eeprom: at24: support reading the serial number for 24csxx

The chips from the at24cs family have two memory areas - a regular
read-write block and a read-only area containing the serial number.

The latter is visible on a different slave address (the address of the
rw memory block + 0x08). In order to access both blocks the user needs
to instantiate a regular at24c device for the rw block address and a
corresponding at24cs device on the serial number block address.

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@baylibre.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>

drivers/misc/eeprom/at24.c

@@ -134,16 +134,34 @@ static const struct i2c_device_id at24_ids[] = {
 	{ "24c00",	AT24_DEVICE_MAGIC(128 / 8,	AT24_FLAG_TAKE8ADDR) },
 	/* old variants can't be handled with this generic entry! */
 	{ "24c01",	AT24_DEVICE_MAGIC(1024 / 8,	0) },
+	{ "24cs01",	AT24_DEVICE_MAGIC(16,
+				AT24_FLAG_SERIAL | AT24_FLAG_READONLY) },
 	{ "24c02",	AT24_DEVICE_MAGIC(2048 / 8,	0) },
+	{ "24cs02",	AT24_DEVICE_MAGIC(16,
+				AT24_FLAG_SERIAL | AT24_FLAG_READONLY) },
 	/* spd is a 24c02 in memory DIMMs */
 	{ "spd",	AT24_DEVICE_MAGIC(2048 / 8,
 				AT24_FLAG_READONLY | AT24_FLAG_IRUGO) },
 	{ "24c04",	AT24_DEVICE_MAGIC(4096 / 8,	0) },
+	{ "24cs04",	AT24_DEVICE_MAGIC(16,
+				AT24_FLAG_SERIAL | AT24_FLAG_READONLY) },
 	/* 24rf08 quirk is handled at i2c-core */
 	{ "24c08",	AT24_DEVICE_MAGIC(8192 / 8,	0) },
+	{ "24cs08",	AT24_DEVICE_MAGIC(16,
+				AT24_FLAG_SERIAL | AT24_FLAG_READONLY) },
 	{ "24c16",	AT24_DEVICE_MAGIC(16384 / 8,	0) },
+	{ "24cs16",	AT24_DEVICE_MAGIC(16,
+				AT24_FLAG_SERIAL | AT24_FLAG_READONLY) },
 	{ "24c32",	AT24_DEVICE_MAGIC(32768 / 8,	AT24_FLAG_ADDR16) },
+	{ "24cs32",	AT24_DEVICE_MAGIC(16,
+				AT24_FLAG_ADDR16 |
+				AT24_FLAG_SERIAL |
+				AT24_FLAG_READONLY) },
 	{ "24c64",	AT24_DEVICE_MAGIC(65536 / 8,	AT24_FLAG_ADDR16) },
+	{ "24cs64",	AT24_DEVICE_MAGIC(16,
+				AT24_FLAG_ADDR16 |
+				AT24_FLAG_SERIAL |
+				AT24_FLAG_READONLY) },
 	{ "24c128",	AT24_DEVICE_MAGIC(131072 / 8,	AT24_FLAG_ADDR16) },
 	{ "24c256",	AT24_DEVICE_MAGIC(262144 / 8,	AT24_FLAG_ADDR16) },
 	{ "24c512",	AT24_DEVICE_MAGIC(524288 / 8,	AT24_FLAG_ADDR16) },
@@ -276,6 +294,59 @@ 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 +648,13 @@ 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;

include/linux/platform_data/at24.h

@@ -48,6 +48,7 @@ struct at24_platform_data {
 #define AT24_FLAG_READONLY	BIT(6)	/* sysfs-entry will be read-only */
 #define AT24_FLAG_IRUGO		BIT(5)	/* sysfs-entry will be world-readable */
 #define AT24_FLAG_TAKE8ADDR	BIT(4)	/* take always 8 addresses (24c00) */
+#define AT24_FLAG_SERIAL	BIT(3)	/* factory-programmed serial number */
 
 	void		(*setup)(struct nvmem_device *nvmem, void *context);
 	void		*context;