RISC-V: Add logical CPU indexing for RISC-V

Currently, both Linux CPU id and hart id are same.
This is not recommended as it will lead to discontinuous CPU
indexing in Linux. Moreover, kdump kernel will run from CPU0
which would be absent if we follow existing scheme.

Implement a logical mapping between Linux CPU id and hart
id to decouple these two. Always mark the boot processor as
CPU0 and all other CPUs get the logical CPU id based on their
booting order.

Signed-off-by: Atish Patra <atish.patra@wdc.com>
Reviewed-by: Anup Patel <anup@brainfault.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Palmer Dabbelt <palmer@sifive.com>

arch/riscv/kernel/setup.c

@@ -82,6 +82,10 @@ EXPORT_SYMBOL(empty_zero_page);
 /* The lucky hart to first increment this variable will boot the other cores */
 atomic_t hart_lottery;
 
+unsigned long __cpuid_to_hartid_map[NR_CPUS] = {
+	[0 ... NR_CPUS-1] = INVALID_HARTID
+};
+
 #ifdef CONFIG_BLK_DEV_INITRD
 static void __init setup_initrd(void)
 {

arch/riscv/kernel/smp.c

@@ -38,7 +38,26 @@ enum ipi_message_type {
 	IPI_MAX
 };
 
+int riscv_hartid_to_cpuid(int hartid)
+{
+	int i = -1;
 
+	for (i = 0; i < NR_CPUS; i++)
+		if (cpuid_to_hartid_map(i) == hartid)
+			return i;
+
+	pr_err("Couldn't find cpu id for hartid [%d]\n", hartid);
+	BUG();
+	return i;
+}
+
+void riscv_cpuid_to_hartid_mask(const struct cpumask *in, struct cpumask *out)
+{
+	int cpu;
+
+	for_each_cpu(cpu, in)
+		cpumask_set_cpu(cpuid_to_hartid_map(cpu), out);
+}
 /* Unsupported */
 int setup_profiling_timer(unsigned int multiplier)
 {