Re: [PATCH v4 6/6] x86/CPU/AMD: Print AGESA string from DMI additional information entry

["Mario Limonciello (AMD) (kernel.org)" <superm1@kernel.org>]

On 1/21/2026 8:26 AM, Yazen Ghannam wrote:
> On Wed, Jan 21, 2026 at 12:04:31AM -0600, Mario Limonciello (AMD) wrote:
>> From: Yazen Ghannam <yazen.ghannam@amd.com>
>>
>> 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.
>>
>> Signed-off-by: Yazen Ghannam <yazen.ghannam@amd.com>
>> Co-developed-by: "Mario Limonciello (AMD)" <superm1@kernel.org>
>> Signed-off-by: "Mario Limonciello (AMD)" <superm1@kernel.org>
>> ---
>> v4:
>>   * New patch (based upon older versions though)
>> ---
>>   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 c19c4ee74dd1f..5cd60855a85b0 100644
>> --- a/arch/x86/kernel/cpu/amd.c
>> +++ b/arch/x86/kernel/cpu/amd.c
>> @@ -3,6 +3,7 @@
>>   
>>   #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>
>> @@ -1406,3 +1407,55 @@ 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 ed6235ac576b6..a3f7dabd49554 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 2eedf44e68012..b7865fa387ccb 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 dmi_empty_string; }
>>   
> 
> The dmi_empty_string needs to be moved to this header file from
> dmi_scan.c.
> 
> Otherwise, there's a build issue as the test bot reported.
> 
> Thanks,
> Yazen

Yeah; it makes sense now.  Will move in next version.