EINJ: Migrate to a platform driver

Change the EINJ module to install a platform device/driver on module
init and move the module init() and exit() functions to driver probe and
remove. This change allows the EINJ module to load regardless of whether
setting up EINJ succeeds, which allows dependent modules to still load
(i.e. the CXL core).

Since EINJ may no longer be initialized when the module loads, any
functions that are called from dependent/external modules should
safegaurd against the case EINJ didn't load.

Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Ben Cheatham <Benjamin.Cheatham@amd.com>
Link: https://lore.kernel.org/r/20240311142508.31717-2-Benjamin.Cheatham@amd.com
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

drivers/acpi/apei/einj.c

@@ -21,6 +21,7 @@
 #include <linux/nmi.h>
 #include <linux/delay.h>
 #include <linux/mm.h>
+#include <linux/platform_device.h>
 #include <asm/unaligned.h>
 
 #include "apei-internal.h"
@@ -137,6 +138,11 @@ static struct apei_exec_ins_type einj_ins_type[] = {
  */
 static DEFINE_MUTEX(einj_mutex);
 
+/*
+ * Exported APIs use this flag to exit early if einj_probe() failed.
+ */
+static bool einj_initialized __ro_after_init;
+
 static void *einj_param;
 
 static void einj_exec_ctx_init(struct apei_exec_context *ctx)
@@ -703,21 +709,21 @@ static int einj_check_table(struct acpi_table_einj *einj_tab)
 	return 0;
 }
 
-static int __init einj_init(void)
+static int __init einj_probe(struct platform_device *pdev)
 {
 	int rc;
 	acpi_status status;
 	struct apei_exec_context ctx;
 
 	if (acpi_disabled) {
-		pr_info("ACPI disabled.\n");
+		pr_debug("ACPI disabled.\n");
 		return -ENODEV;
 	}
 
 	status = acpi_get_table(ACPI_SIG_EINJ, 0,
 				(struct acpi_table_header **)&einj_tab);
 	if (status == AE_NOT_FOUND) {
-		pr_warn("EINJ table not found.\n");
+		pr_debug("EINJ table not found.\n");
 		return -ENODEV;
 	} else if (ACPI_FAILURE(status)) {
 		pr_err("Failed to get EINJ table: %s\n",
@@ -805,7 +811,7 @@ static int __init einj_init(void)
 	return rc;
 }
 
-static void __exit einj_exit(void)
+static void __exit einj_remove(struct platform_device *pdev)
 {
 	struct apei_exec_context ctx;
 
@@ -826,6 +832,40 @@ static void __exit einj_exit(void)
 	acpi_put_table((struct acpi_table_header *)einj_tab);
 }
 
+static struct platform_device *einj_dev;
+static struct platform_driver einj_driver = {
+	.remove_new = einj_remove,
+	.driver = {
+		.name = "acpi-einj",
+	},
+};
+
+static int __init einj_init(void)
+{
+	struct platform_device_info einj_dev_info = {
+		.name = "acpi-einj",
+		.id = -1,
+	};
+	int rc;
+
+	einj_dev = platform_device_register_full(&einj_dev_info);
+	if (IS_ERR(einj_dev))
+		return PTR_ERR(einj_dev);
+
+	rc = platform_driver_probe(&einj_driver, einj_probe);
+	einj_initialized = rc == 0;
+
+	return 0;
+}
+
+static void __exit einj_exit(void)
+{
+	if (einj_initialized)
+		platform_driver_unregister(&einj_driver);
+
+	platform_device_del(einj_dev);
+}
+
 module_init(einj_init);
 module_exit(einj_exit);