hwmon: (f71805f) Use request_muxed_region for Super-IO accesses

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

Unable to handle kernel paging request at virtual address ffffffbffee0002e
pgd = ffffffc1d68d4000
[ffffffbffee0002e] *pgd=0000000000000000, *pud=0000000000000000
Internal error: Oops: 94000046 [#1] PREEMPT SMP
Modules linked in: f71805f(+) hwmon
CPU: 3 PID: 1659 Comm: insmod Not tainted 4.5.0+ #88
Hardware name: linux,dummy-virt (DT)
task: ffffffc1f6665400 ti: ffffffc1d6418000 task.ti: ffffffc1d6418000
PC is at f71805f_find+0x6c/0x358 [f71805f]

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: e53004e2 ("hwmon: New f71805f driver")
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/f71805f.c

@@ -96,17 +96,23 @@ superio_select(int base, int ld)
 	outb(ld, base + 1);
 }
 
-static inline void
+static inline int
 superio_enter(int base)
 {
+	if (!request_muxed_region(base, 2, DRVNAME))
+		return -EBUSY;
+
 	outb(0x87, base);
 	outb(0x87, base);
+
+	return 0;
 }
 
 static inline void
 superio_exit(int base)
 {
 	outb(0xaa, base);
+	release_region(base, 2);
 }
 
 /*
@@ -1561,7 +1567,7 @@ static int __init f71805f_device_add(unsigned short address,
 static int __init f71805f_find(int sioaddr, unsigned short *address,
 			       struct f71805f_sio_data *sio_data)
 {
-	int err = -ENODEV;
+	int err;
 	u16 devid;
 
 	static const char * const names[] = {
@@ -1569,8 +1575,11 @@ static int __init f71805f_find(int sioaddr, unsigned short *address,
 		"F71872F/FG or F71806F/FG",
 	};
 
-	superio_enter(sioaddr);
+	err = superio_enter(sioaddr);
+	if (err)
+		return err;
 
+	err = -ENODEV;
 	devid = superio_inw(sioaddr, SIO_REG_MANID);
 	if (devid != SIO_FINTEK_ID)
 		goto exit;