linux-kernel - [PATCH 1/3] i2c: i801: refactor i801_block_transaction_byte_by

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Message-Id: <1325847502-17841-2-git-send-email-djkurtz@chromium.org>
Date:	Fri,  6 Jan 2012 18:58:20 +0800
From:	Daniel Kurtz <djkurtz@...omium.org>
To:	khali@...ux-fr.org, ben-linux@...ff.org, seth.heasley@...el.com,
	ben@...adent.org.uk, David.Woodhouse@...el.com,
	linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:	olofj@...omium.org, bleung@...omium.org,
	Daniel Kurtz <djkurtz@...omium.org>
Subject: [PATCH 1/3] i2c: i801: refactor i801_block_transaction_byte_by_byte

1) As a slight optimization, pull some logic out of the byte loop during
byte-by-byte transactions by just setting the I801_LAST_BYTE bit, as
defined in the i801 (PCH) datasheet, when reading the last byte of a
byte-by-byte I2C_SMBUS_READ.

2) Clear INTR after clearing BYTE_DONE per ICH10 datasheet [1] pg. 711:

  When the last byte of a block message is received, the host controller
sets DS. However, it does not set the INTR bit (and generate another
interrupt) until DS is cleared. Thus, for a block message of n bytes,
the ICH10 will generate n+1 interrupts.

3) If DEV_ERR is set in polling loop, abort the transaction and return
-ENXIO to the caller. DEV_ERR is set if the device does not respond with
an acknowledge, and the SMBus controller times out (minimum 25ms).

[1] http://www.intel.com/content/dam/doc/datasheet/io-controller-hub-10-family-datasheet.pdf

Signed-off-by: Daniel Kurtz <djkurtz@...omium.org>
---
 drivers/i2c/busses/i2c-i801.c |   45 ++++++++++++++++++++++++----------------
 1 files changed, 27 insertions(+), 18 deletions(-)

diff --git a/drivers/i2c/busses/i2c-i801.c b/drivers/i2c/busses/i2c-i801.c
index ab26840d..f3418cf 100644
--- a/drivers/i2c/busses/i2c-i801.c
+++ b/drivers/i2c/busses/i2c-i801.c
@@ -116,8 +116,7 @@
 #define I801_PROC_CALL		0x10	/* unimplemented */
 #define I801_BLOCK_DATA		0x14
 #define I801_I2C_BLOCK_DATA	0x18	/* ICH5 and later */
-#define I801_BLOCK_LAST		0x34
-#define I801_I2C_BLOCK_LAST	0x38	/* ICH5 and later */
+#define I801_LAST_BYTE		0x20
 #define I801_START		0x40
 #define I801_PEC_EN		0x80	/* ICH3 and later */
 
@@ -320,7 +319,7 @@ static int i801_block_transaction_by_block(struct i801_priv *priv,
 	}
 
 	status = i801_transaction(priv, I801_BLOCK_DATA | ENABLE_INT9 |
-				  I801_PEC_EN * hwpec);
+				  (hwpec ? I801_PEC_EN : 0));
 	if (status)
 		return status;
 
@@ -336,6 +335,10 @@ static int i801_block_transaction_by_block(struct i801_priv *priv,
 	return 0;
 }
 
+/*
+ * i2c write uses cmd=I801_BLOCK_DATA, I2C_EN=1
+ * i2c read uses cmd=I801_I2C_BLOCK_DATA
+ */
 static int i801_block_transaction_byte_by_byte(struct i801_priv *priv,
 					       union i2c_smbus_data *data,
 					       char read_write, int command,
@@ -358,19 +361,15 @@ static int i801_block_transaction_byte_by_byte(struct i801_priv *priv,
 		outb_p(data->block[1], SMBBLKDAT(priv));
 	}
 
+	if (command == I2C_SMBUS_I2C_BLOCK_DATA &&
+	    read_write == I2C_SMBUS_READ)
+		smbcmd = I801_I2C_BLOCK_DATA;
+	else
+		smbcmd = I801_BLOCK_DATA;
+
 	for (i = 1; i <= len; i++) {
-		if (i == len && read_write == I2C_SMBUS_READ) {
-			if (command == I2C_SMBUS_I2C_BLOCK_DATA)
-				smbcmd = I801_I2C_BLOCK_LAST;
-			else
-				smbcmd = I801_BLOCK_LAST;
-		} else {
-			if (command == I2C_SMBUS_I2C_BLOCK_DATA
-			 && read_write == I2C_SMBUS_READ)
-				smbcmd = I801_I2C_BLOCK_DATA;
-			else
-				smbcmd = I801_BLOCK_DATA;
-		}
+		if (i == len && read_write == I2C_SMBUS_READ)
+			smbcmd |= I801_LAST_BYTE;
 		outb_p(smbcmd | ENABLE_INT9, SMBHSTCNT(priv));
 
 		if (i == 1)
@@ -382,8 +381,9 @@ static int i801_block_transaction_byte_by_byte(struct i801_priv *priv,
 		do {
 			msleep(1);
 			status = inb_p(SMBHSTSTS(priv));
-		} while ((!(status & SMBHSTSTS_BYTE_DONE))
-			 && (timeout++ < MAX_TIMEOUT));
+		} while (!(status & SMBHSTSTS_BYTE_DONE) &&
+			 !(status & SMBHSTSTS_DEV_ERR) &&
+			 timeout++ < MAX_TIMEOUT);
 
 		result = i801_check_post(priv, status, timeout > MAX_TIMEOUT);
 		if (result < 0)
@@ -414,8 +414,17 @@ static int i801_block_transaction_byte_by_byte(struct i801_priv *priv,
 			outb_p(data->block[i+1], SMBBLKDAT(priv));
 
 		/* signals SMBBLKDAT ready */
-		outb_p(SMBHSTSTS_BYTE_DONE | SMBHSTSTS_INTR, SMBHSTSTS(priv));
+		outb_p(SMBHSTSTS_BYTE_DONE, SMBHSTSTS(priv));
+	}
+
+	/* Wait for command-completion interrupt so we can clear it */
+	timeout = 0;
+	status = inb_p(SMBHSTSTS(priv));
+	while (!(status & SMBHSTSTS_INTR) && timeout++ < MAX_TIMEOUT) {
+		msleep(1);
+		status = inb_p(SMBHSTSTS(priv));
 	}
+	outb_p(SMBHSTSTS_INTR, SMBHSTSTS(priv));
 
 	return 0;
 }
-- 
1.7.3.1

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