[i2c] [patch 2.6.24-rc1-git] i2c-algo-bit, don't yield()

[David Brownell]

On Tuesday 06 November 2007, Jean Delvare wrote:
> 	This automatic retry thing is misimplemented in at least
> two bus drivers, and causes delays for everyone (e.g. when framebuffer
> drivers probe for EDID EEPROMs). That's enough harm to warrant a swift
> removal. If anybody really cares, we'll discuss the matter with them
> when they complain.

OK ... here's a patch removing it from i2c-algo-bit
(and thence its users).

- Dave

=============
Remove the "retry address stage" mechanism from i2c-algo-bit.  That
mechanism is not something that upper level code can rely on; hardly
any I2C adapter drivers implement it, much less do it correctly.
Plus the notion itself is dubious.

Return any actual fault code returned in preferece to -EREMOTEIO, when
trying to address a specific device.

Signed-off-by: David Brownell <dbrownell at users.sourceforge.net>
---
 drivers/i2c/algos/i2c-algo-bit.c |   54 ++++++++++++---------------------------
 1 files changed, 17 insertions(+), 37 deletions(-)

--- a/drivers/i2c/algos/i2c-algo-bit.c	2007-11-14 21:36:34.000000000 -0800
+++ b/drivers/i2c/algos/i2c-algo-bit.c	2007-11-14 21:36:34.000000000 -0800
@@ -309,36 +309,17 @@ bailout:
 /* ----- Utility functions
  */
 
-/* try_address tries to contact a chip for a number of
- * times before it gives up.
+/* try_address tries to contact a chip.  SMBus devices are required
+ * to respond; I2C devices don't need to, if they're too busy.
+ *
  * return values:
  * 1 chip answered
  * 0 chip did not answer
- * -x transmission error
+ * -x transmission error (or lost arbitration)
  */
-static int try_address(struct i2c_adapter *i2c_adap,
-		       unsigned char addr, int retries)
+static int try_address(struct i2c_adapter *i2c_adap, unsigned char addr)
 {
-	struct i2c_algo_bit_data *adap = i2c_adap->algo_data;
-	int i, ret = -1;
-
-	for (i = 0; i <= retries; i++) {
-		ret = i2c_outb(i2c_adap, addr);
-		if (ret == 1 || i == retries)
-			break;
-		bit_dbg(3, &i2c_adap->dev, "emitting stop condition\n");
-		i2c_stop(adap);
-		udelay(adap->udelay);
-		yield();
-		bit_dbg(3, &i2c_adap->dev, "emitting start condition\n");
-		i2c_start(adap);
-	}
-	if (i && ret)
-		bit_dbg(1, &i2c_adap->dev, "Used %d tries to %s client at "
-			"0x%02x: %s\n", i + 1,
-			addr & 1 ? "read from" : "write to", addr >> 1,
-			ret == 1 ? "success" : "failed, timeout?");
-	return ret;
+	return i2c_outb(i2c_adap, addr);
 }
 
 static int sendbytes(struct i2c_adapter *i2c_adap, struct i2c_msg *msg)
@@ -465,27 +446,25 @@ static int bit_doAddress(struct i2c_adap
 	struct i2c_algo_bit_data *adap = i2c_adap->algo_data;
 
 	unsigned char addr;
-	int ret, retries;
-
-	retries = nak_ok ? 0 : i2c_adap->retries;
+	int ret;
 
 	if (flags & I2C_M_TEN) {
 		/* a ten bit address */
 		addr = 0xf0 | ((msg->addr >> 7) & 0x03);
 		bit_dbg(2, &i2c_adap->dev, "addr0: %d\n", addr);
 		/* try extended address code...*/
-		ret = try_address(i2c_adap, addr, retries);
+		ret = try_address(i2c_adap, addr);
 		if ((ret != 1) && !nak_ok)  {
 			dev_err(&i2c_adap->dev,
 				"died at extended address code\n");
-			return -EREMOTEIO;
+			goto fail;
 		}
 		/* the remaining 8 bit address */
 		ret = i2c_outb(i2c_adap, msg->addr & 0x7f);
 		if ((ret != 1) && !nak_ok) {
 			/* the chip did not ack / xmission error occurred */
 			dev_err(&i2c_adap->dev, "died at 2nd address code\n");
-			return -EREMOTEIO;
+			goto fail;
 		}
 		if (flags & I2C_M_RD) {
 			bit_dbg(3, &i2c_adap->dev, "emitting repeated "
@@ -493,11 +472,11 @@ static int bit_doAddress(struct i2c_adap
 			i2c_repstart(adap);
 			/* okay, now switch into reading mode */
 			addr |= 0x01;
-			ret = try_address(i2c_adap, addr, retries);
+			ret = try_address(i2c_adap, addr);
 			if ((ret != 1) && !nak_ok) {
 				dev_err(&i2c_adap->dev,
 					"died at repeated address code\n");
-				return -EREMOTEIO;
+				goto fail;
 			}
 		}
 	} else {		/* normal 7bit address	*/
@@ -506,12 +485,14 @@ static int bit_doAddress(struct i2c_adap
 			addr |= 1;
 		if (flags & I2C_M_REV_DIR_ADDR)
 			addr ^= 1;
-		ret = try_address(i2c_adap, addr, retries);
+		ret = try_address(i2c_adap, addr);
 		if ((ret != 1) && !nak_ok)
-			return -EREMOTEIO;
+			goto fail;
 	}
 
 	return 0;
+fail:
+	return (ret < 0) ? ret : -EREMOTEIO;
 }
 
 static int bit_xfer(struct i2c_adapter *i2c_adap,
@@ -605,8 +586,7 @@ static int i2c_bit_prepare_bus(struct i2
 	/* register new adapter to i2c module... */
 	adap->algo = &i2c_bit_algo;
 
-	adap->timeout = 100;	/* default values, should	*/
-	adap->retries = 3;	/* be replaced by defines	*/
+	adap->timeout = 100;	/* default value */
 
 	return 0;
 }