[PATCH v5] boot/bootfdt: Add smbios3-entrypoint to FDT for non-EFI boots

[Adriana Nicolae]

From: adriana <adriana at arista.com>

The Linux kernel can discover SMBIOS tables through two primary methods:
1. Via EFI tables, when using EFI boot;
2. Via the 'smbios3-entrypoint' property in the /chosen node of the
device tree.

When U-Boot boots a Linux kernel using a non-EFI command ("bootm",
"bootz", or "booti"), the kernel relies on the device tree to detect
the hardware. If SMBIOS tables are available in U-Boot, they should
be passed to the kernel via this device tree property.

This patch modifies boot_fdt_prepare(), to inject the SMBIOSv3 table
address into the device tree if there is a table generated by U-boot.
The "board_fdt_chosen_smbios" is weak in order to leave the possibilty
for specific boards to select custom SMBIOS addresses.

The changes in this patch are added in the context of supporting this
device tree property in linux kernel:
https://lkml.org/lkml/2025/10/24/1393

Device tree schema was updated to include the "smbios3-entrypoint" node
in pull request: https://github.com/devicetree-org/dt-schema/pull/177

Signed-off-by: Adriana Nicolae <adriana at arista.com>
---
Changes in v5:
  - Allocate 4KiB extra space for fdt blob and align it to 8 bytes.

Changes in v4:
  - Remove weak function board_fdt_chosen_smbios(), replace with
    gd_smbios_start();
  - Return -EAGAIN in test if GENERATE_SMBIOS_TABLE is not enabled;
  - Remove unnecessary fdt cleanup at the end of the test;
  - Added missing newlines at the end of the modified files.

Changes in v3:
  - Moved "board_fdt_chosen_smbios" function to lib/smbios.c
  - Return physical address of smbios entry and use map_sysmem to
    access the entry point;
  - Removed check for config enabled and added check for
    GENERATE_SMBIOS_TABLE;
  - Add test to check that smbios entry address is added into fdt;

Changes in v2:
  - Renamed device tree property to "smbios3-entrypoint".
  - Removed redundant check for CONFIG_SMBIOS.
---
 boot/fdt_support.c | 19 ++++++++++++++++++
 test/dm/fdtdec.c   | 48 ++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 67 insertions(+)

diff --git a/boot/fdt_support.c b/boot/fdt_support.c
index 92f2f534ee0..1c215e548db 100644
--- a/boot/fdt_support.c
+++ b/boot/fdt_support.c
@@ -27,6 +27,7 @@
 #include <fdtdec.h>
 #include <version.h>
 #include <video.h>
+#include <smbios.h>
 
 DECLARE_GLOBAL_DATA_PTR;
 
@@ -333,6 +334,7 @@ int fdt_chosen(void *fdt)
 	int   nodeoffset;
 	int   err;
 	const char *str;		/* used to set string properties */
+	ulong smbiosaddr;		/* SMBIOS table address */
 
 	err = fdt_check_header(fdt);
 	if (err < 0) {
@@ -387,6 +389,23 @@ int fdt_chosen(void *fdt)
 		return err;
 	}
 
+	if (CONFIG_IS_ENABLED(GENERATE_SMBIOS_TABLE)) {
+		/* Inject SMBIOS address when we have a valid address.
+		* This is useful for systems using booti/bootm instead of bootefi.
+		* Failure to set this property is non-fatal, we only generate a
+		* warning.
+		*/
+		smbiosaddr = gd_smbios_start();
+		if (smbiosaddr) {
+			err = fdt_setprop_u64(fdt, nodeoffset, "smbios3-entrypoint",
+					smbiosaddr);
+			if (err < 0) {
+				printf("WARNING: could not set smbios3-entrypoint %s.\n",
+				fdt_strerror(err));
+			}
+		}
+	}
+
 	return fdt_fixup_stdout(fdt, nodeoffset);
 }
 
diff --git a/test/dm/fdtdec.c b/test/dm/fdtdec.c
index 1f24f1d5dff..ea5a494612c 100644
--- a/test/dm/fdtdec.c
+++ b/test/dm/fdtdec.c
@@ -7,6 +7,9 @@
 #include <asm/global_data.h>
 #include <dm/of_extra.h>
 #include <dm/test.h>
+#include <fdt_support.h>
+#include <mapmem.h>
+#include <smbios.h>
 #include <test/ut.h>
 
 DECLARE_GLOBAL_DATA_PTR;
@@ -129,3 +132,48 @@ static int dm_test_fdtdec_add_reserved_memory(struct unit_test_state *uts)
 }
 DM_TEST(dm_test_fdtdec_add_reserved_memory,
 	UTF_SCAN_PDATA | UTF_SCAN_FDT | UTF_FLAT_TREE);
+
+static int dm_test_fdt_chosen_smbios(struct unit_test_state *uts)
+{
+	void *blob;
+	ulong val;
+	struct smbios3_entry *entry;
+	int chosen, blob_sz;
+	const fdt64_t *prop;
+
+	if (!CONFIG_IS_ENABLED(GENERATE_SMBIOS_TABLE)) {
+		return -EAGAIN;
+	}
+
+	blob_sz = fdt_totalsize(gd->fdt_blob) + 4096;
+	blob = memalign(8, blob_sz);
+	ut_assertnonnull(blob);
+
+	/* Make a writable copy of the fdt blob */
+	ut_assertok(fdt_open_into(gd->fdt_blob, blob, blob_sz));
+
+	/* Mock SMBIOS table */
+	entry = map_sysmem(gd->arch.smbios_start, sizeof(struct smbios3_entry));
+	memcpy(entry->anchor, "_SM3_", 5);
+	entry->length = sizeof(struct smbios3_entry);
+	unmap_sysmem(entry);
+
+	/* Force fdt_chosen to run */
+	ut_assertok(fdt_chosen(blob));
+
+	chosen = fdt_path_offset(blob, "/chosen");
+	ut_assert(chosen >= 0);
+
+	/* Verify the property exists */
+	prop = fdt_getprop(blob, chosen, "smbios3-entrypoint", NULL);
+	ut_assertnonnull(prop);
+
+	/* Verify the property matches smbios_start */
+	val = fdt64_to_cpu(*prop);
+	ut_asserteq_64(gd->arch.smbios_start, val);
+
+	free(blob);
+
+	return 0;
+}
+DM_TEST(dm_test_fdt_chosen_smbios, UTF_SCAN_PDATA | UTF_SCAN_FDT);
-- 
2.51.0