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

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Message-ID: <CAERbo5z81zhxzu3+BAd23QzgpFoCMH6-AsYm4sBfoA0YXO3TOg@mail.gmail.com>
Date: Tue, 21 Oct 2025 19:54:23 +0300
From: Adriana Nicolae <adriana@...sta.com>
To: jdelvare@...e.com, linux-kernel@...r.kernel.org
Cc: Vasiliy Khoruzhick <vasilykh@...sta.com>
Subject: Re: [PATCH 1/1] DMI: Scan for DMI tbale from DTS info

Hello maintainers,

Following up on this patch, I was wondering if there have been any
prior discussions or similar requests?

I would also appreciate your feedback on the proposed changes.

Thank you,
Adriana

On Fri, Sep 26, 2025 at 6:56 PM adriana <adriana@...sta.com> wrote:
>
> 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)