watchdog: cpwd: use generic compat_ptr_ioctl

The cpwd_compat_ioctl() contains a bogus mutex that dates
back to a leftover BKL instance.

Simplify the implementation by using the new compat_ptr_ioctl()
helper function that will do the right thing for all calls
here.

Note that WIOCSTART/WIOCSTOP don't take any arguments, so
the compat_ptr() conversion is not needed here, but it also
doesn't hurt.
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20190814204259.120942-6-arnd@arndb.deSigned-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>

drivers/watchdog/cpwd.c

@@ -473,29 +473,6 @@ static long cpwd_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 	return 0;
 }
 
-static long cpwd_compat_ioctl(struct file *file, unsigned int cmd,
-			      unsigned long arg)
-{
-	int rval = -ENOIOCTLCMD;
-
-	switch (cmd) {
-	/* solaris ioctls are specific to this driver */
-	case WIOCSTART:
-	case WIOCSTOP:
-	case WIOCGSTAT:
-		mutex_lock(&cpwd_mutex);
-		rval = cpwd_ioctl(file, cmd, arg);
-		mutex_unlock(&cpwd_mutex);
-		break;
-
-	/* everything else is handled by the generic compat layer */
-	default:
-		break;
-	}
-
-	return rval;
-}
-
 static ssize_t cpwd_write(struct file *file, const char __user *buf,
 			  size_t count, loff_t *ppos)
 {
@@ -520,7 +497,7 @@ static ssize_t cpwd_read(struct file *file, char __user *buffer,
 static const struct file_operations cpwd_fops = {
 	.owner =		THIS_MODULE,
 	.unlocked_ioctl =	cpwd_ioctl,
-	.compat_ioctl =		cpwd_compat_ioctl,
+	.compat_ioctl =		compat_ptr_ioctl,
 	.open =			cpwd_open,
 	.write =		cpwd_write,
 	.read =			cpwd_read,