Call platform_is_primary_cpu() only from reset handler

The purpose of platform_is_primary_cpu() is to determine after reset
(BL1 or BL3-1 with reset handler) if the current CPU must follow the
cold boot path (primary CPU), or wait in a safe state (secondary CPU)
until the primary CPU has finished the system initialization.

This patch removes redundant calls to platform_is_primary_cpu() in
subsequent bootloader entrypoints since the reset handler already
guarantees that code is executed exclusively on the primary CPU.

Additionally, this patch removes the weak definition of
platform_is_primary_cpu(), so the implementation of this function
becomes mandatory. Removing the weak symbol avoids other
bootloaders accidentally picking up an invalid definition in case the
porting layer makes the real function available only to BL1.

The define PRIMARY_CPU is no longer mandatory in the platform porting
because platform_is_primary_cpu() hides the implementation details
(for instance, there may be platforms that report the primary CPU in
a system register). The primary CPU definition in FVP has been moved
to fvp_def.h.

The porting guide has been updated accordingly.

Fixes ARM-software/tf-issues#219

Change-Id: If675a1de8e8d25122b7fef147cb238d939f90b5e

1 files changed, 11 insertions, 16 deletions

diff --git a/docs/porting-guide.md b/docs/porting-guide.md
index c711590..db2bad8 100644
--- a/docs/porting-guide.md
+++ b/docs/porting-guide.md
@@ -150,11 +150,6 @@ file is found in [plat/fvp/include/platform_def.h].
     Defines the total number of nodes in the affinity heirarchy at all affinity
     levels used by the platform.
 
-*   **#define : PRIMARY_CPU**
-
-    Defines the `MPIDR` of the primary CPU on the platform. This value is used
-    after a cold boot to distinguish between primary and secondary CPUs.
-
 *   **#define : TZROM_BASE**
 
     Defines the base address of secure ROM on the platform, where the BL1 binary
@@ -360,6 +355,17 @@ requires them.
 This function fulfills requirement 2 above.
 
 
+### Function : platform_is_primary_cpu() [mandatory]
+
+    Argument : unsigned long
+    Return   : unsigned int
+
+This function identifies a CPU by its `MPIDR`, which is passed as the argument,
+to determine whether this CPU is the primary CPU or a secondary CPU. A return
+value of zero indicates that the CPU is not the primary CPU, while a non-zero
+return value indicates that the CPU is the primary CPU.
+
+
 ### Function : platform_mem_init() [mandatory]
 
     Argument : void
@@ -398,17 +404,6 @@ maximum of 4 CPUs:
     cluster_id = 8-bit value in MPIDR at affinity level 1
 
 
-### Function : platform_is_primary_cpu()
-
-    Argument : unsigned long
-    Return   : unsigned int
-
-This function identifies a CPU by its `MPIDR`, which is passed as the argument,
-to determine whether this CPU is the primary CPU or a secondary CPU. A return
-value of zero indicates that the CPU is not the primary CPU, while a non-zero
-return value indicates that the CPU is the primary CPU.
-
-
 ### Function : platform_set_stack()
 
     Argument : unsigned long