riscv: do not set default fdt for VisionFive 2

Currently in set_fdtfile() we set the value of environment variable fdtfile
unconditionally. The implies that a value in the environment will be
ignored.

With the patch environment variable fdtfile will only be set if it does not
yet exist. This requires that CONFIG_DEFAULT_FDT_FILE is not set.

Now the user can either set and save fdtfile interactively or in the U-Boot
configuration to overrule the device-tree name chosen based on the
hardware in set_fdtfile().

Reported-by: E Shattow <lucent@gmail.com>
Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Reviewed-by: Leo Yu-Chi Liang <ycliang@andestech.com>

board/starfive/visionfive2/starfive_visionfive2.c

@@ -49,6 +49,10 @@ static void set_fdtfile(void)
 	u8 version;
 	const char *fdtfile;
 
+	fdtfile = env_get("fdtfile");
+	if (fdtfile)
+		return;
+
 	version = get_pcb_revision_from_eeprom();
 	switch (version) {
 	case 'a':

configs/starfive_visionfive2_defconfig

@@ -40,7 +40,6 @@ CONFIG_USE_BOOTARGS=y
 CONFIG_BOOTARGS="console=ttyS0,115200 debug rootwait earlycon=sbi"
 CONFIG_USE_PREBOOT=y
 CONFIG_PREBOOT="nvme scan; usb start; setenv fdt_addr ${fdtcontroladdr}; fdt addr ${fdtcontroladdr};"
-CONFIG_DEFAULT_FDT_FILE="starfive/jh7110-starfive-visionfive-2.dtb"
 CONFIG_SYS_CBSIZE=256
 CONFIG_SYS_PBSIZE=276
 CONFIG_DISPLAY_CPUINFO=y

doc/board/starfive/visionfive2.rst

@@ -71,6 +71,24 @@ Now build the U-Boot SPL and U-Boot proper
 This will generate the U-Boot SPL image (spl/u-boot-spl.bin.normal.out) as well
 as the FIT image (u-boot.itb) with OpenSBI and U-Boot.
 
+Device-tree selection
+~~~~~~~~~~~~~~~~~~~~~
+
+Depending on the board version U-Boot set variable $fdtfile to either
+starfive/jh7110-starfive-visionfive-2-v1.2a.dtb or
+starfive/jh7110-starfive-visionfive-2-v1.3b.dtb.
+
+To overrule this selection the variable can be set manually and saved in the
+environment
+
+::
+
+    setenv fdtfile my_device-tree.dtb
+    env save
+
+or the configuration variable CONFIG_DEFAULT_FDT_FILE can be used to provide
+a default value.
+
 Flashing
 ~~~~~~~~