mfd: cros_ec: Instantiate properly CrOS Touchpad MCU device

Support Touchpad MCU as a special of CrOS EC devices. The current
Touchpad MCU is used on Eve Chromebook and used the same protocol as
other CrOS EC devices.

When a MCU has touchpad support (aka EC_FEATURE_TOUCHPAD), it is
instantiated as a special CrOS EC device with device name 'cros_tp'. So
regardless of the probing order between the actual cros_ec and cros_tp,
the userspace and other kernel drivers should not confuse them.

Signed-off-by: Wei-Ning Huang <wnhuang@google.com>
Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

drivers/mfd/cros_ec_dev.c

@@ -442,6 +442,16 @@ static int ec_device_probe(struct platform_device *pdev)
 		ec_platform->ec_name = CROS_EC_DEV_ISH_NAME;
 	}
 
+	/* Check whether this is actually a Touchpad MCU rather than an EC */
+	if (cros_ec_check_features(ec, EC_FEATURE_TOUCHPAD)) {
+		dev_info(dev, "CrOS Touchpad MCU detected.\n");
+		/*
+		 * Help userspace differentiating ECs from TP MCU,
+		 * regardless of the probing order.
+		 */
+		ec_platform->ec_name = CROS_EC_DEV_TP_NAME;
+	}
+
 	/*
 	 * Add the class device
 	 * Link to the character device for creating the /dev entry

include/linux/mfd/cros_ec.h

@@ -25,6 +25,7 @@
 #define CROS_EC_DEV_NAME "cros_ec"
 #define CROS_EC_DEV_FP_NAME "cros_fp"
 #define CROS_EC_DEV_PD_NAME "cros_pd"
+#define CROS_EC_DEV_TP_NAME "cros_tp"
 #define CROS_EC_DEV_ISH_NAME "cros_ish"
 
 /*