The at24cs series EEPROM chips have an additional read-only memory area,
that is visible on a different i2c slave address. Tie it up with a dummy
device.

Signed-off-by: Bartosz Golaszewski <bgolaszew...@baylibre.com>
---
 drivers/misc/eeprom/at24.c | 30 ++++++++++++++++++++++++++----
 1 file changed, 26 insertions(+), 4 deletions(-)

diff --git a/drivers/misc/eeprom/at24.c b/drivers/misc/eeprom/at24.c
index 5d7c090..08cc327 100644
--- a/drivers/misc/eeprom/at24.c
+++ b/drivers/misc/eeprom/at24.c
@@ -103,6 +103,8 @@ MODULE_PARM_DESC(write_timeout, "Time (in ms) to try writes 
(default 25)");
 
 #define AT24_BITMASK(x) (BIT(x) - 1)
 
+#define AT24CS_SERIAL_ADDR(addr) (addr + 0x08)
+
 /* create non-zero magic value for given eeprom parameters */
 #define AT24_DEVICE_MAGIC(_len, _flags)                \
        ((1 << AT24_SIZE_FLAGS | (_flags))              \
@@ -558,6 +560,8 @@ static int at24_probe(struct i2c_client *client, const 
struct i2c_device_id *id)
 
        if (chip.flags & AT24_FLAG_TAKE8ADDR)
                num_addresses = 8;
+       else if (chip.flags & AT24_FLAG_SERIAL)
+               num_addresses = 2;
        else
                num_addresses = DIV_ROUND_UP(chip.byte_len,
                        (chip.flags & AT24_FLAG_ADDR16) ? 65536 : 256);
@@ -616,12 +620,30 @@ static int at24_probe(struct i2c_client *client, const 
struct i2c_device_id *id)
        at24->client[0] = client;
 
        /* use dummy devices for multiple-address chips */
-       for (i = 1; i < num_addresses; i++) {
-               at24->client[i] = i2c_new_dummy(client->adapter,
+       if (at24->chip.flags & AT24_FLAG_TAKE8ADDR) {
+               for (i = 1; i < num_addresses; i++) {
+                       at24->client[i] = i2c_new_dummy(client->adapter,
+                                                       client->addr + i);
+                       if (!at24->client[i]) {
+                               dev_err(&client->dev,
+                                       "address 0x%02x unavailable\n",
                                        client->addr + i);
-               if (!at24->client[i]) {
+                               err = -EADDRINUSE;
+                               goto err_clients;
+                       }
+               }
+       }
+
+       /*
+        * at24cs series tie up an additional address for the memory area
+        * contining the serial number
+        */
+       if (at24->chip.flags & AT24_FLAG_SERIAL) {
+               at24->client[1] = i2c_new_dummy(client->adapter,
+                                       AT24CS_SERIAL_ADDR(client->addr));
+               if (!at24->client[1]) {
                        dev_err(&client->dev, "address 0x%02x unavailable\n",
-                                       client->addr + i);
+                               AT24CS_SERIAL_ADDR(client->addr));
                        err = -EADDRINUSE;
                        goto err_clients;
                }
-- 
2.1.4

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