[PATCH 2/2] Input: tca8418_keypad - fix race condition in interrupt handler

[Zhian Liang <liangzhan5dev@gmail.com>]

There is a race condition in tca8418_irq_handler() where a new key event
can be lost if it arrives after the FIFO is drained but before the
interrupt status register is cleared.

Fix this by re-reading INT_STAT after draining the FIFO and repeating
the process if K_INT is still asserted. This ensures the FIFO is truly
empty before clearing interrupts.

The FIFO depth is 10 events, so a loop limit of 16 provides sufficient
margin while preventing infinite loops in case of hardware misbehavior.

Signed-off-by: Zhian Liang <liangzhan5dev@gmail.com>
---
 drivers/input/keyboard/tca8418_keypad.c | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/drivers/input/keyboard/tca8418_keypad.c b/drivers/input/keyboard/tca8418_keypad.c
index 9f0aace6bd21..0952370c0636 100644
--- a/drivers/input/keyboard/tca8418_keypad.c
+++ b/drivers/input/keyboard/tca8418_keypad.c
@@ -212,6 +212,7 @@ static irqreturn_t tca8418_irq_handler(int irq, void *dev_id)
 	struct tca8418_keypad *keypad_data = dev_id;
 	u8 reg;
 	int error;
+	int max_loops = 16;
 
 	error = tca8418_read_byte(keypad_data, REG_INT_STAT, &reg);
 	if (error) {
@@ -225,9 +226,19 @@ static irqreturn_t tca8418_irq_handler(int irq, void *dev_id)
 
 	if (reg & INT_STAT_OVR_FLOW_INT)
 		dev_warn(&keypad_data->client->dev, "overflow occurred\n");
+	do {
+		if (reg & INT_STAT_K_INT)
+			tca8418_read_keypad(keypad_data);
+
+		/* Re-read interrupt status to check for new events */
+		error = tca8418_read_byte(keypad_data, REG_INT_STAT, &reg);
+		if (error) {
+			dev_err(&keypad_data->client->dev,
+				"unable to re-read REG_INT_STAT\n");
+			return IRQ_HANDLED;
+		}
 
-	if (reg & INT_STAT_K_INT)
-		tca8418_read_keypad(keypad_data);
+	} while ((reg & INT_STAT_K_INT) && --max_loops);
 
 	/* Clear all interrupts, even IRQs we didn't check (GPI, CAD, LCK) */
 	reg = 0xff;
-- 
2.34.1