[PATCH v10 3/3] i2c: aspeed: Assert NAK when slave is busy

[Quan Nguyen]

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 at os.amperecomputing.com>
---
v10:
  + Issuing RxCmdLast command for all errnos     [Wolfram]

v9:
  + Update commit message and add comment to explain
    the effect of issuing RxCmdLast when Slave busy [Quan]

v7 -> v8:
  + None

v6:
  + New introduced in v6                            [Quan]
---
 drivers/i2c/busses/i2c-aspeed.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/drivers/i2c/busses/i2c-aspeed.c b/drivers/i2c/busses/i2c-aspeed.c
index 185dedfebbac..c64c381b69b7 100644
--- a/drivers/i2c/busses/i2c-aspeed.c
+++ b/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);
-- 
2.35.1