[PATCH v3 3/8] rtc: abx80x: properly handle shared IRQs

The abx80x RTC driver registers its interrupt handler with IRQF_SHARED,
but the handler always returned IRQ_HANDLED and cleared the status
register even when no interrupt source from the RTC was active.

This could cause the driver to claim interrupts belonging to other
devices sharing the same IRQ line and could also clear unrelated status
bits in the RTC status register.

Only handle the interrupt when the alarm or watchdog flags are set, and
clear only those interrupt status bits that were handled. Return
IRQ_NONE when the interrupt was not generated by the RTC.

Fixes: 718a820a303c ("rtc: abx80x: add alarm support")
Signed-off-by: Antoni Pokusinski <[email protected]>
---
 drivers/rtc/rtc-abx80x.c | 17 ++++++++++++-----
 1 file changed, 12 insertions(+), 5 deletions(-)

diff --git a/drivers/rtc/rtc-abx80x.c b/drivers/rtc/rtc-abx80x.c
index 8d791b9ec7d2..b84fce0ef294 100644
--- a/drivers/rtc/rtc-abx80x.c
+++ b/drivers/rtc/rtc-abx80x.c
@@ -266,27 +266,34 @@ static irqreturn_t abx80x_handle_irq(int irq, void *dev_id)
 	struct i2c_client *client = dev_id;
 	struct abx80x_priv *priv = i2c_get_clientdata(client);
 	struct rtc_device *rtc = priv->rtc;
+	irqreturn_t handled = IRQ_NONE;
 	int status;
 
 	guard(mutex)(&priv->lock);
 
 	status = i2c_smbus_read_byte_data(client, ABX8XX_REG_STATUS);
 	if (status < 0)
-		return IRQ_NONE;
+		return handled;
 
-	if (status & ABX8XX_STATUS_AF)
+	if (status & ABX8XX_STATUS_AF) {
 		rtc_update_irq(rtc, 1, RTC_AF | RTC_IRQF);
+		handled = IRQ_HANDLED;
+	}
 
 	/*
 	 * It is unclear if we'll get an interrupt before the external
 	 * reset kicks in.
 	 */
-	if (status & ABX8XX_STATUS_WDT)
+	if (status & ABX8XX_STATUS_WDT) {
 		dev_alert(&client->dev, "watchdog timeout interrupt.\n");
+		handled = IRQ_HANDLED;
+	}
 
-	i2c_smbus_write_byte_data(client, ABX8XX_REG_STATUS, 0);
+	if (handled == IRQ_HANDLED)
+		i2c_smbus_write_byte_data(client, ABX8XX_REG_STATUS,
+					  status & ~(ABX8XX_STATUS_AF | ABX8XX_STATUS_WDT));
 
-	return IRQ_HANDLED;
+	return handled;
 }
 
 static int abx80x_read_alarm(struct device *dev, struct rtc_wkalrm *t)
-- 
2.55.0