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Subject[PATCH v4 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 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
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