hwmon: (vt1211) 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: 2219cd8 ("hwmon/vt1211: Add probing of alternate config index port")
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

drivers/hwmon/vt1211.c

@@ -226,15 +226,21 @@ static inline void superio_select(int sio_cip, int ldn)
 	outb(ldn, sio_cip + 1);
 }
 
-static inline void superio_enter(int sio_cip)
+static inline int superio_enter(int sio_cip)
 {
+	if (!request_muxed_region(sio_cip, 2, DRVNAME))
+		return -EBUSY;
+
 	outb(0x87, sio_cip);
 	outb(0x87, sio_cip);
+
+	return 0;
 }
 
 static inline void superio_exit(int sio_cip)
 {
 	outb(0xaa, sio_cip);
+	release_region(sio_cip, 2);
 }
 
 /* ---------------------------------------------------------------------
@@ -1282,11 +1288,14 @@ static int __init vt1211_device_add(unsigned short address)
 
 static int __init vt1211_find(int sio_cip, unsigned short *address)
 {
-	int err = -ENODEV;
+	int err;
 	int devid;
 
-	superio_enter(sio_cip);
+	err = superio_enter(sio_cip);
+	if (err)
+		return err;
 
+	err = -ENODEV;
 	devid = force_id ? force_id : superio_inb(sio_cip, SIO_VT1211_DEVID);
 	if (devid != SIO_VT1211_ID)
 		goto EXIT;