linux-kernel - Re: [PATCH v3 5/5] firmware: dmi: Read additional information when decoding DMI table

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Message-ID: <20260116213032.GC471170@yaz-khff2.amd.com>
Date: Fri, 16 Jan 2026 16:30:32 -0500
From: Yazen Ghannam <yazen.ghannam@....com>
To: "Mario Limonciello (AMD)" <superm1@...nel.org>
Cc: Jean Delvare <jdelvare@...e.com>, linux-kernel@...r.kernel.org,
	Borislav Petkov <bp@...en8.de>
Subject: Re: [PATCH v3 5/5] firmware: dmi: Read additional information when
 decoding DMI table

On Sat, Jan 10, 2026 at 07:48:34AM -0600, Mario Limonciello (AMD) wrote:
> Type 40 entries (Additional information) are summarized in section
> 7.41 as part of the SMBIOS specification.  These entries aren't
> all interesting enough to save, but on some AMD Zen systems the
> AGESA version is stored here and can be useful to save into
> debugging logs for cross referencing issues when reported.
> 

Should have imperative voice.

> Signed-off-by: Mario Limonciello (AMD) <superm1@...nel.org>
> ---
> v3:
>  * Merge patch to show AGESA version (Jean)
>  * Don't save strings (Jean)
>  * Avoid out of bounds (Jean)
> ---
>  drivers/firmware/dmi_scan.c | 32 ++++++++++++++++++++++++++++++++
>  include/linux/dmi.h         |  7 +++++++
>  2 files changed, 39 insertions(+)
> 
> diff --git a/drivers/firmware/dmi_scan.c b/drivers/firmware/dmi_scan.c
> index caa09ddf0dfa7..e1125d011d24b 100644
> --- a/drivers/firmware/dmi_scan.c
> +++ b/drivers/firmware/dmi_scan.c
> @@ -396,6 +396,34 @@ static void __init dmi_save_dev_pciaddr(int instance, int segment, int bus,
>  	list_add(&dev->dev.list, &dmi_devices);
>  }
>  
> +static void __init dmi_scan_additional(const struct dmi_additional_info *info)
> +{
> +	const u8 *data;
> +	int i;
> +
> +	if (!info || info->header.length < 5)
> +		return;
> +
> +	data = info->entries;
> +
> +	for (i = 0; i < info->count; i++) {
> +		u8 string_num = data[i * 5 + 4];
> +		const char *string_ptr;
> +		int len;
> +
> +		string_ptr = dmi_string_nosave(&info->header, string_num);
> +		if (!string_ptr || !*string_ptr)
> +			continue;
> +
> +		len = strlen(string_ptr);
> +		if (len == 0)
> +			continue;
> +
> +		if (!strncmp(string_ptr, "AGESA", 5))
> +			pr_info("%s\n", string_ptr);
> +	}
> +}
> +
>  static void __init dmi_save_extended_devices(const struct dmi_header *dm)
>  {
>  	const char *name;
> @@ -529,8 +557,12 @@ static void __init dmi_decode(const struct dmi_header *dm, void *dummy)
>  	case DMI_ENTRY_IPMI_DEV:
>  		dmi_save_ipmi_device(dm);
>  		break;
> +	case DMI_ENTRY_ADDITIONAL:
> +		dmi_scan_additional((const struct dmi_additional_info *)dm);
> +		break;
>  	case DMI_ENTRY_ONBOARD_DEV_EXT:
>  		dmi_save_extended_devices(dm);
> +		break;
>  	}
>  }
>  
> diff --git a/include/linux/dmi.h b/include/linux/dmi.h
> index 2eedf44e68012..4bb1b7882237f 100644
> --- a/include/linux/dmi.h
> +++ b/include/linux/dmi.h
> @@ -24,6 +24,7 @@ enum dmi_device_type {
>  	DMI_DEV_TYPE_OEM_STRING = -2,
>  	DMI_DEV_TYPE_DEV_ONBOARD = -3,
>  	DMI_DEV_TYPE_DEV_SLOT = -4,
> +	DMI_DEV_TYPE_ADDITIONAL = -5,
>  };
>  
>  enum dmi_entry_type {
> @@ -91,6 +92,12 @@ struct dmi_device {
>  	void *device_data;	/* Type specific data */
>  };
>  
> +struct dmi_additional_info {
> +	struct dmi_header header;
> +	u8 count;
> +	u8 entries[];
> +} __packed;

This is wrong. The "entries" are not u8. They are structs with this
format:
	Table 119 – Additional Information Entry format

struct dmi_additional_info_entry {
	u8 length;
	u16 handle;
	u8 offset;
	u8 string
	/* Variable length "Value" */
} __packed; 

ACPI tables do this a lot. So there are examples of iterating over
variable length entries.

Thanks,
Yazen