i2c: aspeed: Assert NAK when slave is busy

On I2C_SLAVE_WRITE_REQUESTED event, Slave already ACK'ed on the address
phase. But as the backend driver is busy and unable to process any
request from Master, issue RxCmdLast for Slave to auto send NACK on
next incoming byte.
Signed-off-by: Quan Nguyen <quan@os.amperecomputing.com>
Signed-off-by: Wolfram Sang <wsa@kernel.org>

drivers/i2c/busses/i2c-aspeed.c

@@ -244,6 +244,7 @@ static u32 aspeed_i2c_slave_irq(struct aspeed_i2c_bus *bus, u32 irq_status)
 	u32 command, irq_handled = 0;
 	struct i2c_client *slave = bus->slave;
 	u8 value;
+	int ret;
 
 	if (!slave)
 		return 0;
@@ -311,7 +312,13 @@ static u32 aspeed_i2c_slave_irq(struct aspeed_i2c_bus *bus, u32 irq_status)
 		break;
 	case ASPEED_I2C_SLAVE_WRITE_REQUESTED:
 		bus->slave_state = ASPEED_I2C_SLAVE_WRITE_RECEIVED;
-		i2c_slave_event(slave, I2C_SLAVE_WRITE_REQUESTED, &value);
+		ret = i2c_slave_event(slave, I2C_SLAVE_WRITE_REQUESTED, &value);
+		/*
+		 * Slave ACK's on this address phase already but as the backend driver
+		 * returns an errno, the bus driver should nack the next incoming byte.
+		 */
+		if (ret < 0)
+			writel(ASPEED_I2CD_M_S_RX_CMD_LAST, bus->base + ASPEED_I2C_CMD_REG);
 		break;
 	case ASPEED_I2C_SLAVE_WRITE_RECEIVED:
 		i2c_slave_event(slave, I2C_SLAVE_WRITE_RECEIVED, &value);