hwmon: (smsc47m1) Use request_muxed_region for Super-IO accesses

Super-IO accesses may fail on a system with no or unmapped LPC bus.

Also, other drivers may attempt to access the LPC bus at the same time,
resulting in undefined behavior.

Use request_muxed_region() to ensure that IO access on the requested
address space is supported, and to ensure that access by multiple drivers
is synchronized.

Fixes: 8d5d45fb14 ("I2C: Move hwmon drivers (2/3)")
Reported-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Reported-by: John Garry <john.garry@huawei.com>
Cc: John Garry <john.garry@huawei.com>
Acked-by: John Garry <john.garry@huawei.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

drivers/hwmon/smsc47m1.c

@@ -73,16 +73,21 @@ superio_inb(int reg)
 /* logical device for fans is 0x0A */
 #define superio_select() superio_outb(0x07, 0x0A)
 
-static inline void
+static inline int
 superio_enter(void)
 {
+	if (!request_muxed_region(REG, 2, DRVNAME))
+		return -EBUSY;
+
 	outb(0x55, REG);
+	return 0;
 }
 
 static inline void
 superio_exit(void)
 {
 	outb(0xAA, REG);
+	release_region(REG, 2);
 }
 
 #define SUPERIO_REG_ACT		0x30
@@ -535,8 +540,12 @@ static int __init smsc47m1_find(struct smsc47m1_sio_data *sio_data)
 {
 	u8 val;
 	unsigned short addr;
+	int err;
+
+	err = superio_enter();
+	if (err)
+		return err;
 
-	superio_enter();
 	val = force_id ? force_id : superio_inb(SUPERIO_REG_DEVID);
 
 	/*
@@ -612,13 +621,14 @@ static int __init smsc47m1_find(struct smsc47m1_sio_data *sio_data)
 static void smsc47m1_restore(const struct smsc47m1_sio_data *sio_data)
 {
 	if ((sio_data->activate & 0x01) == 0) {
-		superio_enter();
+		if (!superio_enter()) {
-		superio_select();
+			superio_select();
-
+			pr_info("Disabling device\n");
-		pr_info("Disabling device\n");
+			superio_outb(SUPERIO_REG_ACT, sio_data->activate);
-		superio_outb(SUPERIO_REG_ACT, sio_data->activate);
+			superio_exit();
-
+		} else {
-		superio_exit();
+			pr_warn("Failed to disable device\n");
+		}
 	}
 }