[PATCH linux dev-5.3] i2c: aspeed: Prevent state corruption for IRQ with no status

[Eddie James <eajames@linux.ibm.com>]

On the AST2600, interrupts have been observed with no interrupt status
bits set. This can break the driver state machine, so these interrupts
should be detected and the handler should return IRQ_NONE.

Signed-off-by: Eddie James <eajames@linux.ibm.com>
---
 drivers/i2c/busses/i2c-aspeed.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/drivers/i2c/busses/i2c-aspeed.c b/drivers/i2c/busses/i2c-aspeed.c
index c2a6e5a27314..e19f24c0acb2 100644
--- a/drivers/i2c/busses/i2c-aspeed.c
+++ b/drivers/i2c/busses/i2c-aspeed.c
@@ -603,6 +603,17 @@ static irqreturn_t aspeed_i2c_bus_irq(int irq, void *dev_id)
 
 	spin_lock(&bus->lock);
 	irq_received = readl(bus->base + ASPEED_I2C_INTR_STS_REG);
+
+	/*
+	 * On the AST2600, interrupts have been observed with no interrupt
+	 * status bits set. In this case, the handler should return IRQ_NONE
+	 * immediately to prevent driver state machine corruption.
+	 */
+	if (!irq_received) {
+		spin_unlock(&bus->lock);
+		return IRQ_NONE;
+	}
+
 	/* Ack all interrupts except for Rx done */
 	writel(irq_received & ~ASPEED_I2CD_INTR_RX_DONE,
 	       bus->base + ASPEED_I2C_INTR_STS_REG);
-- 
2.23.0