[Yao Zi]

On Sun, Oct 25, 2026 at 11:30:24AM -0300, João Paulo Gonçalves wrote:
> Add support for the Milk-V Duo S, a development board based on the
> Sophgo SG2000 SoC with 512 MiB of RAM.
> 
> The SG2000 differs from the CV1800B used on the Milk-V Duo 64M and the
> SG2002 used on the Milk-V Duo 256M, but these SoCs share most of their
> IP blocks, including the CPU core, so the existing CV1800B support can
> be reused.
> 
> Add a separate board directory, target and defconfig for the Duo S,
> based on the Milk-V Duo 256M ones. Like the Duo 256M, it reuses the
> common Milk-V Duo board code. The defconfig uses the upstream devicetree
> via OF_UPSTREAM.
> 
> Link: https://milkv.io/docs/duo/getting-started/duos
> Acked-by: Andrei Lalaev <andrey.lalaev@gmail.com>
> Acked-by: Hiago De Franco <hfranco@baylibre.com>
> Signed-off-by: João Paulo Gonçalves <jpaulo.silvagoncalves@gmail.com>
> ---
>  arch/riscv/Kconfig                       |   4 +
>  board/sophgo/milkv_duo_s/Kconfig         |  30 +++++++
>  board/sophgo/milkv_duo_s/MAINTAINERS     |   8 ++
>  board/sophgo/milkv_duo_s/Makefile        |   6 ++
>  board/sophgo/milkv_duo_s/milkv_duo_s.env |   8 ++
>  configs/milkv_duo_s_defconfig            |  43 ++++++++++
>  doc/board/sophgo/index.rst               |   1 +
>  doc/board/sophgo/milkv_duo_s.rst         | 131 +++++++++++++++++++++++++++++++

Please separate documentation changes into another commit.

>  include/configs/milkv_duo_s.h            |  12 +++
>  9 files changed, 243 insertions(+)

...

> diff --git a/configs/milkv_duo_s_defconfig b/configs/milkv_duo_s_defconfig
> new file mode 100644
> index 000000000000..41a31c4ad46c
> --- /dev/null
> +++ b/configs/milkv_duo_s_defconfig
> @@ -0,0 +1,43 @@
> +CONFIG_RISCV=y
> +CONFIG_SYS_MALLOC_LEN=0x820000
> +CONFIG_SYS_MALLOC_F_LEN=0x8000
> +CONFIG_NR_DRAM_BANKS=1
> +CONFIG_HAS_CUSTOM_SYS_INIT_SP_ADDR=y
> +CONFIG_CUSTOM_SYS_INIT_SP_ADDR=0x82300000
> +CONFIG_DEFAULT_DEVICE_TREE="sophgo/sg2000-milkv-duo-s"
> +CONFIG_SYS_LOAD_ADDR=0x80080000
> +CONFIG_IDENT_STRING=" milkv_duo_s"
> +CONFIG_TARGET_MILKV_DUO_S=y
> +CONFIG_ARCH_RV64I=y
> +CONFIG_RISCV_SMODE=y
> +CONFIG_FIT=y
> +CONFIG_BOOTSTD_FULL=y
> +# CONFIG_BOOTMETH_EFI_BOOTMGR is not set
> +CONFIG_SD_BOOT=y
> +CONFIG_SYS_CBSIZE=512
> +CONFIG_SYS_PBSIZE=544
> +CONFIG_SYS_PROMPT="milkv_duo_s# "
> +# CONFIG_CMD_BOOTDEV is not set
> +CONFIG_CMD_MBR=y
> +CONFIG_CMD_MMC=y
> +CONFIG_CMD_POWEROFF=y
> +# CONFIG_CMD_MII is not set
> +CONFIG_CMD_EXT4_WRITE=y
> +# CONFIG_ISO_PARTITION is not set
> +# CONFIG_EFI_PARTITION is not set

Personally speaking, I prefer to turn on EFI related stuff
(BOOTMETH_EFI_BOOTMGR and EFI_PARTITION). Here EFI is more practical
since Duo-S carries 512MiB RAM, and I do have a device booted through
EFI.

But anyway, it's a embedded device and takes forever to boot a generic
distribution, so what you've done here is fine, too.

...

> diff --git a/doc/board/sophgo/index.rst b/doc/board/sophgo/index.rst
> index 19c9a19b1d4b..61aceafceea3 100644
> --- a/doc/board/sophgo/index.rst
> +++ b/doc/board/sophgo/index.rst
> @@ -7,4 +7,5 @@ Sophgo
>  
>     milkv_duo
>     milkv_duo_256m
> +   milkv_duo_s
>     licheerv_nano
> diff --git a/doc/board/sophgo/milkv_duo_s.rst b/doc/board/sophgo/milkv_duo_s.rst
> new file mode 100644
> index 000000000000..9f6bf04d1842
> --- /dev/null
> +++ b/doc/board/sophgo/milkv_duo_s.rst

...

> +Boot flow
> +~~~~~~~~~
> +The board boots from a FIP image, fip.bin, which contains the following
> +binaries:
> +
> +- FSBL (First Stage Boot Loader): the vendor bootloader [1]. It serves the
> +  same purpose as U-Boot SPL, but U-Boot does not support SPL for this SoC
> +  yet, so the vendor FSBL is required.
> +- Coprocessor firmware: the vendor firmware (cvirtos.bin) or custom firmware
> +  for the C906L coprocessor. It is not needed to boot U-Boot, but it is
> +  required by fiptool.

Please confirm whether this is correct. I remembered the coprocessor
firmware is optional, too.

> +- OpenSBI (fw_dynamic.bin), built with the board devicetree.
> +- U-Boot (u-boot.bin).

...

> +5. Set the board's boot core selection switch to RISC-V.

It'll be nice to describe the exact position of the switch.

...

Regards,
Yao Zi