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Message-ID: <3f427986-1d7a-49b1-b661-e5004f1c7f0d@kernel.org>
Date: Tue, 20 Jan 2026 15:55:54 -0600
From: Mario Limonciello <superm1@...nel.org>
To: Yazen Ghannam <yazen.ghannam@....com>
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 1/20/26 3:45 PM, Yazen Ghannam wrote:
> On Fri, Jan 16, 2026 at 04:30:32PM -0500, Yazen Ghannam wrote:
>> On Sat, Jan 10, 2026 at 07:48:34AM -0600, Mario Limonciello (AMD) wrote:
>>
>
> [...]
>
>> ACPI tables do this a lot. So there are examples of iterating over
>> variable length entries.
>
> Here's another implementation. What do you think?
Oh you beat me to it, been busy this week.
I do like that we can localize the printing code to amd.c. I'll test it
and let you know if it works.
If it does; I'll roll it into the series.
>
> Thanks,
> Yazen
>
>
> From c76f27e5d55570bb25bcefc3365fb3a1852bcad3 Mon Sep 17 00:00:00 2001
> From: Yazen Ghannam <yazen.ghannam@....com>
> Date: Mon, 19 Jan 2026 18:33:09 +0000
> Subject: [PATCH] x86/CPU/AMD: Print AGESA string from DMI additional
> information entry
>
> Type 40 entries (Additional Information) are summarized in section 7.41
> as part of the SMBIOS specification. Generally, these entries aren't
> interesting to save.
>
> However on some AMD Zen systems, the AGESA version is stored here. This
> is useful to save to the kernel message logs for debugging. It can be
> used to cross-reference issues.
>
> Implement an iterator for the Additional Information entries. Use this
> to find and print the AGESA string. Do so in AMD code, since the use
> case is AMD-specific.
>
> Originally-by: "Mario Limonciello (AMD)" <superm1@...nel.org>
> Signed-off-by: Yazen Ghannam <yazen.ghannam@....com>
> ---
> arch/x86/kernel/cpu/amd.c | 53 +++++++++++++++++++++++++++++++++++++
> drivers/firmware/dmi_scan.c | 3 ++-
> include/linux/dmi.h | 18 +++++++++++++
> 3 files changed, 73 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
> index bc94ff1e250a..aa04a27aeb10 100644
> --- a/arch/x86/kernel/cpu/amd.c
> +++ b/arch/x86/kernel/cpu/amd.c
> @@ -1,6 +1,7 @@
> // SPDX-License-Identifier: GPL-2.0-only
> #include <linux/export.h>
> #include <linux/bitops.h>
> +#include <linux/dmi.h>
> #include <linux/elf.h>
> #include <linux/mm.h>
> #include <linux/kvm_types.h>
> @@ -1404,3 +1405,55 @@ static __init int print_s5_reset_status_mmio(void)
> return 0;
> }
> late_initcall(print_s5_reset_status_mmio);
> +
> +static void __init amd_dmi_scan_additional(const struct dmi_header *d, void *p)
> +{
> + struct dmi_a_info *info = (struct dmi_a_info *)d;
> + void *next, *end;
> +
> + /*
> + * DMI Additional Info table has a 'count' field. But it's not very
> + * helpful since the entries are variable length. So don't use it.
> + */
> + if (info->header.type != DMI_ENTRY_ADDITIONAL ||
> + info->header.length < DMI_A_INFO_MIN_SIZE)
> + return;
> +
> + /*
> + * Get the first entry.
> + * The minimum table size guarantees at least one entry is present.
> + */
> + next = (void *)(info + 1);
> + end = (void *)info + info->header.length;
> +
> + do {
> + struct dmi_a_info_entry *entry;
> + const char *string_ptr;
> +
> + entry = (struct dmi_a_info_entry *)next;
> +
> + /*
> + * Not much can be done to validate data. At least the entry
> + * length shouldn't be 0.
> + */
> + if (!entry->length)
> + return;
> +
> + string_ptr = dmi_string_nosave(&info->header, entry->str_num);
> +
> + /* Only one AGESA string is expected. */
> + if (!strncmp(string_ptr, "AGESA", 5)) {
> + pr_info("%s\n", string_ptr);
> + break;
> + }
> +
> + next += entry->length;
> + } while (end - next >= DMI_A_INFO_ENT_MIN_SIZE);
> +}
> +
> +static __init int print_dmi_agesa(void)
> +{
> + dmi_walk(amd_dmi_scan_additional, NULL);
> + return 0;
> +}
> +late_initcall(print_dmi_agesa);
> diff --git a/drivers/firmware/dmi_scan.c b/drivers/firmware/dmi_scan.c
> index caa09ddf0dfa..8b196992618d 100644
> --- a/drivers/firmware/dmi_scan.c
> +++ b/drivers/firmware/dmi_scan.c
> @@ -47,7 +47,7 @@ static struct dmi_memdev_info {
> static int dmi_memdev_nr;
> static int dmi_memdev_populated_nr __initdata;
>
> -static const char * __init dmi_string_nosave(const struct dmi_header *dm, u8 s)
> +const char *dmi_string_nosave(const struct dmi_header *dm, u8 s)
> {
> const u8 *bp = ((u8 *) dm) + dm->length;
> const u8 *nsp;
> @@ -66,6 +66,7 @@ static const char * __init dmi_string_nosave(const struct dmi_header *dm, u8 s)
>
> return dmi_empty_string;
> }
> +EXPORT_SYMBOL_GPL(dmi_string_nosave);
>
> static const char * __init dmi_string(const struct dmi_header *dm, u8 s)
> {
> diff --git a/include/linux/dmi.h b/include/linux/dmi.h
> index 2eedf44e6801..48691d589b88 100644
> --- a/include/linux/dmi.h
> +++ b/include/linux/dmi.h
> @@ -91,6 +91,21 @@ struct dmi_device {
> void *device_data; /* Type specific data */
> };
>
> +#define DMI_A_INFO_ENT_MIN_SIZE 0x6
> +struct dmi_a_info_entry {
> + u8 length;
> + u16 handle;
> + u8 offset;
> + u8 str_num;
> + u8 value[];
> +} __packed;
> +
> +#define DMI_A_INFO_MIN_SIZE 0xB
> +struct dmi_a_info {
> + struct dmi_header header;
> + u8 count;
> +} __packed;
> +
> #ifdef CONFIG_DMI
>
> struct dmi_dev_onboard {
> @@ -120,6 +135,7 @@ extern void dmi_memdev_name(u16 handle, const char **bank, const char **device);
> extern u64 dmi_memdev_size(u16 handle);
> extern u8 dmi_memdev_type(u16 handle);
> extern u16 dmi_memdev_handle(int slot);
> +const char *dmi_string_nosave(const struct dmi_header *dm, u8 s);
>
> #else
>
> @@ -153,6 +169,8 @@ static inline u8 dmi_memdev_type(u16 handle) { return 0x0; }
> static inline u16 dmi_memdev_handle(int slot) { return 0xffff; }
> static inline const struct dmi_system_id *
> dmi_first_match(const struct dmi_system_id *list) { return NULL; }
> +static inline const char *
> + dmi_string_nosave(const struct dmi_header *dm, u8 s) { return NULL; }
>
> #endif
>
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