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: 954ab5cc5f3e ("counter: 104-quad-8: Support Differential Encoder Cable Status")
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

diff --git a/drivers/counter/104-quad-8.c b/drivers/counter/104-quad-8.c
index aa13708..9364dc1 100644 (file)
--- a/drivers/counter/104-quad-8.c
+++ b/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;
 }