GIC: Add APIs to enable and disable interrupt

API documentation updated.

Change-Id: Ice7511f8df5356851001d2f7dc2a46cfe318f9ba
Co-authored-by: Yousuf A <yousuf.sait@arm.com>
Signed-off-by: Jeenu Viswambharan <jeenu.viswambharan@arm.com>
diff --git a/docs/platform-interrupt-controller-API.rst b/docs/platform-interrupt-controller-API.rst
index d0a2ad2..bea1a64 100644
--- a/docs/platform-interrupt-controller-API.rst
+++ b/docs/platform-interrupt-controller-API.rst
@@ -81,6 +81,36 @@
 the GIC *Set Active Register* to read and return the active status of the
 interrupt.
 
+Function: void plat_ic_enable_interrupt(unsigned int id); [optional]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+::
+
+    Argument : unsigned int
+    Return   : void
+
+This API should enable the interrupt ID specified by the first parameter,
+``id``. PEs in the system are expected to receive only enabled interrupts.
+
+In case of ARM standard platforms using GIC, the implementation of the API
+inserts barrier to make memory updates visible before enabling interrupt, and
+then writes to GIC *Set Enable Register* to enable the interrupt.
+
+Function: void plat_ic_disable_interrupt(unsigned int id); [optional]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+::
+
+    Argument : unsigned int
+    Return   : void
+
+This API should disable the interrupt ID specified by the first parameter,
+``id``. PEs in the system are not expected to receive disabled interrupts.
+
+In case of ARM standard platforms using GIC, the implementation of the API
+writes to GIC *Clear Enable Register* to disable the interrupt, and inserts
+barrier to make memory updates visible afterwards.
+
 ----
 
 *Copyright (c) 2017, ARM Limited and Contributors. All rights reserved.*