linux-kernel - [PATCH v4 2/2] drivers: firmware: dmi_scan: Add support for reading SMBIOS from DT

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Message-ID: <20251031101009.704759-3-adriana@arista.com>
Date: Fri, 31 Oct 2025 03:10:09 -0700
From: adriana <adriana@...sta.com>
To: ilias.apalodimas@...aro.org,
	ardb@...nel.org,
	trini@...sulko.com
Cc: robh@...nel.org,
	krzk@...nel.org,
	jdelvare@...e.com,
	frowand.list@...il.com,
	linux-kernel@...r.kernel.org,
	devicetree@...r.kernel.org,
	vasilykh@...sta.com,
	arm.ebbr-discuss@....com,
	boot-architecture@...ts.linaro.org,
	linux-efi@...r.kernel.org,
	uefi-discuss@...ts.uefi.org,
	linux-arm-kernel@...ts.infradead.org,
	adriana <adriana@...sta.com>
Subject: [PATCH v4 2/2] drivers: firmware: dmi_scan: Add support for reading SMBIOS from DT

Some bootloaders provide SMBIOS/DMI tables at a specific memory address,
particularly on non-EFI ARM platforms. The kernel's standard EFI DMI
scanner cannot find these tables.

This patch adds a fallback mechanism to the DMI scanner to read the
physical address of the SMBIOS3 entry point from the device tree.

This scan is performed only if the standard EFI check fails.

Signed-off-by: adriana <adriana@...sta.com>
---
 drivers/firmware/dmi_scan.c | 54 +++++++++++++++++++++++++++++++++++++
 1 file changed, 54 insertions(+)

diff --git a/drivers/firmware/dmi_scan.c b/drivers/firmware/dmi_scan.c
index 70d39adf50dc..c29ca98f09b5 100644
--- a/drivers/firmware/dmi_scan.c
+++ b/drivers/firmware/dmi_scan.c
@@ -10,10 +10,12 @@
 #include <linux/random.h>
 #include <asm/dmi.h>
 #include <linux/unaligned.h>
+#include <linux/of.h>
 
 #ifndef SMBIOS_ENTRY_POINT_SCAN_START
 #define SMBIOS_ENTRY_POINT_SCAN_START 0xF0000
 #endif
+#define SMBIOS3_ENTRY_POINT_SIZE 32
 
 struct kobject *dmi_kobj;
 EXPORT_SYMBOL_GPL(dmi_kobj);
@@ -670,6 +672,51 @@ static int __init dmi_smbios3_present(const u8 *buf)
 	return 1;
 }
 
+/**
+ * dmi_scan_from_dt - Find SMBIOS3 entrypoint address via Device Tree
+ *
+ * Checks if the bootloader has passed the physical address of the
+ * SMBIOS3 entrypoint structure via the "linux,smbios3-entrypoint"
+ * property in the /chosen node.
+ * Returns true if a valid entrypoint is found.
+ */
+static bool __init dmi_scan_from_dt(void)
+{
+	struct device_node *chosen;
+	const __be64 *prop;
+	char buf[SMBIOS3_ENTRY_POINT_SIZE];
+	void __iomem *p;
+	bool dmi_available = false;
+	u64 addr;
+	int len;
+
+	if(!IS_ENABLED(CONFIG_OF))
+		return false;
+
+	chosen = of_find_node_by_path("/chosen");
+	if (!chosen)
+		return false;
+
+	prop = of_get_property(chosen, "linux,smbios3-entrypoint", &len);
+	if (prop && len >= sizeof(u64)) {
+		addr = be64_to_cpup(prop);
+
+		p = dmi_early_remap(addr, SMBIOS3_ENTRY_POINT_SIZE);
+		if (!p)
+			goto out;
+
+		memcpy_fromio(buf, p, sizeof(buf));
+		dmi_early_unmap(p, SMBIOS3_ENTRY_POINT_SIZE);
+
+		if (!dmi_smbios3_present(buf))
+			dmi_available = true;
+	}
+
+out:
+	of_node_put(chosen);
+	return dmi_available;
+}
+
 static void __init dmi_scan_machine(void)
 {
 	char __iomem *p, *q;
@@ -718,6 +765,13 @@ static void __init dmi_scan_machine(void)
 			dmi_available = 1;
 			return;
 		}
+	} else if (dmi_scan_from_dt()) {
+		/*
+		 * If EFI is not present or failed, try getting SMBIOS3
+		 * entrypoint from the Device Tree.
+		 */
+		dmi_available = 1;
+		return;
 	} else if (IS_ENABLED(CONFIG_DMI_SCAN_MACHINE_NON_EFI_FALLBACK)) {
 		p = dmi_early_remap(SMBIOS_ENTRY_POINT_SCAN_START, 0x10000);
 		if (p == NULL)
-- 
2.51.0