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

[Heinrich Schuchardt]

On 11/20/25 09:50, Adriana Nicolae wrote:
> 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>

Reviewed-by: Heinrich Schuchardt <xypron.glpk at gmx.de>

> ---
> 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);