counter: 104-quad-8: Add lock guards - differential encoder

Add lock protection from race conditions to 104-quad-8 counter driver
for differential encoder status code changes. Mutex lock calls used for
protection.

Signed-off-by: Syed Nayyar Waris <syednwaris@gmail.com>
Fixes: 954ab5c ("counter: 104-quad-8: Support Differential Encoder Cable Status")
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/counter/104-quad-8.c

@@ -1274,18 +1274,26 @@ static ssize_t quad8_signal_cable_fault_read(struct counter_device *counter,
 					     struct counter_signal *signal,
 					     void *private, char *buf)
 {
-	const struct quad8_iio *const priv = counter->priv;
+	struct quad8_iio *const priv = counter->priv;
 	const size_t channel_id = signal->id / 2;
-	const bool disabled = !(priv->cable_fault_enable & BIT(channel_id));
+	bool disabled;
 	unsigned int status;
 	unsigned int fault;
 
-	if (disabled)
+	mutex_lock(&priv->lock);
+
+	disabled = !(priv->cable_fault_enable & BIT(channel_id));
+
+	if (disabled) {
+		mutex_unlock(&priv->lock);
 		return -EINVAL;
+	}
 
 	/* Logic 0 = cable fault */
 	status = inb(priv->base + QUAD8_DIFF_ENCODER_CABLE_STATUS);
 
+	mutex_unlock(&priv->lock);
+
 	/* Mask respective channel and invert logic */
 	fault = !(status & BIT(channel_id));
 
@@ -1317,6 +1325,8 @@ static ssize_t quad8_signal_cable_fault_enable_write(
 	if (ret)
 		return ret;
 
+	mutex_lock(&priv->lock);
+
 	if (enable)
 		priv->cable_fault_enable |= BIT(channel_id);
 	else
@@ -1327,6 +1337,8 @@ static ssize_t quad8_signal_cable_fault_enable_write(
 
 	outb(cable_fault_enable, priv->base + QUAD8_DIFF_ENCODER_CABLE_STATUS);
 
+	mutex_unlock(&priv->lock);
+
 	return len;
 }