[PATCH 3.16 031/132] hwmon: (smsc47m1) Use request_muxed_region for Super-IO accesses

[Ben Hutchings]

3.16.74-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Guenter Roeck <linux@xxxxxxxxxxxx>

commit d6410408ad2a798c4cc685252c1baa713be0ad69 upstream.

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: 8d5d45fb1468 ("I2C: Move hwmon drivers (2/3)")
Reported-by: Kefeng Wang <wangkefeng.wang@xxxxxxxxxx>
Reported-by: John Garry <john.garry@xxxxxxxxxx>
Cc: John Garry <john.garry@xxxxxxxxxx>
Acked-by: John Garry <john.garry@xxxxxxxxxx>
Signed-off-by: Guenter Roeck <linux@xxxxxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 drivers/hwmon/smsc47m1.c | 28 +++++++++++++++++++---------
 1 file changed, 19 insertions(+), 9 deletions(-)

--- a/drivers/hwmon/smsc47m1.c
+++ b/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
@@ -495,8 +500,12 @@ static int __init smsc47m1_find(struct s
 {
 	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);
 
 	/*
@@ -572,13 +581,14 @@ static int __init smsc47m1_find(struct s
 static void smsc47m1_restore(const struct smsc47m1_sio_data *sio_data)
 {
 	if ((sio_data->activate & 0x01) == 0) {
-		superio_enter();
-		superio_select();
-
-		pr_info("Disabling device\n");
-		superio_outb(SUPERIO_REG_ACT, sio_data->activate);
-
-		superio_exit();
+		if (!superio_enter()) {
+			superio_select();
+			pr_info("Disabling device\n");
+			superio_outb(SUPERIO_REG_ACT, sio_data->activate);
+			superio_exit();
+		} else {
+			pr_warn("Failed to disable device\n");
+		}
 	}
 }