Subject: [PATCH v2 01/17] ACPI: GTDT: Account for GTDTv3 size when walking the platform timer descriptors

From: Marc Zyngier <[email-masked]>
Date: Thu, 14 May 2026 16:09:29 +0100

Since ARMv8.1, the architecture has grown an EL2-private virtual
timer. This has been described in ACPI since ACPI v6.3 and revision
3 of the GTDT table.

An aditional structure was added in ACPICA, though in a rather
bizarre way, and merged in v5.1 as 8f5a14d053100 ("ACPICA: ACPI 6.3:
add GTDT Revision 3 support").

Finally plug the table parsing in GTDT, and correct the parsing of
the platform timer subtables to account for the expanded size of
the base table.

Suggested-by: Sudeep Holla <[email-masked]>
Signed-off-by: Marc Zyngier <[email-masked]>
---
 drivers/acpi/arm64/gtdt.c | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/drivers/acpi/arm64/gtdt.c b/drivers/acpi/arm64/gtdt.c
index ffc867bac2d60..b9d9b8edf2df7 100644
--- a/drivers/acpi/arm64/gtdt.c
+++ b/drivers/acpi/arm64/gtdt.c
@@ -32,6 +32,12 @@ struct acpi_gtdt_descriptor {
 	struct acpi_table_gtdt *gtdt;
 	void *gtdt_end;
 	void *platform_timer;
+	bool v3;
+};
+
+struct gtdt_v3 {
+	struct acpi_table_gtdt	gtdt_v2;
+	struct acpi_gtdt_el2	el2_vtimer;
 };
 
 static struct acpi_gtdt_descriptor acpi_gtdt_desc __initdata;
@@ -39,8 +45,14 @@ static struct acpi_gtdt_descriptor acpi_gtdt_desc __initdata;
 static __init bool platform_timer_valid(void *platform_timer)
 {
 	struct acpi_gtdt_header *gh = platform_timer;
+	void *platform_timer_begin;
+
+	if (acpi_gtdt_desc.v3)
+		platform_timer_begin = container_of(acpi_gtdt_desc.gtdt, struct gtdt_v3, gtdt_v2) + 1;
+	else
+		platform_timer_begin = acpi_gtdt_desc.gtdt + 1;
 
-	return (platform_timer >= (void *)(acpi_gtdt_desc.gtdt + 1) &&
+	return (platform_timer >= platform_timer_begin &&
 		platform_timer < acpi_gtdt_desc.gtdt_end &&
 		gh->length != 0 &&
 		platform_timer + gh->length <= acpi_gtdt_desc.gtdt_end);
@@ -169,6 +181,7 @@ int __init acpi_gtdt_init(struct acpi_table_header *table,
 	acpi_gtdt_desc.gtdt = gtdt;
 	acpi_gtdt_desc.gtdt_end = (void *)table + table->length;
 	acpi_gtdt_desc.platform_timer = NULL;
+	acpi_gtdt_desc.v3 = gtdt->header.revision >= 3 && gtdt->header.length >= sizeof(struct gtdt_v3);
 	if (platform_timer_count)
 		*platform_timer_count = 0;
 
-- 
2.47.3