linux-kernel - [PATCH 4.17 47/67] i2c: recovery: if possible send STOP with recovery pulses

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Date:   Mon, 16 Jul 2018 09:35:16 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        Wolfram Sang <wsa+renesas@...g-engineering.com>,
        Peter Rosin <peda@...ntia.se>,
        Wolfram Sang <wsa@...-dreams.de>, stable@...nel.org
Subject: [PATCH 4.17 47/67] i2c: recovery: if possible send STOP with recovery pulses

4.17-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Wolfram Sang <wsa+renesas@...g-engineering.com>

commit abe41184abac487264a4904bfcff2d5500dccce6 upstream.

I2C clients may misunderstand recovery pulses if they can't read SDA to
bail out early. In the worst case, as a write operation. To avoid that
and if we can write SDA, try to send STOP to avoid the
misinterpretation.

Signed-off-by: Wolfram Sang <wsa+renesas@...g-engineering.com>
Reviewed-by: Peter Rosin <peda@...ntia.se>
Signed-off-by: Wolfram Sang <wsa@...-dreams.de>
Cc: stable@...nel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/i2c/i2c-core-base.c |   11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

--- a/drivers/i2c/i2c-core-base.c
+++ b/drivers/i2c/i2c-core-base.c
@@ -198,7 +198,16 @@ int i2c_generic_scl_recovery(struct i2c_
 
 		val = !val;
 		bri->set_scl(adap, val);
-		ndelay(RECOVERY_NDELAY);
+
+		/*
+		 * If we can set SDA, we will always create STOP here to ensure
+		 * the additional pulses will do no harm. This is achieved by
+		 * letting SDA follow SCL half a cycle later.
+		 */
+		ndelay(RECOVERY_NDELAY / 2);
+		if (bri->set_sda)
+			bri->set_sda(adap, val);
+		ndelay(RECOVERY_NDELAY / 2);
 	}
 
 	/* check if recovery actually succeeded */