The at24cs series EEPROM chips have an additional read-only memory area containing a factory pre-programmed serial number. In order to access it, one has to perform a dummy write before reading the serial number bytes.
Add a function that allows to access the serial number. Signed-off-by: Bartosz Golaszewski <[email protected]> --- drivers/misc/eeprom/at24.c | 59 ++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 59 insertions(+) diff --git a/drivers/misc/eeprom/at24.c b/drivers/misc/eeprom/at24.c index bc5be1e..fda5c56 100644 --- a/drivers/misc/eeprom/at24.c +++ b/drivers/misc/eeprom/at24.c @@ -159,6 +159,65 @@ static struct i2c_client *at24_translate_offset(struct at24_data *at24, return at24->client[i]; } +static ssize_t __attribute__((unused)) +at24cs_serial_read(struct at24_data *at24, + char *buf, loff_t off, size_t count) +{ + unsigned long timeout, read_time; + struct i2c_client *client; + unsigned int offset = off; + struct i2c_msg msg[2]; + u8 addrbuf[2]; + int status; + + client = at24_translate_offset(at24, &offset); + + memset(msg, 0, sizeof(msg)); + msg[0].addr = client->addr; + msg[0].buf = addrbuf; + + /* + * The address pointer of the device is shared between the regular + * EEPROM array and the serial number block. The dummy write (part of + * the sequential read protocol) ensures the address pointer is reset + * to the desired position. + */ + if (at24->chip.flags & AT24_FLAG_ADDR16) { + /* + * For 16 bit address pointers, the word address must contain + * a '10' sequence in bits 11 and 10 regardless of the + * intended position of the address pointer. + */ + addrbuf[0] = 0x08; + addrbuf[1] = offset; + msg[0].len = 2; + } else { + /* + * Otherwise the word address must begin with a '10' sequence, + * regardless of the intended address. + */ + addrbuf[0] = 0x80 + offset; + msg[0].len = 1; + } + + msg[1].addr = client->addr; + msg[1].flags = I2C_M_RD; + msg[1].buf = buf; + msg[1].len = count; + + timeout = jiffies + msecs_to_jiffies(write_timeout); + do { + read_time = jiffies; + status = i2c_transfer(client->adapter, msg, 2); + if (status == 2) + return count; + + usleep_range(1000, 1500); + } while (time_before(read_time, timeout)); + + return -ETIMEDOUT; +} + static ssize_t at24_eeprom_read(struct at24_data *at24, char *buf, unsigned offset, size_t count) { -- 2.7.4
