riscv: sifive_u: Set the minimum number of cpus to 2

It is not useful if we only have one management CPU.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
[Palmer: Set default CPUs to 2]
Reviewed-by: Palmer Dabbelt <palmer@sifive.com>
Signed-off-by: Palmer Dabbelt <palmer@sifive.com>

hw/riscv/sifive_u.c

@@ -10,7 +10,8 @@
  * 1) CLINT (Core Level Interruptor)
  * 2) PLIC (Platform Level Interrupt Controller)
  *
- * This board currently uses a hardcoded devicetree that indicates one hart.
+ * This board currently generates devicetree dynamically that indicates at least
+ * two harts.
  *
  * This program is free software; you can redistribute it and/or modify it
  * under the terms and conditions of the GNU General Public License,
@@ -433,6 +434,8 @@ static void riscv_sifive_u_machine_init(MachineClass *mc)
      * management CPU.
      */
     mc->max_cpus = 4;
+    mc->min_cpus = SIFIVE_U_MANAGEMENT_CPU_COUNT + 1;
+    mc->default_cpus = mc->min_cpus;
 }
 
 DEFINE_MACHINE("sifive_u", riscv_sifive_u_machine_init)

include/hw/riscv/sifive_u.h

@@ -69,6 +69,8 @@ enum {
     SIFIVE_U_GEM_CLOCK_FREQ = 125000000
 };
 
+#define SIFIVE_U_MANAGEMENT_CPU_COUNT   1
+
 #define SIFIVE_U_PLIC_HART_CONFIG "MS"
 #define SIFIVE_U_PLIC_NUM_SOURCES 54
 #define SIFIVE_U_PLIC_NUM_PRIORITIES 7