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 and assign it
to at24->read_func if the chip allows serial number read operations
and the driver was passed the relevant flag for this device.
Signed-off-by: Bartosz Golaszewski <bgolaszewski@xxxxxxxxxxxx>
---
drivers/misc/eeprom/at24.c | 62 ++++++++++++++++++++++++++++++++++++++++++++--
1 file changed, 60 insertions(+), 2 deletions(-)
diff --git a/drivers/misc/eeprom/at24.c b/drivers/misc/eeprom/at24.c
index 6acf35a..29bbdad 100644
--- a/drivers/misc/eeprom/at24.c
+++ b/drivers/misc/eeprom/at24.c
@@ -276,6 +276,59 @@ static ssize_t at24_eeprom_read_i2c(struct at24_data *at24, char *buf,
return -ETIMEDOUT;
}
+static ssize_t at24_eeprom_read_serial(struct at24_data *at24, char *buf,
+ unsigned int offset, size_t count)
+{
+ unsigned long timeout, read_time;
+ struct i2c_client *client;
+ 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;
+
+ loop_until_timeout(timeout, read_time) {
+ status = i2c_transfer(client->adapter, msg, 2);
+ if (status == 2)
+ return count;
+ }
+
+ return -ETIMEDOUT;
+}
+
/*
* Note that if the hardware write-protect pin is pulled high, the whole
* chip is normally write protected. But there are plenty of product
@@ -577,8 +630,13 @@ static int at24_probe(struct i2c_client *client, const struct i2c_device_id *id)
at24->chip = chip;
at24->num_addresses = num_addresses;
- at24->read_func = at24->use_smbus ? at24_eeprom_read_smbus
- : at24_eeprom_read_i2c;
+ if (chip.flags & AT24_FLAG_SERIAL) {
+ at24->read_func = at24_eeprom_read_serial;
+ } else {
+ at24->read_func = at24->use_smbus ? at24_eeprom_read_smbus
+ : at24_eeprom_read_i2c;
+ }
+
if (at24->use_smbus) {
if (at24->use_smbus_write == I2C_SMBUS_I2C_BLOCK_DATA)
at24->write_func = at24_eeprom_write_smbus_block;
--
2.7.4
--
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