linux-kernel - [PATCH v2 2/2] drivers: firmware: dmi_scan: Add support for reading SMBIOS from DT

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Message-ID: <20251022114527.618908-3-adriana@arista.com>
Date: Wed, 22 Oct 2025 04:45:27 -0700
From: adriana <adriana@...sta.com>
To: krzk@...nel.org,
	robh+dt@...nel.org,
	jdelvare@...e.com,
	frowand.list@...il.com
Cc: linux-arm-kernel@...ts.infradread.org,
	linux-kernel@...r.kernel.org,
	devicetree@...r.kernel.org,
	vasilykh@...sta.com,
	adriana@...sta.com
Subject: [PATCH v2 2/2] drivers: firmware: dmi_scan: Add support for reading SMBIOS from DT

Signed-off-by: adriana <adriana@...sta.com>
---
 drivers/firmware/dmi_scan.c | 74 +++++++++++++++++++++++++++++++++++++
 1 file changed, 74 insertions(+)

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)
-- 
2.51.0