i2c: designware: Do not enable interrupts shortly in polling mode

I was testing the polling mode txgbe_i2c_dw_xfer_quirk() on a HW where
the i2c-designware has interrupt connected and shared with other device.
I noticed there is a bogus interrupt for each transfer.

Reason for this that both polling mode functions call the
i2c_dw_xfer_init() which enable interrupts then followed by immediate
disable by the same polling mode functions. This is enough to trigger
TX_EMPTY interrupt.

Fix this by introducing a __i2c_dw_write_intr_mask() helper that unmasks
interrupts conditionally and use it in i2c_dw_xfer_init().
Signed-off-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>
Tested-by: Jiawen Wu <jiawenwu@trustnetic.com>
Signed-off-by: Andi Shyti <andi.shyti@kernel.org>

drivers/i2c/busses/i2c-designware-core.h

@@ -352,6 +352,14 @@ static inline void __i2c_dw_disable_nowait(struct dw_i2c_dev *dev)
 	dev->status &= ~STATUS_ACTIVE;
 }
 
+static inline void __i2c_dw_write_intr_mask(struct dw_i2c_dev *dev,
+					    unsigned int intr_mask)
+{
+	unsigned int val = dev->flags & ACCESS_POLLING ? 0 : intr_mask;
+
+	regmap_write(dev->map, DW_IC_INTR_MASK, val);
+}
+
 void __i2c_dw_disable(struct dw_i2c_dev *dev);
 
 extern void i2c_dw_configure_master(struct dw_i2c_dev *dev);

drivers/i2c/busses/i2c-designware-master.c

@@ -250,7 +250,7 @@ static void i2c_dw_xfer_init(struct dw_i2c_dev *dev)
 
 	/* Clear and enable interrupts */
 	regmap_read(dev->map, DW_IC_CLR_INTR, &dummy);
-	regmap_write(dev->map, DW_IC_INTR_MASK, DW_IC_INTR_MASTER_MASK);
+	__i2c_dw_write_intr_mask(dev, DW_IC_INTR_MASTER_MASK);
 }
 
 static int i2c_dw_check_stopbit(struct dw_i2c_dev *dev)
@@ -300,7 +300,6 @@ static int amd_i2c_dw_xfer_quirk(struct i2c_adapter *adap, struct i2c_msg *msgs,
 	dev->msgs = msgs;
 	dev->msgs_num = num_msgs;
 	i2c_dw_xfer_init(dev);
-	regmap_write(dev->map, DW_IC_INTR_MASK, 0);
 
 	/* Initiate messages read/write transaction */
 	for (msg_wrt_idx = 0; msg_wrt_idx < num_msgs; msg_wrt_idx++) {
@@ -384,7 +383,6 @@ static int txgbe_i2c_dw_xfer_quirk(struct i2c_adapter *adap, struct i2c_msg *msg
 	dev->msgs = msgs;
 	dev->msgs_num = num_msgs;
 	i2c_dw_xfer_init(dev);
-	regmap_write(dev->map, DW_IC_INTR_MASK, 0);
 
 	for (msg_idx = 0; msg_idx < num_msgs; msg_idx++) {
 		buf = msgs[msg_idx].buf;