linux-kernel - [PATCH] i2c: mediatek: fix potential incorrect use of I2C_MASTER

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Message-ID: <20250816075434.31780-1-leilk.liu@mediatek.com>
Date: Sat, 16 Aug 2025 15:53:54 +0800
From: Leilk Liu <leilk.liu@...iatek.com>
To: Andi Shyti <andi.shyti@...nel.org>, Matthias Brugger
	<matthias.bgg@...il.com>, AngeloGioacchino Del Regno
	<angelogioacchino.delregno@...labora.com>
CC: Qii Wang <qii.wang@...iatek.com>, Wolfram Sang <wsa@...nel.org>, Liguo
 Zhang <liguo.zhang@...iatek.com>, <linux-i2c@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <linux-arm-kernel@...ts.infradead.org>,
	<linux-mediatek@...ts.infradead.org>,
	<Project_Global_Chrome_Upstream_Group@...iatek.com>, Leilk.Liu
	<leilk.liu@...iatek.com>
Subject: [PATCH] i2c: mediatek: fix potential incorrect use of I2C_MASTER_WRRD

From: "Leilk.Liu" <leilk.liu@...iatek.com>

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: 173b77e8d8fe ("i2c: mediatek: add i2c first write then read optimization")

Signed-off-by: Leilk.Liu <leilk.liu@...iatek.com>
---
 drivers/i2c/busses/i2c-mt65xx.c | 17 ++++++++++-------
 1 file changed, 10 insertions(+), 7 deletions(-)

diff --git a/drivers/i2c/busses/i2c-mt65xx.c b/drivers/i2c/busses/i2c-mt65xx.c
index ab456c3717db..dee40704825c 100644
--- a/drivers/i2c/busses/i2c-mt65xx.c
+++ b/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;
 		}
 	}
 
@@ -1280,12 +1282,10 @@ 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. */
@@ -1293,7 +1293,10 @@ static int mtk_i2c_transfer(struct i2c_adapter *adap,
 		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;
-- 
2.46.0