linux-kernel - [PATCH 1/1] DMI: Scan for DMI tbale from DTS info

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Message-ID: <20250926155612.2737443-1-adriana@arista.com>
Date: Fri, 26 Sep 2025 08:56:12 -0700
From: adriana <adriana@...sta.com>
To: jdelvare@...e.com,
	linux-kernel@...r.kernel.org
Cc: Adriana Nicolae <adriana@...sta.com>
Subject: [PATCH 1/1] DMI: Scan for DMI tbale from DTS info

Allow DMI decoding to use custom addresses stored in Device Tree

Some bootloaders like U-boot, particularly for the ARM architecture,
provide SMBIOS/DMI tables at a specific memory address. However, these
systems often do not boot using a full UEFI environment, which means the
kernel's standard EFI DMI scanner cannot find these tables.

The bootloader can specify the physical addresses of the SMBIOS and
SMBIOS3 tables in the /chosen node using the "linux,smbios-table" and
linux,smbios3-table properties. This patch hooks into the DMI
initialization process to read these properties, map the tables,
and parse the DMI information.

This extra scan is performed after the standard EFI check fails but
before the fallback memory scan, not to alter the order of DMI scanning
for current implementation.

Signed-off-by: Adriana Nicolae <adriana@...sta.com>

diff --git a/drivers/firmware/dmi_scan.c b/drivers/firmware/dmi_scan.c
index 70d39adf50dc..ea3ed40d0370 100644
--- a/drivers/firmware/dmi_scan.c
+++ b/drivers/firmware/dmi_scan.c
@@ -10,6 +10,9 @@
 #include <linux/random.h>
 #include <asm/dmi.h>
 #include <linux/unaligned.h>
+#if IS_ENABLED(CONFIG_OF)
+#include <linux/of.h>
+#endif
 
 #ifndef SMBIOS_ENTRY_POINT_SCAN_START
 #define SMBIOS_ENTRY_POINT_SCAN_START 0xF0000
@@ -670,6 +673,70 @@ static int __init dmi_smbios3_present(const u8 *buf)
 	return 1;
 }
 
+#if IS_ENABLED(CONFIG_OF)
+/**
+ * dmi_scan_from_dt - Find and parse DMI/SMBIOS tables from the Device Tree
+ *
+ * Checks if the bootloader has passed SMBIOS table addresses via the /chosen
+ * node in the Device Tree. This follows the standard kernel DT bindings and
+ * assumes a fixed 32-byte mapping for the entry point.
+ * Returns true if a valid table is found and successfully parsed.
+ */
+static bool __init dmi_scan_from_dt(void)
+{
+	struct device_node *chosen;
+	const __be64 *prop;
+	char buf[32];
+	void __iomem *p;
+	bool dmi_available = false;
+	u64 addr;
+	int len;
+
+	chosen = of_find_node_by_path("/chosen");
+	if (!chosen)
+		return false;
+
+	/* SMBIOSv3 (64-bit entry point) has priority */
+	prop = of_get_property(chosen, "linux,smbios3-table", &len);
+	if (prop && len >= sizeof(u64)) {
+		addr = be64_to_cpup(prop);
+
+		p = dmi_early_remap(addr, 32);
+		if (p == NULL)
+			goto out;
+
+		memcpy_fromio(buf, p, sizeof(buf));
+		dmi_early_unmap(p, 32);
+
+		if (!dmi_smbios3_present(buf)) {
+			dmi_available = true;
+			goto out;
+		}
+	}
+
+	prop = of_get_property(chosen, "linux,smbios-table", &len);
+	if (prop && len >= sizeof(u64)) {
+		addr = be64_to_cpup(prop);
+
+		p = dmi_early_remap(addr, 32);
+		if (p == NULL)
+			goto out;
+
+		memcpy_fromio(buf, p, sizeof(buf));
+		dmi_early_unmap(p, 32);
+
+		if (!dmi_present(buf))
+			dmi_available = true;
+	}
+
+out:
+	of_node_put(chosen);
+	return dmi_available;
+}
+#else
+static bool __init dmi_scan_from_dt(void) { return false; }
+#endif /* IS_ENABLED(CONFIG_OF) */
+
 static void __init dmi_scan_machine(void)
 {
 	char __iomem *p, *q;
@@ -718,6 +785,13 @@ static void __init dmi_scan_machine(void)
 			dmi_available = 1;
 			return;
 		}
+	} else if (IS_ENABLED(CONFIG_OF) && dmi_scan_from_dt()) {
+		/*
+		 * If EFI is not present or failed, try getting SMBIOS
+		 * tables 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)