linux-kernel - [PATCH AUTOSEL 4.14 25/36] i2c: uniphier: issue STOP only for last message or I2C_M

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Message-ID: <20180924144851.164533-25-alexander.levin@microsoft.com>
Date:   Mon, 24 Sep 2018 14:49:07 +0000
From:   Sasha Levin <Alexander.Levin@...rosoft.com>
To:     "stable@...r.kernel.org" <stable@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:     Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Wolfram Sang <wsa@...-dreams.de>,
        Sasha Levin <Alexander.Levin@...rosoft.com>
Subject: [PATCH AUTOSEL 4.14 25/36] i2c: uniphier: issue STOP only for last
 message or I2C_M_STOP

From: Masahiro Yamada <yamada.masahiro@...ionext.com>

[ Upstream commit 38f5d8d8cbb2ffa2b54315118185332329ec891c ]

This driver currently emits a STOP if the next message is not
I2C_MD_RD.  It should not do it because it disturbs the I2C_RDWR
ioctl, where read/write transactions are combined without STOP
between.

Issue STOP only when the message is the last one _or_ flagged with
I2C_M_STOP.

Fixes: dd6fd4a32793 ("i2c: uniphier: add UniPhier FIFO-less I2C driver")
Signed-off-by: Masahiro Yamada <yamada.masahiro@...ionext.com>
Signed-off-by: Wolfram Sang <wsa@...-dreams.de>
Signed-off-by: Sasha Levin <alexander.levin@...rosoft.com>
---
 drivers/i2c/busses/i2c-uniphier.c | 7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

diff --git a/drivers/i2c/busses/i2c-uniphier.c b/drivers/i2c/busses/i2c-uniphier.c
index bb181b088291..454f914ae66d 100644
--- a/drivers/i2c/busses/i2c-uniphier.c
+++ b/drivers/i2c/busses/i2c-uniphier.c
@@ -248,11 +248,8 @@ static int uniphier_i2c_master_xfer(struct i2c_adapter *adap,
 		return ret;
 
 	for (msg = msgs; msg < emsg; msg++) {
-		/* If next message is read, skip the stop condition */
-		bool stop = !(msg + 1 < emsg && msg[1].flags & I2C_M_RD);
-		/* but, force it if I2C_M_STOP is set */
-		if (msg->flags & I2C_M_STOP)
-			stop = true;
+		/* Emit STOP if it is the last message or I2C_M_STOP is set. */
+		bool stop = (msg + 1 == emsg) || (msg->flags & I2C_M_STOP);
 
 		ret = uniphier_i2c_master_xfer_one(adap, msg, stop);
 		if (ret)
-- 
2.17.1