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Date:   Fri, 13 Mar 2020 17:31:33 +0530
From:   Syed Nayyar Waris <syednwaris@gmail.com>
To:     vilhelm.gray@gmail.com
Cc:     jic23@kernel.org, linux-iio@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: [PATCH v4 2/3] counter: 104-quad-8: Add lock guards - differential
 encoder cable
Message-ID: <20200313120133.GA17830@syed>
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Add lock protection from race conditions in the 104-quad-8 counter
driver for differential encoder cable status changes. There is no IRQ
handling so use spin_lock calls for protection.

Fixes: bbef69e088c3 ("counter: 104-quad-8: Support Differential Encoder Cable Status")

Signed-off-by: Syed Nayyar Waris <syednwaris@gmail.com>
---
Changes in v4:
 - Shift review-comments section so that it is not saved in commit message.
 - Add spin_unlock calls for deadlock avoidance.
 - Few changes related to casting.

 drivers/counter/104-quad-8.c | 18 +++++++++++++++---
 1 file changed, 15 insertions(+), 3 deletions(-)

diff --git a/drivers/counter/104-quad-8.c b/drivers/counter/104-quad-8.c
index 9dab190..c9e227f 100644
--- a/drivers/counter/104-quad-8.c
+++ b/drivers/counter/104-quad-8.c
@@ -1151,18 +1151,26 @@ 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)
+	spin_lock(&priv->lock);
+
+	disabled = !(priv->cable_fault_enable & BIT(channel_id));
+
+	if (disabled) {
+		spin_unlock(&priv->lock);
 		return -EINVAL;
+	}
 
 	/* Logic 0 = cable fault */
 	status = inb(priv->base + QUAD8_DIFF_ENCODER_CABLE_STATUS);
 
+	spin_unlock(&priv->lock);
+
 	/* Mask respective channel and invert logic */
 	fault = !(status & BIT(channel_id));
 
@@ -1194,6 +1202,8 @@ static ssize_t quad8_signal_cable_fault_enable_write(
 	if (ret)
 		return ret;
 
+	spin_lock(&priv->lock);
+
 	if (enable)
 		priv->cable_fault_enable |= BIT(channel_id);
 	else
@@ -1204,6 +1214,8 @@ static ssize_t quad8_signal_cable_fault_enable_write(
 
 	outb(cable_fault_enable, priv->base + QUAD8_DIFF_ENCODER_CABLE_STATUS);
 
+	spin_unlock(&priv->lock);
+
 	return len;
 }
 
-- 
2.7.4