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 <bgolaszewski@xxxxxxxxxxxx>
---
drivers/misc/eeprom/at24.c | 71 ++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 71 insertions(+)
diff --git a/drivers/misc/eeprom/at24.c b/drivers/misc/eeprom/at24.c
index 08cc327..6182f47 100644
--- a/drivers/misc/eeprom/at24.c
+++ b/drivers/misc/eeprom/at24.c
@@ -163,6 +163,77 @@ static struct i2c_client *at24_translate_offset(struct at24_data *at24,
return at24->client[i];
}
+static int __attribute__((unused)) at24cs_eeprom_serial_read(
+ struct at24_data *at24,
+ char *buf, unsigned offset,
+ size_t count)
+{
+ unsigned long timeout, read_time;
+ struct i2c_client *client;
+ struct i2c_msg msg[2];
+ u8 addrbuf[2];
+ int status;
+
+ mutex_lock(&at24->lock);
+
+ client = at24->client[1];
+
+ 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;
+
+ /*
+ * Reads fail if the previous write didn't complete yet. We may
+ * loop a few times until this one succeeds, waiting at least
+ * long enough for one entire page write to work.
+ */
+ timeout = jiffies + msecs_to_jiffies(write_timeout);
+ do {
+ read_time = jiffies;
+ status = i2c_transfer(client->adapter, msg, 2);
+ if (status == 2) {
+ mutex_unlock(&at24->lock);
+ return count;
+ }
+
+ /* REVISIT: at HZ=100, this is sloooow */
+ msleep(1);
+ } while (time_before(read_time, timeout));
+
+ mutex_unlock(&at24->lock);
+
+ return -ETIMEDOUT;
+}
+
static ssize_t at24_eeprom_read(struct at24_data *at24, char *buf,
unsigned offset, size_t count)
{
--
2.1.4
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