[i2c] Generalise i2c bit-bashing support to addressless devices

Some devices (e.g. the Atmel AT24C11) have no concept of a device
address; they respond to every device address and use this value as
the word address.  Some other devices use part of the device address
field to extend the word address field.

Generalise the i2c bit-bashing support to handle this by defining the
device address length and word address length as properties of an i2c
device.  The word address is assumed to overflow into the device
address field if the address used exceeds the width of the word
address field.

Also add a bus reset mechanism.  i2c chips don't usually have a reset
line, so rebooting the host will not clear any bizarre state that the
chip may be in.  We reset the bus by clocking SCL until we see SDA
high, at which point we know we can generate a start condition and
have it seen by all devices.  We then generate a stop condition to
leave the bus in a known state prior to use.

Finally, add some extra debugging messages to i2c_bit.c.

src/drivers/bitbash/i2c_bit.c

@@ -19,6 +19,7 @@
 #include <stddef.h>
 #include <stdint.h>
 #include <errno.h>
+#include <string.h>
 #include <assert.h>
 #include <unistd.h>
 #include <gpxe/bitbash.h>
@@ -49,6 +50,7 @@ static void i2c_delay ( void ) {
  * @v state		New state of SCL
  */
 static void setscl ( struct bit_basher *basher, int state ) {
+	DBG2 ( "%c", ( state ? '/' : '\\' ) );
 	write_bit ( basher, I2C_BIT_SCL, state );
 	i2c_delay();
 }
@@ -60,6 +62,7 @@ static void setscl ( struct bit_basher *basher, int state ) {
  * @v state		New state of SDA
  */
 static void setsda ( struct bit_basher *basher, int state ) {
+	DBG2 ( "%c", ( state ? '1' : '0' ) );
 	write_bit ( basher, I2C_BIT_SDA, state );
 	i2c_delay();
 }
@@ -71,7 +74,10 @@ static void setsda ( struct bit_basher *basher, int state ) {
  * @ret state		State of SDA
  */
 static int getsda ( struct bit_basher *basher ) {
-	return read_bit ( basher, I2C_BIT_SDA );
+	int state;
+	state = read_bit ( basher, I2C_BIT_SDA );
+	DBG2 ( "%c", ( state ? '+' : '-' ) );
+	return state;
 }
 
 /**
@@ -137,15 +143,20 @@ static void i2c_stop ( struct bit_basher *basher ) {
  */
 static int i2c_send_byte ( struct bit_basher *basher, uint8_t byte ) {
 	int i;
-	
+	int ack;
+
 	/* Send byte */
+	DBG2 ( "[send %02x]", byte );
 	for ( i = 8 ; i ; i-- ) {
 		i2c_send_bit ( basher, byte & 0x80 );
 		byte <<= 1;
 	}
 
 	/* Check for acknowledgement from slave */
-	return ( i2c_recv_bit ( basher ) == 0 ? 0 : -EIO );
+	ack = ( i2c_recv_bit ( basher ) == 0 );
+	DBG2 ( "%s", ( ack ? "[acked]" : "[not acked]" ) );
+
+	return ( ack ? 0 : -EIO );
 }
 
 /**
@@ -157,19 +168,20 @@ static int i2c_send_byte ( struct bit_basher *basher, uint8_t byte ) {
  * Receives a byte via the I2C bus and sends NACK to the slave device.
  */
 static uint8_t i2c_recv_byte ( struct bit_basher *basher ) {
-	uint8_t value = 0;
+	uint8_t byte = 0;
 	int i;
 
 	/* Receive byte */
 	for ( i = 8 ; i ; i-- ) {
-		value <<= 1;
-		value |= ( i2c_recv_bit ( basher ) & 0x1 );
+		byte <<= 1;
+		byte |= ( i2c_recv_bit ( basher ) & 0x1 );
 	}
 
 	/* Send NACK */
 	i2c_send_bit ( basher, 1 );
 
