Add platform API for reset handling

This patch adds an optional platform API (plat_reset_handler) which allows the
platform to perform any actions immediately after a cold or warm reset
e.g. implement errata workarounds. The function is called with MMU and caches
turned off. This API is weakly defined and does nothing by default but can be
overriden by a platform with a strong definition.

Change-Id: Ib0acdccbd24bc756528a8bd647df21e8d59707ff

docs/porting-guide.md

@@ -460,6 +460,20 @@ that these constants are not related to any architectural exception code; they
 are just an ARM Trusted Firmware convention.
 
 
+### Function : plat_reset_handler()
+
+    Argument : void
+    Return   : void
+
+A platform may need to do additional initialization after reset. This function
+allows the platform to do the platform specific intializations. Platform
+specific errata workarounds could also be implemented here. The api should
+preserve the value in x10 register as it is used by the caller to store the
+return address.
+
+The default implementation doesn't do anything.
+
+
 3.  Modifications specific to a Boot Loader stage
 -------------------------------------------------
 

lib/cpus/aarch64/cpu_helpers.S

@@ -47,6 +47,8 @@
 func reset_handler
 	mov	x10, x30
 
+	bl	plat_reset_handler
+
 	/* Get the matching cpu_ops pointer */
 	bl	get_cpu_ops_ptr
 #if ASM_ASSERTION
@@ -60,6 +62,7 @@ func reset_handler
 	blr	x2
 1:
 	ret	x10
+
 #endif /* IMAGE_BL1 || (IMAGE_BL31 && RESET_TO_BL31) */
 
 	/*

plat/common/aarch64/platform_helpers.S

@@ -38,6 +38,7 @@
 	.weak	plat_report_exception
 	.weak	plat_crash_console_init
 	.weak	plat_crash_console_putc
+	.weak	plat_reset_handler
 
 	/* -----------------------------------------------------
 	 *  int platform_get_core_pos(int mpidr);
@@ -84,3 +85,11 @@ func plat_crash_console_init
 	 */
 func plat_crash_console_putc
 	ret
+
+	/* -----------------------------------------------------
+	 * Placeholder function which should be redefined by
+	 * each platform. This function should preserve x10.
+	 * -----------------------------------------------------
+	 */
+func plat_reset_handler
+	ret