eeprom: ee1004: Instantiate jc42 devices for DIMMS implementing Rev.1 SPD

DDR4 DIMMS implementing SPD Annex L, Revision 1 do not implement SPD byte
14 (Module Temperature Sensor); this byte was only added in revision 2 of
the standard. This only applies to DDR4, not DDR4E or LPDDR4, since those
DDR types were only introduced in revision 3 of the standard.

Use this information to instantiate the jc42 device if the module is a DDR4
following SPD revision 1.0 and a device is detected at the expected thermal
sensor address, even if the Module Temperature Sensor byte suggests that
the thermal sensor is not supported.

Cc: Heiner Kallweit <hkallweit1@gmail.com>
Cc: Thomas Weißschuh <linux@weissschuh.net>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20240629173716.20389-2-linux@roeck-us.net
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/misc/eeprom/ee1004.c b/drivers/misc/eeprom/ee1004.c
index 140bcb2..d4aeeb2 100644 (file)
--- a/drivers/misc/eeprom/ee1004.c
+++ b/drivers/misc/eeprom/ee1004.c
@@ -186,14 +186,31 @@ static void ee1004_probe_temp_sensor(struct i2c_client *client)
        struct i2c_board_info info = { .type = "jc42" };
        unsigned short addr = 0x18 | (client->addr & 7);
        unsigned short addr_list[] = { addr, I2C_CLIENT_END };
-       u8 byte14;
+       u8 data[2];
        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)))
+       ret = ee1004_eeprom_read(client, data, 14, 1);
+       if (ret != 1)
                return;
 
+       if (!(data[0] & BIT(7))) {
+               /*
+                * If the SPD data suggests that there is no temperature
+                * sensor, it may still be there for SPD revision 1.0.
+                * See SPD Annex L, Revision 1 and 2, for details.
+                * Check DIMM type and SPD revision; if it is a DDR4
+                * with SPD revision 1.0, check the thermal sensor address
+                * and instantiate the jc42 driver if a chip is found at
+                * that address.
+                * It is not necessary to check if there is a chip at the
+                * temperature sensor address since i2c_new_scanned_device()
+                * will do that and return silently if no chip is found.
+                */
+               ret = ee1004_eeprom_read(client, data, 1, 2);
+               if (ret != 2 || data[0] != 0x10 || data[1] != 0x0c)
+                       return;
+       }
        i2c_new_scanned_device(client->adapter, &info, addr_list, NULL);
 }