ACPI: PAD: xen: Convert to a platform driver

In all cases in which a struct acpi_driver is used for binding a driver
to an ACPI device object, a corresponding platform device is created by
the ACPI core and that device is regarded as a proper representation of
underlying hardware. Accordingly, a struct platform_driver should be
used by driver code to bind to that device. There are multiple reasons
why drivers should not bind directly to ACPI device objects [1].

Overall, it is better to bind drivers to platform devices than to their
ACPI companions, so convert the Xen ACPI processor aggregator device
(PAD) driver to a platform one.

While this is not expected to alter functionality, it changes sysfs
layout and so it will be visible to user space.

Link: https://lore.kernel.org/all/[e-mail]/ [1]
Signed-off-by: Rafael J. Wysocki <[e-mail]>
Link: https://patch.msgid.link/[e-mail]

drivers/xen/xen-acpi-pad.c

···
 #include <linux/kernel.h>
 #include <linux/types.h>
 #include <linux/acpi.h>
+#include <linux/platform_device.h>
 #include <xen/xen.h>
 #include <xen/interface/version.h>
 #include <xen/xen-ops.h>
···
 	}
 }
 
-static int acpi_pad_add(struct acpi_device *device)
+static int acpi_pad_probe(struct platform_device *pdev)
 {
+	struct acpi_device *device = ACPI_COMPANION(&pdev->dev);
 	acpi_status status;
 
 	strcpy(acpi_device_name(device), ACPI_PROCESSOR_AGGREGATOR_DEVICE_NAME);
···
 	return 0;
 }
 
-static void acpi_pad_remove(struct acpi_device *device)
+static void acpi_pad_remove(struct platform_device *pdev)
 {
 	mutex_lock(&xen_cpu_lock);
 	xen_acpi_pad_idle_cpus(0);
 	mutex_unlock(&xen_cpu_lock);
 
-	acpi_remove_notify_handler(device->handle,
+	acpi_remove_notify_handler(ACPI_HANDLE(&pdev->dev),
 		ACPI_DEVICE_NOTIFY, acpi_pad_notify);
 }
 
···
 	{"", 0},
 };
 
-static struct acpi_driver acpi_pad_driver = {
-	.name = "processor_aggregator",
-	.class = ACPI_PROCESSOR_AGGREGATOR_CLASS,
-	.ids = pad_device_ids,
-	.ops = {
-		.add = acpi_pad_add,
-		.remove = acpi_pad_remove,
+static struct platform_driver acpi_pad_driver = {
+	.probe = acpi_pad_probe,
+	.remove = acpi_pad_remove,
+	.driver = {
+		.name = "acpi_processor_aggregator",
+		.acpi_match_table = pad_device_ids,
 	},
 };
 
···
 	if (!xen_running_on_version_or_later(4, 2))
 		return -ENODEV;
 
-	return acpi_bus_register_driver(&acpi_pad_driver);
+	return platform_driver_register(&acpi_pad_driver);
 }
 subsys_initcall(xen_acpi_pad_init);