[PATCH] docs/system/riscv: sifive_u: Update S-mode U-Boot image build instructions

[Bin Meng]

Currently, the documentation outlines the process for building the
S-mode U-Boot image using `make menuconfig` and manual actions within
the menuconfig UI. However, this approach is fragile due to Kconfig
options potentially changing across different releases. For example,
CONFIG_OF_PRIOR_STAGE has been replaced by CONFIG_BOARD since v2022.01
release, and CONFIG_TEXT_BASE has been moved to the 'General setup'
menu from the 'Boot options' menu in v2024.01 release.

This update aims to make the S-mode U-Boot image build instructions
future-proof. It leverages the 'config' script provided in the U-Boot
source tree to edit the .config file, followed by a `make olddefconfig`.

Validated with U-Boot v2024.01 release.

Signed-off-by: Bin Meng <bmeng@tinylab.org>

---

 docs/system/riscv/sifive_u.rst | 33 ++++++++++++---------------------
 1 file changed, 12 insertions(+), 21 deletions(-)

diff --git a/docs/system/riscv/sifive_u.rst b/docs/system/riscv/sifive_u.rst
index 7b166567f9..8f55ae8e31 100644
--- a/docs/system/riscv/sifive_u.rst
+++ b/docs/system/riscv/sifive_u.rst
@@ -210,7 +210,7 @@ command line options with ``qemu-system-riscv32``.
 Running U-Boot
 --------------
 
-U-Boot mainline v2021.07 release is tested at the time of writing. To build a
+U-Boot mainline v2024.01 release is tested at the time of writing. To build a
 U-Boot mainline bootloader that can be booted by the ``sifive_u`` machine, use
 the sifive_unleashed_defconfig with similar commands as described above for
 Linux:
@@ -325,15 +325,10 @@ configuration of U-Boot:
 
   $ export CROSS_COMPILE=riscv64-linux-
   $ make sifive_unleashed_defconfig
-  $ make menuconfig
-
-then manually select the following configuration:
-
-  * Device Tree Control ---> Provider of DTB for DT Control ---> Prior Stage 
bootloader DTB
-
-and unselect the following configuration:
-
-  * Library routines ---> Allow access to binman information in the device tree
+  $ ./scripts/config --enable OF_BOARD
+  $ ./scripts/config --disable BINMAN_FDT
+  $ ./scripts/config --disable SPL
+  $ make olddefconfig
 
 This changes U-Boot to use the QEMU generated device tree blob, and bypass
 running the U-Boot SPL stage.
@@ -352,17 +347,13 @@ It's possible to create a 32-bit U-Boot S-mode image as 
well.
 
   $ export CROSS_COMPILE=riscv64-linux-
   $ make sifive_unleashed_defconfig
-  $ make menuconfig
-
-then manually update the following configuration in U-Boot:
-
-  * Device Tree Control ---> Provider of DTB for DT Control ---> Prior Stage 
bootloader DTB
-  * RISC-V architecture ---> Base ISA ---> RV32I
-  * Boot options ---> Boot images ---> Text Base ---> 0x80400000
-
-and unselect the following configuration:
-
-  * Library routines ---> Allow access to binman information in the device tree
+  $ ./scripts/config --disable ARCH_RV64I
+  $ ./scripts/config --enable ARCH_RV32I
+  $ ./scripts/config --set-val TEXT_BASE 0x80400000
+  $ ./scripts/config --enable OF_BOARD
+  $ ./scripts/config --disable BINMAN_FDT
+  $ ./scripts/config --disable SPL
+  $ make olddefconfig
 
 Use the same command line options to boot the 32-bit U-Boot S-mode image:
 
-- 
2.34.1