-	return value;
+	DBG2 ( "[rcvd %02x]", byte );
+	return byte;
 }
 
 /**
@@ -177,36 +189,75 @@ static uint8_t i2c_recv_byte ( struct bit_basher *basher ) {
  *
  * @v basher		Bit-bashing interface
  * @v i2cdev		I2C device
+ * @v offset		Starting offset within the device
  * @v direction		I2C_READ or I2C_WRITE
  * @ret rc		Return status code
  */
 static int i2c_select ( struct bit_basher *basher, struct i2c_device *i2cdev,
-			unsigned int direction ) {
+			unsigned int offset, unsigned int direction ) {
 	unsigned int address;
+	int shift;
+	unsigned int byte;
 	int rc;
 
 	i2c_start ( basher );
 
-	/* First byte of the address */
-	address = i2cdev->address;
-	if ( i2cdev->tenbit ) {
-		address |= I2C_TENBIT_ADDRESS;
-		address >>= 8;
-	}
-	if ( ( rc = i2c_send_byte ( basher, 
-				    ( ( address << 1 ) | direction ) ) ) != 0 )
-		return rc;
+	/* Calculate address to appear on bus */
+	address = ( ( ( i2cdev->dev_addr |
+			( offset >> ( 8 * i2cdev->word_addr_len ) ) ) << 1 )
+		    | direction );
 
-	/* Second byte of the address (10-bit addresses only) */
-	if ( i2cdev->tenbit ) {
-		if ( ( rc = i2c_send_byte ( basher,
-					    ( i2cdev->address & 0xff ) ) ) !=0)
+	/* Send address a byte at a time */
+	for ( shift = ( 8 * ( i2cdev->dev_addr_len - 1 ) ) ;
+	      shift >= 0 ; shift -= 8 ) {
+		byte = ( ( address >> shift ) & 0xff );
+		if ( ( rc = i2c_send_byte ( basher, byte ) ) != 0 )
 			return rc;
 	}
 
 	return 0;
 }
 
+/**
+ * Reset I2C bus
+ *
+ * @v basher		Bit-bashing interface
+ * @ret rc		Return status code
+ *
+ * i2c devices often don't have a reset line, so even a reboot or
+ * system power cycle is sometimes not enough to bring them back to a
+ * known state.
+ */
+static int i2c_reset ( struct bit_basher *basher ) {
+	unsigned int i;
+	int sda;
+
+	/* Clock through several cycles, waiting for an opportunity to
+	 * pull SDA low while SCL is high (which creates a start
+	 * condition).
+	 */
+	setscl ( basher, 0 );
+	setsda ( basher, 1 );
+	for ( i = 0 ; i < I2C_RESET_MAX_CYCLES ; i++ ) {
+		setscl ( basher, 1 );
+		sda = getsda ( basher );
+		if ( sda ) {
+			/* Now that the device will see a start, issue it */
+			i2c_start ( basher );
+			/* Stop the bus to leave it in a known good state */
+			i2c_stop ( basher );
+			DBGC ( basher, "I2CBIT %p reset after %d attempts\n",
+			       basher, ( i + 1 ) );
+			return 0;
+		}
+		setscl ( basher, 0 );
+	}
+
+	DBGC ( basher, "I2CBIT %p could not reset after %d attempts\n",
+	       basher, i );
+	return -ETIMEDOUT;
+}
+
 /**
  * Read data from I2C device via bit-bashing interface
  *
@@ -228,12 +279,14 @@ static int i2c_bit_read ( struct i2c_interface *i2c,
 	struct bit_basher *basher = &i2cbit->basher;
 	int rc = 0;
 
-	DBG ( "Reading from I2C device %x: ", i2cdev->address );
+	DBGC ( basher, "I2CBIT %p reading from device %x: ",
+	       basher, i2cdev->dev_addr );
 
-	while ( 1 ) {
+	for ( ; ; data++, offset++ ) {
 
 		/* Select device for writing */
-		if ( ( rc = i2c_select ( basher, i2cdev, I2C_WRITE ) ) != 0 )
+		if ( ( rc = i2c_select ( basher, i2cdev, offset,
+					 I2C_WRITE ) ) != 0 )
 			break;
 
