Commit 6150e5e1 authored by Guenter Roeck's avatar Guenter Roeck Committed by Greg Kroah-Hartman
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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: default avatarGuenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20240629173716.20389-2-linux@roeck-us.net


Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 249b4dea

drivers/misc/eeprom/ee1004.c

+20 −3
Original line number Diff line number Diff line
@@ -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);

}