ACPI: APEI: EINJ: mark remove callback as __exit

The einj_driver driver is registered using platform_driver_probe(). In
this case it cannot get unbound via sysfs and it's ok to put the remove
callback into an exit section. To prevent the modpost warning about
einj_driver referencing .exit.text, mark the driver struct with
__refdata and explain the situation in a comment.

This is an improvement over commit a24118a8 ("ACPI: APEI: EINJ: mark
remove callback as non-__exit") which recently addressed the same issue,
but picked a less optimal variant.
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/acpi/apei/einj-core.c

@@ -851,7 +851,7 @@ static int __init einj_probe(struct platform_device *pdev)
 	return rc;
 }
 
-static void einj_remove(struct platform_device *pdev)
+static void __exit einj_remove(struct platform_device *pdev)
 {
 	struct apei_exec_context ctx;
 
@@ -873,8 +873,14 @@ static void einj_remove(struct platform_device *pdev)
 }
 
 static struct platform_device *einj_dev;
-static struct platform_driver einj_driver = {
-	.remove_new = einj_remove,
+/*
+ * einj_remove() lives in .exit.text. For drivers registered via
+ * platform_driver_probe() this is ok because they cannot get unbound at
+ * runtime. So mark the driver struct with __refdata to prevent modpost
+ * triggering a section mismatch warning.
+ */
+static struct platform_driver einj_driver __refdata = {
+	.remove_new = __exit_p(einj_remove),
 	.driver = {
 		.name = "acpi-einj",
 	},