[PATCH] boot: add support for fdt_fixup command in environment

[Matthias Schiffer]

The "fdt" command is convenient for making small changes to the OS FDT,
especially during development. This is easy when the kernel and FDT are
loaded separately, but can be cumbersome for FIT images, requiring to
unpack the image, manually apply overlays, etc.

Add an option to execute a command "fdt_fixup" from the environment at
the beginning of image_setup_libfdt() (after overlays are applied, and
before the other fixups).

Signed-off-by: Matthias Schiffer <matthias.schiffer at ew.tq-group.com>
---
 boot/Kconfig     |  9 +++++++++
 boot/image-fdt.c | 19 +++++++++++++++++--
 2 files changed, 26 insertions(+), 2 deletions(-)

diff --git a/boot/Kconfig b/boot/Kconfig
index ef71883a502..7eea935f490 100644
--- a/boot/Kconfig
+++ b/boot/Kconfig
@@ -1502,6 +1502,15 @@ if OF_LIBFDT
 
 menu "Devicetree fixup"
 
+config OF_ENV_SETUP
+	bool "Run a command from environment to set up device tree before boot"
+	depends on CMD_FDT
+	help
+	  This causes U-Boot to run a command from the environment variable
+	  fdt_fixup before booting into the operating system, which can use the
+	  fdt command to modify the device tree. The device tree is then passed
+	  to the OS.
+
 config OF_BOARD_SETUP
 	bool "Set up board-specific details in device tree before boot"
 	help
diff --git a/boot/image-fdt.c b/boot/image-fdt.c
index f10200f6474..78b5c639381 100644
--- a/boot/image-fdt.c
+++ b/boot/image-fdt.c
@@ -9,6 +9,7 @@
  */
 
 #include <common.h>
+#include <command.h>
 #include <fdt_support.h>
 #include <fdtdec.h>
 #include <env.h>
@@ -608,8 +609,22 @@ int image_setup_libfdt(struct bootm_headers *images, void *blob,
 {
 	ulong *initrd_start = &images->initrd_start;
 	ulong *initrd_end = &images->initrd_end;
-	int ret = -EPERM;
-	int fdt_ret;
+	int ret, fdt_ret;
+
+	if (IS_ENABLED(CONFIG_OF_ENV_SETUP)) {
+		const char *fdt_fixup;
+
+		fdt_fixup = env_get("fdt_fixup");
+		if (fdt_fixup) {
+			set_working_fdt_addr(map_to_sysmem(blob));
+			ret = run_command_list(fdt_fixup, -1, 0);
+			if (ret)
+				printf("WARNING: fdt_fixup command returned %d\n",
+				       ret);
+		}
+	}
+
+	ret = -EPERM;
 
 	if (fdt_root(blob) < 0) {
 		printf("ERROR: root node setup failed\n");
-- 
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https://www.tq-group.com/