linux-kernel - [PATCH 019/115] i2c: xiic: must always write 16-bit words to TX

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Message-Id: <1369047116-9378-20-git-send-email-luis.henriques@canonical.com>
Date:	Mon, 20 May 2013 11:50:19 +0100
From:	Luis Henriques <luis.henriques@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	Wolfram Sang <wsa@...-dreams.de>,
	Luis Henriques <luis.henriques@...onical.com>
Subject: [PATCH 019/115] i2c: xiic: must always write 16-bit words to TX_FIFO

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

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

From: "Steven A. Falco" <sfalco@...ris.com>

commit c39e8e4354ce4daf23336de5daa28a3b01f00aa6 upstream.

The TX_FIFO register is 10 bits wide.  The lower 8 bits are the data to be
written, while the upper two bits are flags to indicate stop/start.

The driver apparently attempted to optimize write access, by only writing a
byte in those cases where the stop/start bits are zero.  However, we have
seen cases where the lower byte is duplicated onto the upper byte by the
hardware, which causes inadvertent stop/starts.

This patch changes the write access to the transmit FIFO to always be 16 bits
wide.

Signed off by: Steven A. Falco <sfalco@...ris.com>
Signed-off-by: Wolfram Sang <wsa@...-dreams.de>
Signed-off-by: Luis Henriques <luis.henriques@...onical.com>
---
 drivers/i2c/busses/i2c-xiic.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/drivers/i2c/busses/i2c-xiic.c b/drivers/i2c/busses/i2c-xiic.c
index 641d0e5..15d20de 100644
--- a/drivers/i2c/busses/i2c-xiic.c
+++ b/drivers/i2c/busses/i2c-xiic.c
@@ -312,10 +312,8 @@ static void xiic_fill_tx_fifo(struct xiic_i2c *i2c)
 			/* last message in transfer -> STOP */
 			data |= XIIC_TX_DYN_STOP_MASK;
 			dev_dbg(i2c->adap.dev.parent, "%s TX STOP\n", __func__);
-
-			xiic_setreg16(i2c, XIIC_DTR_REG_OFFSET, data);
-		} else
-			xiic_setreg8(i2c, XIIC_DTR_REG_OFFSET, data);
+		}
+		xiic_setreg16(i2c, XIIC_DTR_REG_OFFSET, data);
 	}
 }
 
-- 
1.8.1.2

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