ARM: kernel: add logical mappings look-up

In ARM SMP systems the MPIDR register ([23:0] bits) is used to uniquely
identify CPUs.

In order to retrieve the logical CPU index corresponding to a given
MPIDR value and guarantee a consistent translation throughout the kernel,
this patch adds a look-up based on the MPIDR[23:0] so that kernel subsystems
can use it whenever the logical cpu index corresponding to a given MPIDR
value is needed.

Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Acked-by: Will Deacon <will.deacon@arm.com>
Acked-by: Nicolas Pitre <nico@linaro.org>

arch/arm/include/asm/smp_plat.h

@@ -5,6 +5,9 @@
 #ifndef __ASMARM_SMP_PLAT_H
 #define __ASMARM_SMP_PLAT_H
 
+#include <linux/cpumask.h>
+#include <linux/err.h>
+
 #include <asm/cputype.h>
 
 /*
@@ -48,5 +51,19 @@ static inline int cache_ops_need_broadcast(void)
  */
 extern int __cpu_logical_map[];
 #define cpu_logical_map(cpu)	__cpu_logical_map[cpu]
+/*
+ * Retrieve logical cpu index corresponding to a given MPIDR[23:0]
+ *  - mpidr: MPIDR[23:0] to be used for the look-up
+ *
+ * Returns the cpu logical index or -EINVAL on look-up error
+ */
+static inline int get_logical_index(u32 mpidr)
+{
+	int cpu;
+	for (cpu = 0; cpu < nr_cpu_ids; cpu++)
+		if (cpu_logical_map(cpu) == mpidr)
+			return cpu;
+	return -EINVAL;
+}
 
 #endif