i2c: aspeed: Avoid i2c interrupt status clear race condition.

In AST2600 there have a slow peripheral bus between CPU and i2c
controller. Therefore GIC i2c interrupt status clear have delay timing,
when CPU issue write clear i2c controller interrupt status. To avoid
this issue, the driver need have read after write clear at i2c ISR.

Fixes: f327c686 ("i2c: aspeed: added driver for Aspeed I2C")
Signed-off-by: Nryan_chen <ryan_chen@aspeedtech.com>
Acked-by: NBenjamin Herrenschmidt <benh@kernel.crashing.org>
[wsa: added Fixes tag]
Signed-off-by: NWolfram Sang <wsa@the-dreams.de>

drivers/i2c/busses/i2c-aspeed.c

@@ -603,6 +603,7 @@ static irqreturn_t aspeed_i2c_bus_irq(int irq, void *dev_id)
 	/* Ack all interrupts except for Rx done */
 	writel(irq_received & ~ASPEED_I2CD_INTR_RX_DONE,
 	       bus->base + ASPEED_I2C_INTR_STS_REG);
+	readl(bus->base + ASPEED_I2C_INTR_STS_REG);
 	irq_remaining = irq_received;
 
 #if IS_ENABLED(CONFIG_I2C_SLAVE)
@@ -645,9 +646,11 @@ static irqreturn_t aspeed_i2c_bus_irq(int irq, void *dev_id)
 			irq_received, irq_handled);
 
 	/* Ack Rx done */
-	if (irq_received & ASPEED_I2CD_INTR_RX_DONE)
+	if (irq_received & ASPEED_I2CD_INTR_RX_DONE) {
 		writel(ASPEED_I2CD_INTR_RX_DONE,
 		       bus->base + ASPEED_I2C_INTR_STS_REG);
+		readl(bus->base + ASPEED_I2C_INTR_STS_REG);
+	}
 	spin_unlock(&bus->lock);
 	return irq_remaining ? IRQ_NONE : IRQ_HANDLED;
 }