i2c: designware: Manually set RESTART bit between messages

If both IC_EMPTYFIFO_HOLD_MASTER_EN and IC_RESTART_EN are set to 1, the
Designware I2C controller doesn't generate RESTART unless user specifically
requests it by setting RESTART bit in IC_DATA_CMD register.

Since IC_EMPTYFIFO_HOLD_MASTER_EN setting can't be detected from hardware
register, we must always manually set the restart bit between messages.
Signed-off-by: Chew, Chiau Ee <chiau.ee.chew@intel.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>

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

@@ -416,6 +416,7 @@ i2c_dw_xfer_msg(struct dw_i2c_dev *dev)
 	u32 addr = msgs[dev->msg_write_idx].addr;
 	u32 buf_len = dev->tx_buf_len;
 	u8 *buf = dev->tx_buf;
+	bool need_restart = false;
 
 	intr_mask = DW_IC_INTR_DEFAULT_MASK;
 
@@ -443,6 +444,14 @@ i2c_dw_xfer_msg(struct dw_i2c_dev *dev)
 			/* new i2c_msg */
 			buf = msgs[dev->msg_write_idx].buf;
 			buf_len = msgs[dev->msg_write_idx].len;
+
+			/* If both IC_EMPTYFIFO_HOLD_MASTER_EN and
+			 * IC_RESTART_EN are set, we must manually
+			 * set restart bit between messages.
+			 */
+			if ((dev->master_cfg & DW_IC_CON_RESTART_EN) &&
+					(dev->msg_write_idx > 0))
+				need_restart = true;
 		}
 
 		tx_limit = dev->tx_fifo_depth - dw_readl(dev, DW_IC_TXFLR);
@@ -461,6 +470,11 @@ i2c_dw_xfer_msg(struct dw_i2c_dev *dev)
 			    buf_len == 1)
 				cmd |= BIT(9);
 
+			if (need_restart) {
+				cmd |= BIT(10);
+				need_restart = false;
+			}
+
 			if (msgs[dev->msg_write_idx].flags & I2C_M_RD) {
 
 				/* avoid rx buffer overrun */