Candidate fix for SCL getting stretched when high resulting in
slave timeouts.

Signed-off-by: Jean Delvare <khali-PUYAD+kWke1g9hUCZPvPmw@public.gmane.org>
---
 drivers/i2c/algos/i2c-algo-bit.c |   34 ++++++++++++++++++++++++++++++----
 include/linux/i2c-algo-bit.h     |    3 +++
 2 files changed, 33 insertions(+), 4 deletions(-)

--- linux-2.6.27.orig/drivers/i2c/algos/i2c-algo-bit.c	2010-12-15 15:25:12.000000000 +0100
+++ linux-2.6.27/drivers/i2c/algos/i2c-algo-bit.c	2010-12-15 15:25:26.000000000 +0100
@@ -30,6 +30,7 @@
 #include <linux/sched.h>
 #include <linux/i2c.h>
 #include <linux/i2c-algo-bit.h>
+#include <linux/spinlock.h>
 
 
 /* ----- global defines ----------------------------------------------- */
@@ -131,12 +132,17 @@ static void i2c_start(struct i2c_algo_bi
 
 static void i2c_repstart(struct i2c_algo_bit_data *adap)
 {
+	unsigned long flags;
+
 	/* assert: scl is low */
 	sdahi(adap);
+	spin_lock_irqsave(&adap->lockscl, flags);
 	sclhi(adap);
 	setsda(adap, 0);
 	udelay(adap->udelay);
-	scllo(adap);
+	setscl(adap, 0);
+	spin_unlock_irqrestore(&adap->lockscl, flags);
+	udelay(adap->udelay / 2);
 }
 
 
@@ -164,13 +170,16 @@ static int i2c_outb(struct i2c_adapter *
 	int sb;
 	int ack;
 	struct i2c_algo_bit_data *adap = i2c_adap->algo_data;
+	unsigned long flags;
 
 	/* assert: scl is low */
 	for (i = 7; i >= 0; i--) {
 		sb = (c >> i) & 1;
 		setsda(adap, sb);
 		udelay((adap->udelay + 1) / 2);
+		spin_lock_irqsave(&adap->lockscl, flags);
 		if (sclhi(adap) < 0) { /* timed out */
+			spin_unlock_irqrestore(&adap->lockscl, flags);
 			bit_dbg(1, &i2c_adap->dev, "i2c_outb: 0x%02x, "
 				"timeout at bit #%d\n", (int)c, i);
 			return -ETIMEDOUT;
@@ -181,10 +190,14 @@ static int i2c_outb(struct i2c_adapter *
 		 * Report a unique code, so higher level code can retry
 		 * the whole (combined) message and *NOT* issue STOP.
 		 */
-		scllo(adap);
+		setscl(adap, 0);
+		spin_unlock_irqrestore(&adap->lockscl, flags);
+		udelay(adap->udelay / 2);
 	}
 	sdahi(adap);
+	spin_lock_irqsave(&adap->lockscl, flags);
 	if (sclhi(adap) < 0) { /* timeout */
+		spin_unlock_irqrestore(&adap->lockscl, flags);
 		bit_dbg(1, &i2c_adap->dev, "i2c_outb: 0x%02x, "
 			"timeout at ack\n", (int)c);
 		return -ETIMEDOUT;
@@ -194,10 +207,13 @@ static int i2c_outb(struct i2c_adapter *
 	 * NAK (usually to report problems with the data we wrote).
 	 */
 	ack = !getsda(adap);    /* ack: sda is pulled low -> success */
+	setscl(adap, 0);
+	spin_unlock_irqrestore(&adap->lockscl, flags);
+	udelay(adap->udelay / 2);
+
 	bit_dbg(2, &i2c_adap->dev, "i2c_outb: 0x%02x %s\n", (int)c,
 		ack ? "A" : "NA");
 
-	scllo(adap);
 	return ack;
 	/* assert: scl is low (sda undef) */
 }
@@ -210,11 +226,14 @@ static int i2c_inb(struct i2c_adapter *i
 	int i;
 	unsigned char indata = 0;
 	struct i2c_algo_bit_data *adap = i2c_adap->algo_data;
+	unsigned long flags;
 
 	/* assert: scl is low */
 	sdahi(adap);
 	for (i = 0; i < 8; i++) {
+		spin_lock_irqsave(&adap->lockscl, flags);
 		if (sclhi(adap) < 0) { /* timeout */
+			spin_unlock_irqrestore(&adap->lockscl, flags);
 			bit_dbg(1, &i2c_adap->dev, "i2c_inb: timeout at bit "
 				"#%d\n", 7 - i);
 			return -ETIMEDOUT;
@@ -223,6 +242,7 @@ static int i2c_inb(struct i2c_adapter *i
 		if (getsda(adap))
 			indata |= 0x01;
 		setscl(adap, 0);
+		spin_unlock_irqrestore(&adap->lockscl, flags);
 		udelay(i == 7 ? adap->udelay / 2 : adap->udelay);
 	}
 	/* assert: scl is low */
@@ -385,16 +405,21 @@ static int sendbytes(struct i2c_adapter 
 static int acknak(struct i2c_adapter *i2c_adap, int is_ack)
 {
 	struct i2c_algo_bit_data *adap = i2c_adap->algo_data;
+	unsigned long flags;
 
 	/* assert: sda is high */
 	if (is_ack)		/* send ack */
 		setsda(adap, 0);
 	udelay((adap->udelay + 1) / 2);
+	spin_lock_irqsave(&adap->lockscl, flags);
 	if (sclhi(adap) < 0) {	/* timeout */
+		spin_unlock_irqrestore(&adap->lockscl, flags);
 		dev_err(&i2c_adap->dev, "readbytes: ack/nak timeout\n");
 		return -ETIMEDOUT;
 	}
-	scllo(adap);
+	setscl(adap, 0);
+	spin_unlock_irqrestore(&adap->lockscl, flags);
+	udelay(adap->udelay / 2);
 	return 0;
 }
 
@@ -603,6 +628,7 @@ static int i2c_bit_prepare_bus(struct i2
 	}
 
 	/* register new adapter to i2c module... */
+	spin_lock_init(&bit_adap->lockscl);
 	adap->algo = &i2c_bit_algo;
 
 	adap->timeout = 100;	/* default values, should	*/
--- linux-2.6.27.orig/include/linux/i2c-algo-bit.h	2010-12-15 15:25:12.000000000 +0100
+++ linux-2.6.27/include/linux/i2c-algo-bit.h	2010-12-15 15:25:44.000000000 +0100
@@ -24,6 +24,8 @@
 #ifndef _LINUX_I2C_ALGO_BIT_H
 #define _LINUX_I2C_ALGO_BIT_H
 
+#include <linux/spinlock.h>
+
 /* --- Defines for bit-adapters ---------------------------------------	*/
 /*
  * This struct contains the hw-dependent functions of bit-style adapters to
@@ -36,6 +38,7 @@ struct i2c_algo_bit_data {
 	void (*setscl) (void *data, int state);
 	int  (*getsda) (void *data);
 	int  (*getscl) (void *data);
+	spinlock_t lockscl;
 
 	/* local settings */
 	int udelay;		/* half clock cycle time in us,