linux-kernel - [PATCH v3 2/3] counter: 104-quad-8: Add lock guards

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Date:   Thu, 12 Mar 2020 16:55:17 +0530
From:   Syed Nayyar Waris <syednwaris@...il.com>
To:     vilhelm.gray@...il.com
Cc:     jic23@...nel.org, linux-iio@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH v3 2/3] counter: 104-quad-8: Add lock guards - differential
 encoder cable

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 spin_lock calls are used for protection.

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

Signed-off-by: Syed Nayyar Waris <syednwaris@...il.com>

Split the patch from generic driver interface and clock prescaler
related code changes. Also, include more code statements for protection
using spin_lock calls and remove protection from few code statements as
they are unnecessary.
---
 drivers/counter/104-quad-8.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/drivers/counter/104-quad-8.c b/drivers/counter/104-quad-8.c
index 9dab190..1ce9660 100644
--- a/drivers/counter/104-quad-8.c
+++ b/drivers/counter/104-quad-8.c
@@ -1153,16 +1153,22 @@ static ssize_t quad8_signal_cable_fault_read(struct counter_device *counter,
 {
 	const 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;
 
+	spin_lock(&((struct quad8_iio *)priv)->lock);
+
+	disabled = !(priv->cable_fault_enable & BIT(channel_id));
+
 	if (disabled)
 		return -EINVAL;
 
 	/* Logic 0 = cable fault */
 	status = inb(priv->base + QUAD8_DIFF_ENCODER_CABLE_STATUS);
 
+	spin_unlock(&((struct quad8_iio *)priv)->lock);
+
 	/* Mask respective channel and invert logic */
 	fault = !(status & BIT(channel_id));
 
@@ -1194,6 +1200,8 @@ 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 +1212,8 @@ 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