power: supply: sbs-battery: chromebook workaround for PEC

Looks like the I2C tunnel implementation from Chromebook's
embedded controller does not handle PEC correctly. Fix this
by disabling PEC for batteries behind those I2C tunnels as
a workaround.

Note, that some Chromebooks actually have been reported to
have working PEC support (with I2C tunnel). Since the problem
has not yet been fully understood this simply reverts all
Chromebooks to not use PEC for now.

Reported-by: "Milan P. Stanić" <mps@arvanta.net>
Reported-by: Vicente Bergas <vicencb@gmail.com>
CC: Enric Balletbo i Serra <enric.balletbo@collabora.com>
Fixes: 7222bd603d ("power: supply: sbs-battery: add PEC support")
Tested-by: Vicente Bergas <vicencb@gmail.com>
Tested-by: "Milan P. Stanić" <mps@arvanta.net>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>

drivers/power/supply/sbs-battery.c

@@ -280,6 +280,12 @@ static int sbs_update_presence(struct sbs_info *chip, bool is_present)
 	else
 		client->flags &= ~I2C_CLIENT_PEC;
 
+	if (of_device_is_compatible(client->dev.parent->of_node, "google,cros-ec-i2c-tunnel")
+	    && client->flags & I2C_CLIENT_PEC) {
+		dev_info(&client->dev, "Disabling PEC because of broken Cros-EC implementation\n");
+		client->flags &= ~I2C_CLIENT_PEC;
+	}
+
 	dev_dbg(&client->dev, "PEC: %s\n", (client->flags & I2C_CLIENT_PEC) ?
 		"enabled" : "disabled");