mfd: cros_ec: Instantiate properly CrOS FP MCU device

Support Fingerprint MCU as a special of CrOS EC devices. The current FP
MCU uses the same EC SPI protocol v3 as other CrOS EC devices on a SPI
bus.

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

Signed-off-by: Vincent Palatin <vpalatin@chromium.org>
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

@@ -419,6 +419,16 @@ static int ec_device_probe(struct platform_device *pdev)
 	device_initialize(&ec->class_dev);
 	cdev_init(&ec->cdev, &fops);
 
+	/* Check whether this is actually a Fingerprint MCU rather than an EC */
+	if (cros_ec_check_features(ec, EC_FEATURE_FINGERPRINT)) {
+		dev_info(dev, "CrOS Fingerprint MCU detected.\n");
+		/*
+		 * Help userspace differentiating ECs from FP MCU,
+		 * regardless of the probing order.
+		 */
+		ec_platform->ec_name = CROS_EC_DEV_FP_NAME;
+	}
+
 	/*
 	 * Check whether this is actually an Integrated Sensor Hub (ISH)
 	 * rather than an EC.

include/linux/mfd/cros_ec.h

@@ -23,6 +23,7 @@
 #include <linux/mutex.h>
 
 #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_ISH_NAME "cros_ish"