MIPS: introduce cpu_coherent_mask

Add a mask of CPUs which are currently known to be operating coherently.
This is setup initially to be all present CPUs, but in a subsequent
patch CPUs in a MIPS Coherent Processing System will be cleared in this
mask as they enter non-coherent idle states. This will be used in order
to determine when a CPU within a CPS system may need to be powered back
up, but may also be used in future to optimise away wakeups for cache
operations or TLB invalidations.
Signed-off-by: Paul Burton <paul.burton@imgtec.com>

arch/mips/include/asm/smp.h

@@ -46,6 +46,9 @@ extern int __cpu_logical_map[NR_CPUS];
 
 extern volatile cpumask_t cpu_callin_map;
 
+/* Mask of CPUs which are currently definitely operating coherently */
+extern cpumask_t cpu_coherent_mask;
+
 extern void asmlinkage smp_bootstrap(void);
 
 /*

arch/mips/kernel/smp.c

@@ -66,6 +66,8 @@ EXPORT_SYMBOL(cpu_sibling_map);
 /* representing cpus for which sibling maps can be computed */
 static cpumask_t cpu_sibling_setup_map;
 
+cpumask_t cpu_coherent_mask;
+
 static inline void set_cpu_sibling_map(int cpu)
 {
 	int i;
@@ -124,6 +126,7 @@ asmlinkage void start_secondary(void)
 	cpu = smp_processor_id();
 	cpu_data[cpu].udelay_val = loops_per_jiffy;
 
+	cpu_set(cpu, cpu_coherent_mask);
 	notify_cpu_starting(cpu);
 
 	set_cpu_online(cpu, true);
@@ -186,6 +189,7 @@ void __init smp_prepare_cpus(unsigned int max_cpus)
 #ifndef CONFIG_HOTPLUG_CPU
 	init_cpu_present(cpu_possible_mask);
 #endif
+	cpumask_copy(&cpu_coherent_mask, cpu_possible_mask);
 }
 
 /* preload SMP state for boot cpu */