[PATCH] ARM: kernel: DT cpu map validity check helper function

[Lorenzo Pieralisi]

Since the introduction of /cpu nodes bindings for ARM and the
corresponding parse function arm_dt_init_cpu_maps(), the cpu_logical_map
and the number of possible CPUs are set according to the DT /cpu
nodes entries. Currently most of the existing ARM SMP platforms detect the
number of cores through HW probing in their .smp_init_cpus functions and set
the possible CPU mask accordingly.
This method should be upgraded so that the CPU counting mechanism will be
based on DT, keeping legacy HW probing mechanism as a fall back solution.

In order to implement this fall back solution mechanism, the ARM DT code
should provide a helper function to platforms to check if the cpu map
has been properly initialized through DT. If the check fails the
platform will resort to legacy HW based cores counting mechanism.

This patch implements a trivial flag and a helper function that platform
can call to check whether DT based cpu map initialization and cores count
were completed successfully.

Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi at arm.com>
---
 arch/arm/include/asm/prom.h | 10 ++++++++++
 arch/arm/kernel/devtree.c   |  5 +++++
 2 files changed, 15 insertions(+)

diff --git a/arch/arm/include/asm/prom.h b/arch/arm/include/asm/prom.h
index a219227..487614a 100644
--- a/arch/arm/include/asm/prom.h
+++ b/arch/arm/include/asm/prom.h
@@ -18,6 +18,15 @@
 extern struct machine_desc *setup_machine_fdt(unsigned int dt_phys);
 extern void arm_dt_memblock_reserve(void);
 extern void __init arm_dt_init_cpu_maps(void);
+/*
+ * Return true if cpu map initialization has been
+ * carried out correctly from DT
+ */
+static inline bool __init arm_dt_cpu_map_valid(void)
+{
+	extern bool valid_dt_cpu_map;
+	return valid_dt_cpu_map;
+}
 
 #else /* CONFIG_OF */
 
@@ -28,6 +37,7 @@ static inline struct machine_desc *setup_machine_fdt(unsigned int dt_phys)
 
 static inline void arm_dt_memblock_reserve(void) { }
 static inline void arm_dt_init_cpu_maps(void) { }
+static inline bool __init arm_dt_cpu_map_valid(void) { return false; }
 
 #endif /* CONFIG_OF */
 #endif /* ASMARM_PROM_H */
diff --git a/arch/arm/kernel/devtree.c b/arch/arm/kernel/devtree.c
index 70f1bde..c82af3b 100644
--- a/arch/arm/kernel/devtree.c
+++ b/arch/arm/kernel/devtree.c
@@ -62,6 +62,10 @@ void __init arm_dt_memblock_reserve(void)
 		memblock_reserve(base, size);
 	}
 }
+/*
+ * Export DT cpu map validity flag to platforms
+ */
+bool valid_dt_cpu_map __initdata;
 
 /*
  * arm_dt_init_cpu_maps - Function retrieves cpu nodes from the device tree
@@ -158,6 +162,7 @@ void __init arm_dt_init_cpu_maps(void)
 	 * a reg property, the DT CPU list can be considered valid and the
 	 * logical map created in smp_setup_processor_id() can be overridden
 	 */
+	valid_dt_cpu_map = true;
 	for (i = 0; i < cpuidx; i++) {
 		set_cpu_possible(i, true);
 		cpu_logical_map(i) = tmp_map[i];
-- 
1.7.12