 		/* Abort at end of data */
@@ -241,19 +294,20 @@ static int i2c_bit_read ( struct i2c_interface *i2c,
 			break;
 
 		/* Select offset */
-		if ( ( rc = i2c_send_byte ( basher, offset++ ) ) != 0 )
+		if ( ( rc = i2c_send_byte ( basher, offset ) ) != 0 )
 			break;
 		
 		/* Select device for reading */
-		if ( ( rc = i2c_select ( basher, i2cdev, I2C_READ ) ) != 0 )
+		if ( ( rc = i2c_select ( basher, i2cdev, offset,
+					 I2C_READ ) ) != 0 )
 			break;
 
 		/* Read byte */
-		*data++ = i2c_recv_byte ( basher );
-		DBG ( "%02x ", *(data - 1) );
+		*data = i2c_recv_byte ( basher );
+		DBGC ( basher, "%02x ", *data );
 	}
 	
-	DBG ( "%s\n", ( rc ? "failed" : "" ) );
+	DBGC ( basher, "%s\n", ( rc ? "failed" : "" ) );
 	i2c_stop ( basher );
 	return rc;
 }
@@ -279,12 +333,14 @@ static int i2c_bit_write ( struct i2c_interface *i2c,
 	struct bit_basher *basher = &i2cbit->basher;
 	int rc = 0;
 
-	DBG ( "Writing to I2C device %x: ", i2cdev->address );
+	DBGC ( basher, "I2CBIT %p writing to device %x: ",
+	       basher, i2cdev->dev_addr );
 
-	while ( 1 ) {
+	for ( ; ; data++, offset++ ) {
 
 		/* Select device for writing */
-		if ( ( rc = i2c_select ( basher, i2cdev, I2C_WRITE ) ) != 0 )
+		if ( ( rc = i2c_select ( basher, i2cdev, offset,
+					 I2C_WRITE ) ) != 0 )
 			break;
 		
 		/* Abort at end of data */
@@ -292,16 +348,16 @@ static int i2c_bit_write ( struct i2c_interface *i2c,
 			break;
 
 		/* Select offset */
-		if ( ( rc = i2c_send_byte ( basher, offset++ ) ) != 0 )
+		if ( ( rc = i2c_send_byte ( basher, offset ) ) != 0 )
 			break;
 		
 		/* Write data to device */
-		DBG ( "%02x ", *data );
-		if ( ( rc = i2c_send_byte ( basher, *data++ ) ) != 0 )
+		DBGC ( basher, "%02x ", *data );
+		if ( ( rc = i2c_send_byte ( basher, *data ) ) != 0 )
 			break;
 	}
 	
-	DBG ( "%s\n", ( rc ? "failed" : "" ) );
+	DBGC ( basher, "%s\n", ( rc ? "failed" : "" ) );
 	i2c_stop ( basher );
 	return rc;
 }
@@ -310,13 +366,26 @@ static int i2c_bit_write ( struct i2c_interface *i2c,
  * Initialise I2C bit-bashing interface
  *
  * @v i2cbit		I2C bit-bashing interface
+ * @v bash_op		Bit-basher operations
  */
-void init_i2c_bit_basher ( struct i2c_bit_basher *i2cbit ) {
+int init_i2c_bit_basher ( struct i2c_bit_basher *i2cbit,
+			  struct bit_basher_operations *bash_op ) {
 	struct bit_basher *basher = &i2cbit->basher;
-	
+	int rc;
+
+	/* Initialise data structures */
+	basher->op = bash_op;
 	assert ( basher->op->read != NULL );
 	assert ( basher->op->write != NULL );
 	i2cbit->i2c.read = i2c_bit_read;
 	i2cbit->i2c.write = i2c_bit_write;
-	i2c_stop ( basher );
+
+	/* Reset I2C bus */
+	if ( ( rc = i2c_reset ( basher ) ) != 0 ) {
+		DBGC ( basher, "I2CBIT %p could not reset I2C bus: %s\n",
+		       basher, strerror ( rc ) );
+		return rc;
+	}
+
+	return 0;
 }

