ACPI / x86: Add support for LPS0 callback handler

Currenty the latest thing run during a suspend to idle attempt is
the LPS0 `prepare_late` callback and the earliest thing is the
`resume_early` callback.

There is a desire for the `amd-pmc` driver to suspend later in the
suspend process (ideally the very last thing), so create a callback
that it or any other driver can hook into to do this.

Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Link: https://lore.kernel.org/r/20220317141445.6498-1-mario.limonciello@amd.com
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>

drivers/acpi/x86/s2idle.c

@@ -86,6 +86,8 @@ struct lpi_device_constraint_amd {
 	int min_dstate;
 };
 
+static LIST_HEAD(lps0_s2idle_devops_head);
+
 static struct lpi_constraints *lpi_constraints_table;
 static int lpi_constraints_table_size;
 static int rev_id;
@@ -444,6 +446,8 @@ static struct acpi_scan_handler lps0_handler = {
 
 int acpi_s2idle_prepare_late(void)
 {
+	struct acpi_s2idle_dev_ops *handler;
+
 	if (!lps0_device_handle || sleep_no_lps0)
 		return 0;
 
@@ -474,14 +478,26 @@ int acpi_s2idle_prepare_late(void)
 		acpi_sleep_run_lps0_dsm(ACPI_LPS0_MS_ENTRY,
 				lps0_dsm_func_mask_microsoft, lps0_dsm_guid_microsoft);
 	}
+
+	list_for_each_entry(handler, &lps0_s2idle_devops_head, list_node) {
+		if (handler->prepare)
+			handler->prepare();
+	}
+
 	return 0;
 }
 
 void acpi_s2idle_restore_early(void)
 {
+	struct acpi_s2idle_dev_ops *handler;
+
 	if (!lps0_device_handle || sleep_no_lps0)
 		return;
 
+	list_for_each_entry(handler, &lps0_s2idle_devops_head, list_node)
+		if (handler->restore)
+			handler->restore();
+
 	/* Modern standby exit */
 	if (lps0_dsm_func_mask_microsoft > 0)
 		acpi_sleep_run_lps0_dsm(ACPI_LPS0_MS_EXIT,
@@ -524,4 +540,28 @@ void acpi_s2idle_setup(void)
 	s2idle_set_ops(&acpi_s2idle_ops_lps0);
 }
 
+int acpi_register_lps0_dev(struct acpi_s2idle_dev_ops *arg)
+{
+	if (!lps0_device_handle || sleep_no_lps0)
+		return -ENODEV;
+
+	lock_system_sleep();
+	list_add(&arg->list_node, &lps0_s2idle_devops_head);
+	unlock_system_sleep();
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(acpi_register_lps0_dev);
+
+void acpi_unregister_lps0_dev(struct acpi_s2idle_dev_ops *arg)
+{
+	if (!lps0_device_handle || sleep_no_lps0)
+		return;
+
+	lock_system_sleep();
+	list_del(&arg->list_node);
+	unlock_system_sleep();
+}
+EXPORT_SYMBOL_GPL(acpi_unregister_lps0_dev);
+
 #endif /* CONFIG_SUSPEND */

include/linux/acpi.h

@@ -1023,7 +1023,15 @@ void acpi_os_set_prepare_extended_sleep(int (*func)(u8 sleep_state,
 
 acpi_status acpi_os_prepare_extended_sleep(u8 sleep_state,
 					   u32 val_a, u32 val_b);
-
+#ifdef CONFIG_X86
+struct acpi_s2idle_dev_ops {
+	struct list_head list_node;
+	void (*prepare)(void);
+	void (*restore)(void);
+};
+int acpi_register_lps0_dev(struct acpi_s2idle_dev_ops *arg);
+void acpi_unregister_lps0_dev(struct acpi_s2idle_dev_ops *arg);
+#endif /* CONFIG_X86 */
 #ifndef CONFIG_IA64
 void arch_reserve_mem_area(acpi_physical_address addr, size_t size);
 #else