diff --git a/include/acpi/actbl3.h b/include/acpi/actbl3.h
index 41ad9648ca52..787bcc814463 100644
--- a/include/acpi/actbl3.h
+++ b/include/acpi/actbl3.h
@@ -448,7 +448,8 @@ struct acpi_table_pcct {
 
 enum acpi_pcct_type {
 	ACPI_PCCT_TYPE_GENERIC_SUBSPACE = 0,
-	ACPI_PCCT_TYPE_RESERVED = 1	/* 1 and greater are reserved */
+	ACPI_PCCT_TYPE_HW_REDUCED_SUBSPACE = 1,
+	ACPI_PCCT_TYPE_RESERVED = 2	/* 2 and greater are reserved */
 };
 
 /*
@@ -470,6 +471,28 @@ struct acpi_pcct_subspace {
 	u16 min_turnaround_time;
 };
 
+/* 1: HW-reduced Communications Subspace (ACPI 5.1) */
+
+struct acpi_pcct_hw_reduced {
+	struct acpi_subtable_header header;
+	u32 doorbell_interrupt;
+	u8 flags;
+	u8 reserved;
+	u64 base_address;
+	u64 length;
+	struct acpi_generic_address doorbell_register;
+	u64 preserve_mask;
+	u64 write_mask;
+	u32 latency;
+	u32 max_access_rate;
+	u16 min_turnaround_time;
+};
+
+/* Values for doorbell flags above */
+
+#define ACPI_PCCT_INTERRUPT_POLARITY    (1)
+#define ACPI_PCCT_INTERRUPT_MODE        (1<<1)
+
 /*
  * PCC memory structures (not part of the ACPI table)
  */