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[PATCH v3 2/2] drivers: firmware: dmi_scan: Add support for reading SMBIOS from DT

adriana posted 2 patches 3 months, 1 week ago
There is a newer version of this series
[PATCH v3 2/2] drivers: firmware: dmi_scan: Add support for reading SMBIOS from DT
Posted by adriana 3 months, 1 week ago 
From: Adriana Nicolae <adriana@arista.com>

Signed-off-by: Adriana Nicolae <adriana@arista.com>
---
 drivers/firmware/dmi_scan.c | 58 +++++++++++++++++++++++++++++++++++++
 1 file changed, 58 insertions(+)

diff --git a/drivers/firmware/dmi_scan.c b/drivers/firmware/dmi_scan.c
index 70d39adf50dc..acc0e18b8d0f 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 +673,54 @@ 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;
+
+	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;
+		}
+	}
+
+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 +769,13 @@ 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
Re: [PATCH v3 2/2] drivers: firmware: dmi_scan: Add support for reading SMBIOS from DT
Posted by Ilias Apalodimas 3 months, 1 week ago 
Hi Adriana,

On Fri, 31 Oct 2025 at 10:41, adriana <adriana@arista.com> wrote:
>
> From: Adriana Nicolae <adriana@arista.com>

We'll need a description of why the change is needed here.

[...]

>
>  #ifndef SMBIOS_ENTRY_POINT_SCAN_START
>  #define SMBIOS_ENTRY_POINT_SCAN_START 0xF0000
> @@ -670,6 +673,54 @@ 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;
> +
> +       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);

Please put '32' into a define that explains what it is

> +               if (p == NULL)

I think if (!p) is preferred

> +                       goto out;
> +
> +               memcpy_fromio(buf, p, sizeof(buf));
> +               dmi_early_unmap(p, 32);
> +
> +               if (!dmi_smbios3_present(buf)) {
> +                       dmi_available = true;
> +                       goto out;
> +               }
> +       }
> +
> +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 +769,13 @@ static void __init dmi_scan_machine(void)
>                         dmi_available = 1;
>                         return;
>                 }
> +       } else if (IS_ENABLED(CONFIG_OF) && dmi_scan_from_dt()) {

Can you fold the IS_ENABLED() in dmi_scan_from_dt() please?

> +               /*
[...]

Thanks
/Ilias
Re: [PATCH v3 2/2] drivers: firmware: dmi_scan: Add support for reading SMBIOS from DT
Posted by Ard Biesheuvel 3 months, 1 week ago 
Hello Adriana,

On Fri, 31 Oct 2025 at 09:41, adriana <adriana@arista.com> wrote:
>
> From: Adriana Nicolae <adriana@arista.com>
>
> Signed-off-by: Adriana Nicolae <adriana@arista.com>
> ---
>  drivers/firmware/dmi_scan.c | 58 +++++++++++++++++++++++++++++++++++++
>  1 file changed, 58 insertions(+)
>
> diff --git a/drivers/firmware/dmi_scan.c b/drivers/firmware/dmi_scan.c
> index 70d39adf50dc..acc0e18b8d0f 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 +673,54 @@ 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.

Not sure what 'the standard kernel DT bindings' are, or what you mean
by 'a fixed 32-byte mapping. You could just drop this sentence, I
think, or otherwise, describe that the DT property gives us the
physical address of the SMBIOS3 entrypoint structure.

> + * Returns true if a valid table is found and successfully parsed.

if a valid entry point is found

> + */
> +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;
> +
> +       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;
> +               }
> +       }
> +
> +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 +769,13 @@ static void __init dmi_scan_machine(void)
>                         dmi_available = 1;
>                         return;
>                 }
> +       } else if (IS_ENABLED(CONFIG_OF) && dmi_scan_from_dt()) {

Please drop the IS_ENABLED() here, and fold it into dmi_scan_from_dt(), by doing

if (!IS_ENABLED(CONFIG_OF))
    return false;

at the beginning. This removes the need to provide two different
versions 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
>

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