mfd: cros_ec: differentiate SCP from EC by feature bit

System Companion Processor (SCP) is Cortex M4 co-processor on some
MediaTek platform that can run EC-style firmware. Since a SCP and EC
would both exist on a system, and use the cros_ec_dev driver, we need to
differentiate between them for the userspace, or they would both be
registered at /dev/cros_ec, causing a conflict.

Signed-off-by: Pi-Hsun Shih <pihsun@chromium.org>
Acked-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

drivers/mfd/cros_ec_dev.c

@@ -459,6 +459,16 @@ static int ec_device_probe(struct platform_device *pdev)
 		ec_platform->ec_name = CROS_EC_DEV_TP_NAME;
 	}
 
+	/* Check whether this is actually a SCP rather than an EC. */
+	if (cros_ec_check_features(ec, EC_FEATURE_SCP)) {
+		dev_info(dev, "CrOS SCP MCU detected.\n");
+		/*
+		 * Help userspace differentiating ECs from SCP,
+		 * regardless of the probing order.
+		 */
+		ec_platform->ec_name = CROS_EC_DEV_SCP_NAME;
+	}
+
 	/*
 	 * Add the class device
 	 * Link to the character device for creating the /dev entry

include/linux/mfd/cros_ec.h

@@ -27,6 +27,7 @@
 #define CROS_EC_DEV_PD_NAME "cros_pd"
 #define CROS_EC_DEV_TP_NAME "cros_tp"
 #define CROS_EC_DEV_ISH_NAME "cros_ish"
+#define CROS_EC_DEV_SCP_NAME "cros_scp"
 
 /*
  * The EC is unresponsive for a time after a reboot command.  Add a