dev/i2c_eeprom.c: Use negative offset when addr>0xff is mangled with dev addr

On some I2C eeproms which require addresses >1B, the remaining bits are mangled together with the i2c device address. Thus a negative offset_bytes is introduced to cover these cases. The absolute value refers to the amount of mangled bits. E.g. -2 would mean, that the address consists of 10 bits, with two being joined with the i2c device address.

dev/i2c_eeprom.c

@@ -7,10 +7,27 @@
  * Released according to the GNU GPL, version 2 or any later version.
  */
 
+#include <stdlib.h>
+
 #include "board.h"
 #include "dev/bb_i2c.h"
 #include "dev/i2c_eeprom.h"
 
+static uint8_t i2c_get_address_for_virtual_devices( struct i2c_eeprom_device *dev, int offset)
+{
+	uint8_t addr = dev->addr;
+
+	/*
+	 * See explanation in i2c_eeprom.h for negative offsets
+	 */
+	if (dev->offset_bytes < 0) {
+		uint8_t offset_bits_mask = (1 << (-dev->offset_bytes)) - 1;
+		addr = dev->addr | ((offset >> 8) & offset_bits_mask);
+	}
+
+	return addr;
+}
+
 int i2c_eeprom_create( struct i2c_eeprom_device *dev, struct i2c_bus *bus, uint8_t i2c_addr, int offset_bytes )
 {
 	dev->bus = bus;
@@ -23,9 +40,10 @@ int i2c_eeprom_read(struct i2c_eeprom_device *dev, int offset, void *buf, int co
 {
 	int i;
 	unsigned char *cb = buf;
+	uint8_t addr = i2c_get_address_for_virtual_devices(dev, offset);
 
 	bb_i2c_start(dev->bus);
-	if (bb_i2c_put_byte(dev->bus, dev->addr << 1) < 0) {
+	if (bb_i2c_put_byte(dev->bus, addr << 1) < 0) {
 		bb_i2c_stop(dev->bus);
 		return -1;
 	}
@@ -35,7 +53,7 @@ int i2c_eeprom_read(struct i2c_eeprom_device *dev, int offset, void *buf, int co
 	
 	bb_i2c_put_byte(dev->bus, offset & 0xff);
 	bb_i2c_repeat_start(dev->bus);
-	bb_i2c_put_byte(dev->bus, (dev->addr << 1) | 1);
+	bb_i2c_put_byte(dev->bus, (addr << 1) | 1);
 	for (i = 0; i < count - 1; ++i) {
 		bb_i2c_get_byte(dev->bus, cb, 0);
 		cb++;
@@ -51,11 +69,14 @@ int i2c_eeprom_write(struct i2c_eeprom_device *dev, int offset, void *buf, int c
 {
 	int i, busy;
 	unsigned char *cb = buf;
+	uint8_t addr;
 
 	for (i = 0; i < count; i++) {
 		bb_i2c_start(dev->bus);
 
-		if (bb_i2c_put_byte(dev->bus, dev->addr << 1) < 0) {
+		addr = i2c_get_address_for_virtual_devices(dev, offset);
+
+		if (bb_i2c_put_byte(dev->bus, addr << 1) < 0) {
 			bb_i2c_stop(dev->bus);
 			return -1;
 		}
@@ -70,7 +91,7 @@ int i2c_eeprom_write(struct i2c_eeprom_device *dev, int offset, void *buf, int c
 
 		do {		/* wait until the chip becomes ready */
 			bb_i2c_start(dev->bus);
-			busy = bb_i2c_put_byte(dev->bus, dev->addr << 1);
+			busy = bb_i2c_put_byte(dev->bus, addr << 1);
 			bb_i2c_stop(dev->bus);
 		} while (busy);
 
@@ -81,11 +102,14 @@ int i2c_eeprom_write(struct i2c_eeprom_device *dev, int offset, void *buf, int c
 int i2c_eeprom_erase(struct i2c_eeprom_device *dev, int offset, int count)
 {
 	int i, busy;
+	uint8_t addr;
 
 	for (i = 0; i < count; i++) {
 		bb_i2c_start(dev->bus);
 
-		if (bb_i2c_put_byte(dev->bus, dev->addr << 1) < 0) {
+		addr = i2c_get_address_for_virtual_devices(dev, offset);
+
+		if (bb_i2c_put_byte(dev->bus, addr << 1) < 0) {
 			bb_i2c_stop(dev->bus);
 			return -1;
 		}
@@ -100,7 +124,7 @@ int i2c_eeprom_erase(struct i2c_eeprom_device *dev, int offset, int count)
 
 		do {		/* wait until the chip becomes ready */
 			bb_i2c_start(dev->bus);
-			busy = bb_i2c_put_byte(dev->bus, dev->addr << 1);
+			busy = bb_i2c_put_byte(dev->bus, addr << 1);
 			bb_i2c_stop(dev->bus);
 		} while (busy);