i2c-i801: Consolidate polling

(Based on earlier work by Daniel Kurtz.)

Come up with a consistent, driver-wide strategy for event polling. For
intermediate steps of byte-by-byte block transactions, check for
BYTE_DONE or any error flag being set. At the end of every transaction
(regardless of PEC being used), check for both BUSY being cleared and
INTR or any error flag being set. This ensures proper action for all
transaction types.
Signed-off-by: Jean Delvare <khali@linux-fr.org>
Cc: Daniel Kurtz <djkurtz@chromium.org>

drivers/i2c/busses/i2c-i801.c

@@ -206,13 +206,17 @@ static int i801_check_pre(struct i801_priv *priv)
 	return 0;
 }
 
-/* Convert the status register to an error code, and clear it. */
-static int i801_check_post(struct i801_priv *priv, int status, int timeout)
+/*
+ * Convert the status register to an error code, and clear it.
+ * Note that status only contains the bits we want to clear, not the
+ * actual register value.
+ */
+static int i801_check_post(struct i801_priv *priv, int status)
 {
 	int result = 0;
 
 	/* If the SMBus is still busy, we give up */
-	if (timeout) {
+	if (unlikely(status < 0)) {
 		dev_err(&priv->pci_dev->dev, "Transaction timeout\n");
 		/* try to stop the current command */
 		dev_dbg(&priv->pci_dev->dev, "Terminating the current operation\n");
@@ -245,64 +249,68 @@ static int i801_check_post(struct i801_priv *priv, int status, int timeout)
 		dev_dbg(&priv->pci_dev->dev, "Lost arbitration\n");
 	}
 
-	if (result) {
-		/* Clear error flags */
-		outb_p(status & STATUS_FLAGS, SMBHSTSTS(priv));
-		status = inb_p(SMBHSTSTS(priv)) & STATUS_FLAGS;
-		if (status) {
-			dev_warn(&priv->pci_dev->dev, "Failed clearing status "
-				 "flags at end of transaction (%02x)\n",
-				 status);
-		}
-	}
+	/* Clear status flags except BYTE_DONE, to be cleared by caller */
+	outb_p(status, SMBHSTSTS(priv));
 
 	return result;
 }
 
-static int i801_transaction(struct i801_priv *priv, int xact)
+/* Wait for BUSY being cleared and either INTR or an error flag being set */
+static int i801_wait_intr(struct i801_priv *priv)
 {
-	int status;
-	int result;
 	int timeout = 0;
-
-	result = i801_check_pre(priv);
-	if (result < 0)
-		return result;
-
-	/* the current contents of SMBHSTCNT can be overwritten, since PEC,
-	 * SMBSCMD are passed in xact */
-	outb_p(xact | SMBHSTCNT_START, SMBHSTCNT(priv));
+	int status;
 
 	/* We will always wait for a fraction of a second! */
 	do {
 		usleep_range(250, 500);
 		status = inb_p(SMBHSTSTS(priv));
-	} while ((status & SMBHSTSTS_HOST_BUSY) && (timeout++ < MAX_RETRIES));
-
-	result = i801_check_post(priv, status, timeout > MAX_RETRIES);
-	if (result < 0)
-		return result;
+	} while (((status & SMBHSTSTS_HOST_BUSY) ||
+		  !(status & (STATUS_ERROR_FLAGS | SMBHSTSTS_INTR))) &&
+		 (timeout++ < MAX_RETRIES));
 
-	outb_p(SMBHSTSTS_INTR, SMBHSTSTS(priv));
-	return 0;
+	if (timeout > MAX_RETRIES) {
+		dev_dbg(&priv->pci_dev->dev, "INTR Timeout!\n");
+		return -ETIMEDOUT;
+	}
+	return status & (STATUS_ERROR_FLAGS | SMBHSTSTS_INTR);
 }
 
-/* wait for INTR bit as advised by Intel */
-static void i801_wait_hwpec(struct i801_priv *priv)
+/* Wait for either BYTE_DONE or an error flag being set */
+static int i801_wait_byte_done(struct i801_priv *priv)
 {
 	int timeout = 0;
 	int status;
 
+	/* We will always wait for a fraction of a second! */
 	do {
 		usleep_range(250, 500);
 		status = inb_p(SMBHSTSTS(priv));
-	} while ((!(status & SMBHSTSTS_INTR))
-		 && (timeout++ < MAX_RETRIES));
+	} while (!(status & (STATUS_ERROR_FLAGS | SMBHSTSTS_BYTE_DONE)) &&
+		 (timeout++ < MAX_RETRIES));
 
-	if (timeout > MAX_RETRIES)
-		dev_dbg(&priv->pci_dev->dev, "PEC Timeout!\n");
+	if (timeout > MAX_RETRIES) {
+		dev_dbg(&priv->pci_dev->dev, "BYTE_DONE Timeout!\n");
+		return -ETIMEDOUT;
+	}
+	return status & STATUS_ERROR_FLAGS;
+}
+
+static int i801_transaction(struct i801_priv *priv, int xact)
+{
+	int status;
+	int result;
+
+	result = i801_check_pre(priv);
+	if (result < 0)
+		return result;
+
+	/* the current contents of SMBHSTCNT can be overwritten, since PEC,
+	 * SMBSCMD are passed in xact */
+	outb_p(xact | SMBHSTCNT_START, SMBHSTCNT(priv));
 
-	outb_p(status & STATUS_FLAGS, SMBHSTSTS(priv));
+	status = i801_wait_intr(priv);
+	return i801_check_post(priv, status);
 }
 
 static int i801_block_transaction_by_block(struct i801_priv *priv,
@@ -353,7 +361,6 @@ static int i801_block_transaction_byte_by_byte(struct i801_priv *priv,
 	int smbcmd;
 	int status;
 	int result;
-	int timeout;
 
 	result = i801_check_pre(priv);
 	if (result < 0)
@@ -381,17 +388,9 @@ static int i801_block_transaction_byte_by_byte(struct i801_priv *priv,
 			outb_p(inb(SMBHSTCNT(priv)) | SMBHSTCNT_START,
 			       SMBHSTCNT(priv));
 
-		/* We will always wait for a fraction of a second! */
-		timeout = 0;
-		do {
-			usleep_range(250, 500);
-			status = inb_p(SMBHSTSTS(priv));
-		} while (!(status & (SMBHSTSTS_BYTE_DONE | STATUS_ERROR_FLAGS))
-			 && (timeout++ < MAX_RETRIES));
-
-		result = i801_check_post(priv, status, timeout > MAX_RETRIES);
-		if (result < 0)
-			return result;
+		status = i801_wait_byte_done(priv);
+		if (status)
+			goto exit;
 
 		if (i == 1 && read_write == I2C_SMBUS_READ
 		 && command != I2C_SMBUS_I2C_BLOCK_DATA) {
@@ -418,10 +417,12 @@ 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));
 	}
 
-	return 0;
+	status = i801_wait_intr(priv);
+exit:
+	return i801_check_post(priv, status);
 }
 
 static int i801_set_block_buffer_mode(struct i801_priv *priv)
@@ -476,9 +477,6 @@ static int i801_block_transaction(struct i801_priv *priv,
 							     read_write,
 							     command, hwpec);
 
-	if (result == 0 && hwpec)
-		i801_wait_hwpec(priv);
-
 	if (command == I2C_SMBUS_I2C_BLOCK_DATA
 	 && read_write == I2C_SMBUS_WRITE) {
 		/* restore saved configuration register value */