[PATCH RFC] eeprom: ee1004: add support for temperature sensor

[Heiner Kallweit <hkallweit1@gmail.com>]

Jean and me are discussing how to best instantiate temperature sensors
that can be found on RAM modules. First idea was to extend
i2c_register_spd() but I think reading the "temp sensor present" flag
from SPD can't be properly done from an i2c core level.
Therefore, for DDR4, do it from the ee1004 driver.

The temp sensor i2c address can be derived from the SPD i2c address,
so I think we can directly instantiate the device and don't have to
probe for it.
If the temp sensor has been instantiated already by other means
(e.g. class-based auto-detection), then the busy-check in 
i2c_new_client_device will detect this.

Link: https://www.spinics.net/lists/linux-i2c/msg65963.html
Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
---
 drivers/misc/eeprom/ee1004.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/drivers/misc/eeprom/ee1004.c b/drivers/misc/eeprom/ee1004.c
index a1acd7713..4bce8f9d9 100644
--- a/drivers/misc/eeprom/ee1004.c
+++ b/drivers/misc/eeprom/ee1004.c
@@ -158,6 +158,22 @@ static struct bin_attribute *ee1004_attrs[] = {
 
 BIN_ATTRIBUTE_GROUPS(ee1004);
 
+static void ee1004_probe_temp_sensor(struct i2c_client *client)
+{
+	struct i2c_board_info info = { .type = "jc42" };
+	u8 byte14;
+	int ret;
+
+	/* byte 14, bit 7 is set if temp sensor is present */
+	ret = ee1004_eeprom_read(client, &byte14, 14, 1);
+	if (ret != 1 || !(byte14 & BIT(7)))
+		return;
+
+	info.addr = 0x18 | (client->addr & 7);
+
+	i2c_new_client_device(client->adapter, &info);
+}
+
 static void ee1004_cleanup(int idx)
 {
 	if (--ee1004_dev_count == 0)
@@ -204,6 +220,9 @@ static int ee1004_probe(struct i2c_client *client)
 		err = -EOPNOTSUPP;
 		goto err_clients;
 	}
+
+	ee1004_probe_temp_sensor(client);
+
 	mutex_unlock(&ee1004_bus_lock);
 
 	dev_info(&client->dev,
-- 
2.42.1