platform/x86: dell-*: Add a generic dell-laptop notifier chain

There are several cases where events handled in one of the dell-* drivers
need to be propagated to another dell-* driver.

This commit adds 3 generic functions:
dell_laptop_register_notifier()
dell_laptop_unregister_notifier()
dell_laptop_call_notifier()

It currently only defines 1 action:
DELL_LAPTOP_KBD_BACKLIGHT_BRIGHTNESS_CHANGED

Which is intended to propagate kbd_backlight_brightness_changed wmi
events from dell-wmi to dell-laptop (which contains the actual kbd
backlight driver).

These functions are put in dell-smbios as both dell-wmi and dell-laptop
use smbios functions and I do not want to put the notifier head in
either driver, as that will make the 2 drivers depend on each other.
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Pali Rohár <pali.rohar@gmail.com>
Signed-off-by: Darren Hart (VMware) <dvhart@infradead.org>

drivers/platform/x86/dell-smbios.c

@@ -105,6 +105,26 @@ struct calling_interface_token *dell_smbios_find_token(int tokenid)
 }
 EXPORT_SYMBOL_GPL(dell_smbios_find_token);
 
+static BLOCKING_NOTIFIER_HEAD(dell_laptop_chain_head);
+
+int dell_laptop_register_notifier(struct notifier_block *nb)
+{
+	return blocking_notifier_chain_register(&dell_laptop_chain_head, nb);
+}
+EXPORT_SYMBOL_GPL(dell_laptop_register_notifier);
+
+int dell_laptop_unregister_notifier(struct notifier_block *nb)
+{
+	return blocking_notifier_chain_unregister(&dell_laptop_chain_head, nb);
+}
+EXPORT_SYMBOL_GPL(dell_laptop_unregister_notifier);
+
+void dell_laptop_call_notifier(unsigned long action, void *data)
+{
+	blocking_notifier_call_chain(&dell_laptop_chain_head, action, data);
+}
+EXPORT_SYMBOL_GPL(dell_laptop_call_notifier);
+
 static void __init parse_da_table(const struct dmi_header *dm)
 {
 	/* Final token is a terminator, so we don't want to copy it */

drivers/platform/x86/dell-smbios.h

@@ -16,6 +16,8 @@
 #ifndef _DELL_SMBIOS_H_
 #define _DELL_SMBIOS_H_
 
+struct notifier_block;
+
 /* This structure will be modified by the firmware when we enter
  * system management mode, hence the volatiles */
 
@@ -43,4 +45,13 @@ void dell_smbios_release_buffer(void);
 void dell_smbios_send_request(int class, int select);
 
 struct calling_interface_token *dell_smbios_find_token(int tokenid);
+
+enum dell_laptop_notifier_actions {
+	DELL_LAPTOP_KBD_BACKLIGHT_BRIGHTNESS_CHANGED,
+};
+
+int dell_laptop_register_notifier(struct notifier_block *nb);
+int dell_laptop_unregister_notifier(struct notifier_block *nb);
+void dell_laptop_call_notifier(unsigned long action, void *data);
+
 #endif