i2c: mediatek: fix potential incorrect use of I2C_MASTER_WRRD

The old IC does not support the I2C_MASTER_WRRD (write-then-read)
function, but the current code’s handling of i2c->auto_restart may
potentially lead to entering the I2C_MASTER_WRRD software flow,
resulting in unexpected bugs.

Instead of repurposing the auto_restart flag, add a separate flag
to signal I2C_MASTER_WRRD operations.

Also fix handling of msgs. If the operation (i2c->op) is
I2C_MASTER_WRRD, then the msgs pointer is incremented by 2.
For all other operations, msgs is simply incremented by 1.

Fixes: b2ed11e ("I2C: mediatek: Add driver for MediaTek MT8173 I2C controller")
Signed-off-by: Leilk.Liu <leilk.liu@mediatek.com>
Suggested-by: Chen-Yu Tsai <wenst@chromium.org>
Reviewed-by: Chen-Yu Tsai <wenst@chromium.org>
Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>

Author: leilkliu

drivers/i2c/busses/i2c-mt65xx.c

@@ -1243,6 +1243,7 @@ static int mtk_i2c_transfer(struct i2c_adapter *adap,
 {
 	int ret;
 	int left_num = num;
+	bool write_then_read_en = false;
 	struct mtk_i2c *i2c = i2c_get_adapdata(adap);
 
 	ret = clk_bulk_enable(I2C_MT65XX_CLK_MAX, i2c->clocks);
@@ -1256,6 +1257,7 @@ static int mtk_i2c_transfer(struct i2c_adapter *adap,
 		if (!(msgs[0].flags & I2C_M_RD) && (msgs[1].flags & I2C_M_RD) &&
 		    msgs[0].addr == msgs[1].addr) {
 			i2c->auto_restart = 0;
+			write_then_read_en = true;
 		}
 	}
 
@@ -1280,20 +1282,21 @@ static int mtk_i2c_transfer(struct i2c_adapter *adap,
 		else
 			i2c->op = I2C_MASTER_WR;
 
-		if (!i2c->auto_restart) {
-			if (num > 1) {
-				/* combined two messages into one transaction */
-				i2c->op = I2C_MASTER_WRRD;
-				left_num--;
-			}
+		if (write_then_read_en) {
+			/* combined two messages into one transaction */
+			i2c->op = I2C_MASTER_WRRD;
+			left_num--;
 		}
 
 		/* always use DMA mode. */
 		ret = mtk_i2c_do_transfer(i2c, msgs, num, left_num);
 		if (ret < 0)
 			goto err_exit;
 
-		msgs++;
+		if (i2c->op == I2C_MASTER_WRRD)
+			msgs += 2;
+		else
+			msgs++;
 	}
 	/* the return value is number of executed messages */
 	ret = num;