linux-kernel - [065/289] viafb: fix i2c

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Message-Id: <20101208005727.836865092@clark.site>
Date:	Tue, 07 Dec 2010 16:57:22 -0800
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...nel.org
Cc:	stable-review@...nel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	Florian Tobias Schandinat <FlorianSchandinat@....de>,
	Jonathan Corbet <corbet@....net>,
	Joseph Chan <JosephChan@....com.tw>
Subject: [065/289] viafb: fix i2c_transfer error handling

2.6.36-stable review patch.  If anyone has any objections, please let us know.

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

From: Florian Tobias Schandinat <FlorianSchandinat@....de>

commit 85c5702ac046b14713f776d59768252d8ed8018f upstream.

i2c_transfer returns negative errno on error and number of messages
processed on success. Just returning this value would give a poor
interface as it is not obvious that you must compare with 2 after reading
1 or n bytes and with 1 after writing 1 byte to determine if it was
successful. To avoid this error prone interface convert the error code
of a successful read/write to zero and all other non-negative values to
an negative error code.
This fixes a regression introduced by
	via: Rationalize vt1636 detection
which resulted in no longer detecting a VT1636 chip and therefore has
broken the output in configurations which contain this chip.

Signed-off-by: Florian Tobias Schandinat <FlorianSchandinat@....de>
Acked-by: Jonathan Corbet <corbet@....net>
Cc: Joseph Chan <JosephChan@....com.tw>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

---
 drivers/video/via/via_i2c.c |   27 ++++++++++++++++++++++++---
 1 file changed, 24 insertions(+), 3 deletions(-)

--- a/drivers/video/via/via_i2c.c
+++ b/drivers/video/via/via_i2c.c
@@ -114,6 +114,7 @@ static void via_i2c_setsda(void *data, i
 
 int viafb_i2c_readbyte(u8 adap, u8 slave_addr, u8 index, u8 *pdata)
 {
+	int ret;
 	u8 mm1[] = {0x00};
 	struct i2c_msg msgs[2];
 
@@ -126,11 +127,18 @@ int viafb_i2c_readbyte(u8 adap, u8 slave
 	mm1[0] = index;
 	msgs[0].len = 1; msgs[1].len = 1;
 	msgs[0].buf = mm1; msgs[1].buf = pdata;
-	return i2c_transfer(&via_i2c_par[adap].adapter, msgs, 2);
+	ret = i2c_transfer(&via_i2c_par[adap].adapter, msgs, 2);
+	if (ret == 2)
+		ret = 0;
+	else if (ret >= 0)
+		ret = -EIO;
+
+	return ret;
 }
 
 int viafb_i2c_writebyte(u8 adap, u8 slave_addr, u8 index, u8 data)
 {
+	int ret;
 	u8 msg[2] = { index, data };
 	struct i2c_msg msgs;
 
@@ -140,11 +148,18 @@ int viafb_i2c_writebyte(u8 adap, u8 slav
 	msgs.addr = slave_addr / 2;
 	msgs.len = 2;
 	msgs.buf = msg;
-	return i2c_transfer(&via_i2c_par[adap].adapter, &msgs, 1);
+	ret = i2c_transfer(&via_i2c_par[adap].adapter, &msgs, 1);
+	if (ret == 1)
+		ret = 0;
+	else if (ret >= 0)
+		ret = -EIO;
+
+	return ret;
 }
 
 int viafb_i2c_readbytes(u8 adap, u8 slave_addr, u8 index, u8 *buff, int buff_len)
 {
+	int ret;
 	u8 mm1[] = {0x00};
 	struct i2c_msg msgs[2];
 
@@ -156,7 +171,13 @@ int viafb_i2c_readbytes(u8 adap, u8 slav
 	mm1[0] = index;
 	msgs[0].len = 1; msgs[1].len = buff_len;
 	msgs[0].buf = mm1; msgs[1].buf = buff;
-	return i2c_transfer(&via_i2c_par[adap].adapter, msgs, 2);
+	ret = i2c_transfer(&via_i2c_par[adap].adapter, msgs, 2);
+	if (ret == 2)
+		ret = 0;
+	else if (ret >= 0)
+		ret = -EIO;
+
+	return ret;
 }
 
 /*


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