[PATCH v2] i2c: i801: Fix handling SMBHSTCNT_PEC_EN

[Heiner Kallweit <hkallweit1@gmail.com>]

Bit SMBHSTCNT_PEC_EN is used only if software calculates the CRC and
uses register SMBPEC. This is not supported by the driver, it supports
hw-calculation of CRC only (using bit SMBAUXSTS_CRCE). The chip spec
states the following, therefore never set bit SMBHSTCNT_PEC_EN.

Chapter SMBus CRC Generation and Checking
If the AAC bit is set in the Auxiliary Control register, the PCH
automatically calculates and drives CRC at the end of the transmitted
packet for write cycles, and will check the CRC for read cycles. It will
not transmit the contents of the PEC register for CRC. The PEC bit must
not be set in the Host Control register. If this bit is set, unspecified
behavior will result.

This patch is based solely on the specification and compile-tested only,
because I have no PEC-capable devices.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Tested-by: Jean Delvare <jdelvare@suse.de>
---
v2:
- further simplified the change in i801_block_transaction_by_block
- added comment to the change in i801_setup_hstcfg
---
 drivers/i2c/busses/i2c-i801.c | 27 +++++++++++----------------
 1 file changed, 11 insertions(+), 16 deletions(-)

diff --git a/drivers/i2c/busses/i2c-i801.c b/drivers/i2c/busses/i2c-i801.c
index aa3f60e69..92ec291c0 100644
--- a/drivers/i2c/busses/i2c-i801.c
+++ b/drivers/i2c/busses/i2c-i801.c
@@ -503,19 +503,16 @@ static int i801_transaction(struct i801_priv *priv, int xact)
 
 static int i801_block_transaction_by_block(struct i801_priv *priv,
 					   union i2c_smbus_data *data,
-					   char read_write, int command,
-					   int hwpec)
+					   char read_write, int command)
 {
-	int i, len;
-	int status;
-	int xact = hwpec ? SMBHSTCNT_PEC_EN : 0;
+	int i, len, status, xact;
 
 	switch (command) {
 	case I2C_SMBUS_BLOCK_PROC_CALL:
-		xact |= I801_BLOCK_PROC_CALL;
+		xact = I801_BLOCK_PROC_CALL;
 		break;
 	case I2C_SMBUS_BLOCK_DATA:
-		xact |= I801_BLOCK_DATA;
+		xact = I801_BLOCK_DATA;
 		break;
 	default:
 		return -EOPNOTSUPP;
@@ -665,8 +662,7 @@ static irqreturn_t i801_isr(int irq, void *dev_id)
  */
 static int i801_block_transaction_byte_by_byte(struct i801_priv *priv,
 					       union i2c_smbus_data *data,
-					       char read_write, int command,
-					       int hwpec)
+					       char read_write, int command)
 {
 	int i, len;
 	int smbcmd;
@@ -764,9 +760,8 @@ static int i801_set_block_buffer_mode(struct i801_priv *priv)
 }
 
 /* Block transaction function */
-static int i801_block_transaction(struct i801_priv *priv,
-				  union i2c_smbus_data *data, char read_write,
-				  int command, int hwpec)
+static int i801_block_transaction(struct i801_priv *priv, union i2c_smbus_data *data,
+				  char read_write, int command)
 {
 	int result = 0;
 	unsigned char hostc;
@@ -802,11 +797,11 @@ static int i801_block_transaction(struct i801_priv *priv,
 	 && i801_set_block_buffer_mode(priv) == 0)
 		result = i801_block_transaction_by_block(priv, data,
 							 read_write,
-							 command, hwpec);
+							 command);
 	else
 		result = i801_block_transaction_byte_by_byte(priv, data,
 							     read_write,
-							     command, hwpec);
+							     command);
 
 	if (command == I2C_SMBUS_I2C_BLOCK_DATA
 	 && read_write == I2C_SMBUS_WRITE) {
@@ -917,8 +912,7 @@ static s32 i801_access(struct i2c_adapter *adap, u16 addr,
 		       SMBAUXCTL(priv));
 
 	if (block)
-		ret = i801_block_transaction(priv, data, read_write, size,
-					     hwpec);
+		ret = i801_block_transaction(priv, data, read_write, size);
 	else
 		ret = i801_transaction(priv, xact);
 
@@ -1690,6 +1684,7 @@ static void i801_setup_hstcfg(struct i801_priv *priv)
 	unsigned char hstcfg = priv->original_hstcfg;
 
 	hstcfg &= ~SMBHSTCFG_I2C_EN;	/* SMBus timing */
+	hstcfg &= ~SMBHSTCNT_PEC_EN;	/* Disable software PEC */
 	hstcfg |= SMBHSTCFG_HST_EN;
 	pci_write_config_byte(priv->pci_dev, SMBHSTCFG, hstcfg);
 }
-- 
2.32.0