platform/chrome: cros_ec: Add a flag to track registration state

Introduce a `registered` flag to the `struct cros_ec_device` to allow
callers to determine if the device has been fully registered and is
ready for use.

This is a preparatory step to prevent race conditions where other drivers
might try to access the device before it is fully registered or after
it has been unregistered.

Link: https://lore.kernel.org/r/20250828083601.856083-5-tzungbi@kernel.org
Signed-off-by: Tzung-Bi Shih <tzungbi@kernel.org>

Author: Tzung-Bi Shih

drivers/platform/chrome/cros_ec.c

@@ -9,6 +9,7 @@
  * battery charging and regulator control, firmware update.
  */
 
+#include <linux/cleanup.h>
 #include <linux/interrupt.h>
 #include <linux/module.h>
 #include <linux/of_platform.h>
@@ -316,6 +317,9 @@ int cros_ec_register(struct cros_ec_device *ec_dev)
 			goto exit;
 	}
 
+	scoped_guard(mutex, &ec_dev->lock)
+		ec_dev->registered = true;
+
 	dev_info(dev, "Chrome EC device registered\n");
 
 	/*
@@ -343,6 +347,9 @@ EXPORT_SYMBOL(cros_ec_register);
  */
 void cros_ec_unregister(struct cros_ec_device *ec_dev)
 {
+	scoped_guard(mutex, &ec_dev->lock)
+		ec_dev->registered = false;
+
 	if (ec_dev->mkbp_event_supported)
 		blocking_notifier_chain_unregister(&ec_dev->event_notifier,
 						   &ec_dev->notifier_ready);

drivers/platform/chrome/cros_ec_proto.c

@@ -3,6 +3,7 @@
 //
 // Copyright (C) 2015 Google, Inc
 
+#include <linux/cleanup.h>
 #include <linux/delay.h>
 #include <linux/device.h>
 #include <linux/limits.h>
@@ -1153,5 +1154,19 @@ int cros_ec_get_cmd_versions(struct cros_ec_device *ec_dev, u16 cmd)
 }
 EXPORT_SYMBOL_GPL(cros_ec_get_cmd_versions);
 
+/**
+ * cros_ec_device_registered - Return if the ec_dev is registered.
+ *
+ * @ec_dev: EC device
+ *
+ * Return: true if registered.  Otherwise, false.
+ */
+bool cros_ec_device_registered(struct cros_ec_device *ec_dev)
+{
+	guard(mutex)(&ec_dev->lock);
+	return ec_dev->registered;
+}
+EXPORT_SYMBOL_GPL(cros_ec_device_registered);
+
 MODULE_LICENSE("GPL");
 MODULE_DESCRIPTION("ChromeOS EC communication protocol helpers");

include/linux/platform_data/cros_ec_proto.h

@@ -128,6 +128,7 @@ struct cros_ec_command {
  * @dout_size: Size of dout buffer to allocate (zero to use static dout).
  * @wake_enabled: True if this device can wake the system from sleep.
  * @suspended: True if this device had been suspended.
+ * @registered: True if this device had been registered.
  * @cmd_xfer: Send command to EC and get response.
  *            Returns the number of bytes received if the communication
  *            succeeded, but that doesn't mean the EC was happy with the
@@ -186,6 +187,7 @@ struct cros_ec_device {
 	int dout_size;
 	bool wake_enabled;
 	bool suspended;
+	bool registered;
 	int (*cmd_xfer)(struct cros_ec_device *ec,
 			struct cros_ec_command *msg);
 	int (*pkt_xfer)(struct cros_ec_device *ec,
@@ -278,6 +280,8 @@ int cros_ec_cmd_readmem(struct cros_ec_device *ec_dev, u8 offset, u8 size, void
 
 int cros_ec_get_cmd_versions(struct cros_ec_device *ec_dev, u16 cmd);
 
+bool cros_ec_device_registered(struct cros_ec_device *ec_dev);
+
 /**
  * cros_ec_get_time_ns() - Return time in ns.
  *