src/drivers/net/etherfabric.c

@@ -1069,9 +1069,9 @@ static struct bit_basher_operations ef1002_basher_ops = {
 };
 
 static void ef1002_init_eeprom ( struct efab_nic *efab ) {
-	efab->ef1002_i2c.basher.op = &ef1002_basher_ops;
-	init_i2c_bit_basher ( &efab->ef1002_i2c );
-	efab->ef1002_eeprom.address = EF1_EEPROM_I2C_ID;
+	init_i2c_bit_basher ( &efab->ef1002_i2c,
+			      &ef1002_basher_ops );
+	init_i2c_eeprom ( &efab->ef1002_eeprom, EF1_EEPROM_I2C_ID );
 }
 
 /**

src/include/gpxe/i2c.h

@@ -8,6 +8,7 @@
  */
 
 #include <stdint.h>
+#include <gpxe/bitbash.h>
 
 /** An I2C device
  *
@@ -15,10 +16,35 @@
  * is accessed via an I2C interface.
  */
 struct i2c_device {
-	/** Address of this device */
-	unsigned int address;
-	/** Flag indicating a ten-bit address format */
-	int tenbit;
+	/** Address of this device
+	 *
+	 * The actual address sent on the bus will look like
+	 *
+	 *    <start> <device address> <word address overflow> <r/w>
+	 *
+	 * The "word address overflow" is any excess bits from the
+	 * word address, i.e. any portion that does not fit within the
+	 * defined word address length.
+	 */
+	unsigned int dev_addr;
+	/** Device address length, in bytes
+	 *
+	 * This is the number of bytes that comprise the device
+	 * address, defined to be the portion that terminates with the
+	 * read/write bit.
+	 */
+	unsigned int dev_addr_len;
+	/** Word adddress length, in bytes
+	 *
+	 * This is the number of bytes that comprise the word address,
+	 * defined to be the portion that starts after the read/write
+	 * bit and ends before the first data byte.
+	 *
+	 * For some devices, this length will be zero (i.e. the word
+	 * address is contained entirely within the "word address
+	 * overflow").
+	 */
+	unsigned int word_addr_len;
 };
 
 /** An I2C interface
@@ -91,6 +117,9 @@ enum {
 /** Delay required for bit-bashing operation */
 #define I2C_UDELAY 5
 
+/** Maximum number of cycles to use when attempting a bus reset */
+#define I2C_RESET_MAX_CYCLES 32
+
 /**
  * Check presence of I2C device
  *
@@ -106,6 +135,35 @@ static inline int i2c_check_presence ( struct i2c_interface *i2c,
 	return i2c->write ( i2c, i2cdev, 0, NULL, 0 );
 }
 
-extern void init_i2c_bit_basher ( struct i2c_bit_basher *i2cbit );
+extern int init_i2c_bit_basher ( struct i2c_bit_basher *i2cbit,
+				 struct bit_basher_operations *bash_op );
+
+/**
+ * Initialise generic I2C EEPROM device
+ *
+ * @v i2cdev		I2C device
+ */
+static inline __always_inline void
+init_i2c_eeprom ( struct i2c_device *i2cdev, unsigned int dev_addr ) {
+	i2cdev->dev_addr = dev_addr;
+	i2cdev->dev_addr_len = 1;
+	i2cdev->word_addr_len = 1;
+}
+
+/**
+ * Initialise Atmel AT24C11
+ *
+ * @v i2cdev		I2C device
+ */
+static inline __always_inline void
+init_at24c11 ( struct i2c_device *i2cdev ) {
+	/* This chip has no device address; it must be the only chip
+	 * on the bus.  The word address is contained entirely within
+	 * the device address field.
+	 */
+	i2cdev->dev_addr = 0;
+	i2cdev->dev_addr_len = 1;
+	i2cdev->word_addr_len = 0;
+}
 
 #endif /* _GPXE_I2C_H */