ACPI: ibm-acpi: allow module to load when acpi notifiers can't be set (v2)

This patch allows for ibm-acpi to coexist (with diminished functionality) with
other drivers like ACPI_BAY.  ibm-acpi will simply disable the functions it is
not able to register ACPI notifiers for.
Signed-off-by: Henrique de Moraes Holschuh <hmh@hmh.eng.br>
Cc: Chris Wedgwood <cw@f00f.org>
Cc: Kristen Carlson Accardi <kristen.c.accardi@intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>

drivers/acpi/ibm_acpi.c

@@ -2507,7 +2507,7 @@ static int __init setup_notify(struct ibm_struct *ibm)
 	ret = acpi_bus_get_device(*ibm->handle, &ibm->device);
 	if (ret < 0) {
 		printk(IBM_ERR "%s device not present\n", ibm->name);
-		return 0;
+		return -ENODEV;
 	}
 
 	acpi_driver_data(ibm->device) = ibm;
@@ -2516,8 +2516,13 @@ static int __init setup_notify(struct ibm_struct *ibm)
 	status = acpi_install_notify_handler(*ibm->handle, ibm->type,
 					     dispatch_notify, ibm);
 	if (ACPI_FAILURE(status)) {
-		printk(IBM_ERR "acpi_install_notify_handler(%s) failed: %d\n",
-		       ibm->name, status);
+		if (status == AE_ALREADY_EXISTS) {
+			printk(IBM_NOTICE "another device driver is already handling %s events\n",
+				ibm->name);
+		} else {
+			printk(IBM_ERR "acpi_install_notify_handler(%s) failed: %d\n",
+				ibm->name, status);
+		}
 		return -ENODEV;
 	}
 	ibm->notify_installed = 1;
@@ -2553,6 +2558,8 @@ static int __init register_driver(struct ibm_struct *ibm)
 	return ret;
 }
 
+static void ibm_exit(struct ibm_struct *ibm);
+
 static int __init ibm_init(struct ibm_struct *ibm)
 {
 	int ret;
@@ -2594,6 +2601,12 @@ static int __init ibm_init(struct ibm_struct *ibm)
 
 	if (ibm->notify) {
 		ret = setup_notify(ibm);
+		if (ret == -ENODEV) {
+			printk(IBM_NOTICE "disabling subdriver %s\n",
+				ibm->name);
+			ibm_exit(ibm);
+			return 0;
+		}
 		if (ret < 0)
 			return ret;
 	}