[PATCH v4 3/3] counter: 104-quad-8: Add lock guards - filter clock prescaler

[Syed Nayyar Waris <syednwaris@gmail.com>]

Add lock protection from race conditions in the 104-quad-8 counter
driver for filter clock prescaler related changes. There is no IRQ
handling so used spin_lock calls for protection.

Fixes: 9b74dddf79be ("counter: 104-quad-8: Support Filter Clock Prescaler")

Signed-off-by: Syed Nayyar Waris <syednwaris@gmail.com>
Signed-off-by: William Breathitt Gray <vilhelm.gray@gmail.com>
---
Changes in v4:
 - Shift review-comments section so that it is not in commit message.

 drivers/counter/104-quad-8.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/counter/104-quad-8.c b/drivers/counter/104-quad-8.c
index 9dab190..58615e4 100644
--- a/drivers/counter/104-quad-8.c
+++ b/drivers/counter/104-quad-8.c
@@ -1230,6 +1230,8 @@ static ssize_t quad8_signal_fck_prescaler_write(struct counter_device *counter,
 	if (ret)
 		return ret;
 
+	spin_lock(&priv->lock);
+
 	priv->fck_prescaler[channel_id] = prescaler;
 
 	/* Reset Byte Pointer */
@@ -1240,6 +1242,8 @@ static ssize_t quad8_signal_fck_prescaler_write(struct counter_device *counter,
 	outb(QUAD8_CTR_RLD | QUAD8_RLD_RESET_BP | QUAD8_RLD_PRESET_PSC,
 	     base_offset + 1);
 
+	spin_unlock(&priv->lock);
+
 	return len;
 }
 
-- 
2.7.4