ACPI: processor: Simplify initial onlining to use same path for cold and hotplug

Separate code paths, combined with a flag set in acpi_processor.c to
indicate a struct acpi_processor was for a hotplugged CPU ensured that
per CPU data was only set up the first time that a CPU was initialized.
This appears to be unnecessary as the paths can be combined by letting
the online logic also handle any CPUs online at the time of driver load.

Motivation for this change, beyond simplification, is that ARM64
virtual CPU HP uses the same code paths for hotplug and cold path in
acpi_processor.c so had no easy way to set the flag for hotplug only.
Removing this necessity will enable ARM64 vCPU HP to reuse the existing
code paths.
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: Hanjun Guo <guohanjun@huawei.com>
Tested-by: Miguel Luis <miguel.luis@oracle.com>
Reviewed-by: Gavin Shan <gshan@redhat.com>
Reviewed-by: Miguel Luis <miguel.luis@oracle.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Link: https://lore.kernel.org/r/20240529133446.28446-2-Jonathan.Cameron@huawei.comSigned-off-by: Catalin Marinas <catalin.marinas@arm.com>

drivers/acpi/acpi_processor.c

@@ -211,12 +211,11 @@ static int acpi_processor_hotadd_init(struct acpi_processor *pr)
 	}
 
 	/*
-	 * CPU got hot-added, but cpu_data is not initialized yet.  Set a flag
-	 * to delay cpu_idle/throttling initialization and do it when the CPU
-	 * gets online for the first time.
+	 * CPU got hot-added, but cpu_data is not initialized yet. Do
+	 * cpu_idle/throttling initialization when the CPU gets online for
+	 * the first time.
 	 */
 	pr_info("CPU%d has been hot-added\n", pr->id);
-	pr->flags.need_hotplug_init = 1;
 
 out:
 	cpus_write_unlock();

drivers/acpi/processor_driver.c

@@ -33,7 +33,6 @@ MODULE_AUTHOR("Paul Diefenbaugh");
 MODULE_DESCRIPTION("ACPI Processor Driver");
 MODULE_LICENSE("GPL");
 
-static int acpi_processor_start(struct device *dev);
 static int acpi_processor_stop(struct device *dev);
 
 static const struct acpi_device_id processor_device_ids[] = {
@@ -47,7 +46,6 @@ static struct device_driver acpi_processor_driver = {
 	.name = "processor",
 	.bus = &cpu_subsys,
 	.acpi_match_table = processor_device_ids,
-	.probe = acpi_processor_start,
 	.remove = acpi_processor_stop,
 };
 
@@ -115,12 +113,9 @@ static int acpi_soft_cpu_online(unsigned int cpu)
 	 * CPU got physically hotplugged and onlined for the first time:
 	 * Initialize missing things.
 	 */
-	if (pr->flags.need_hotplug_init) {
+	if (!pr->flags.previously_online) {
 		int ret;
 
-		pr_info("Will online and init hotplugged CPU: %d\n",
-			pr->id);
-		pr->flags.need_hotplug_init = 0;
 		ret = __acpi_processor_start(device);
 		WARN(ret, "Failed to start CPU: %d\n", pr->id);
 	} else {
@@ -167,9 +162,6 @@ static int __acpi_processor_start(struct acpi_device *device)
 	if (!pr)
 		return -ENODEV;
 
-	if (pr->flags.need_hotplug_init)
-		return 0;
-
 	result = acpi_cppc_processor_probe(pr);
 	if (result && !IS_ENABLED(CONFIG_ACPI_CPU_FREQ_PSS))
 		dev_dbg(&device->dev, "CPPC data invalid or not present\n");
@@ -185,32 +177,21 @@ static int __acpi_processor_start(struct acpi_device *device)
 
 	status = acpi_install_notify_handler(device->handle, ACPI_DEVICE_NOTIFY,
 					     acpi_processor_notify, device);
-	if (ACPI_SUCCESS(status))
-		return 0;
+	if (!ACPI_SUCCESS(status)) {
+		result = -ENODEV;
+		goto err_thermal_exit;
+	}
+	pr->flags.previously_online = 1;
 
-	result = -ENODEV;
-	acpi_processor_thermal_exit(pr, device);
+	return 0;
 
+err_thermal_exit:
+	acpi_processor_thermal_exit(pr, device);
 err_power_exit:
 	acpi_processor_power_exit(pr);
 	return result;
 }
 
-static int acpi_processor_start(struct device *dev)
-{
-	struct acpi_device *device = ACPI_COMPANION(dev);
-	int ret;
-
-	if (!device)
-		return -ENODEV;
-
-	/* Protect against concurrent CPU hotplug operations */
-	cpu_hotplug_disable();
-	ret = __acpi_processor_start(device);
-	cpu_hotplug_enable();
-	return ret;
-}
-
 static int acpi_processor_stop(struct device *dev)
 {
 	struct acpi_device *device = ACPI_COMPANION(dev);
@@ -279,9 +260,9 @@ static int __init acpi_processor_driver_init(void)
 	if (result < 0)
 		return result;
 
-	result = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
-					   "acpi/cpu-drv:online",
-					   acpi_soft_cpu_online, NULL);
+	result = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN,
+				   "acpi/cpu-drv:online",
+				   acpi_soft_cpu_online, NULL);
 	if (result < 0)
 		goto err;
 	hp_online = result;

include/acpi/processor.h

@@ -217,7 +217,7 @@ struct acpi_processor_flags {
 	u8 has_lpi:1;
 	u8 power_setup_done:1;
 	u8 bm_rld_set:1;
-	u8 need_hotplug_init:1;
+	u8 previously_online:1;
 };
 
 struct acpi_processor {