mpfs_entrypoints.c: Add simple ACK mechanism for CPU boot

CPUs will acknowledge that they have booted, the primary CPU handling the
boot can then wait for others to complete their boot, before booting
itself.

arch/risc-v/src/mpfs/mpfs_entrypoints.c

@@ -29,6 +29,7 @@
 #include <stdint.h>
 #include <stdbool.h>
 
+#include <nuttx/atomic.h>
 #include <nuttx/compiler.h>
 
 #include <sys/types.h>
@@ -90,6 +91,8 @@ uint8_t g_mpfs_boot_stacks[ENTRY_STACK * ENTRYPT_CNT]
   aligned_data(STACK_ALIGNMENT);
 #endif
 
+static int g_cpus_booted;
+
 /****************************************************************************
  * Public Functions
  ****************************************************************************/
@@ -128,6 +131,9 @@ void mpfs_jump_to_app(void)
       "la   t0, g_app_entrypoints\n"         /* Entrypoint table base */
       "add  t0, t0, t1\n"                    /* Index in table */
       "ld   t0, 0(t0)\n"                     /* Load the address from table */
+      "li   t1, 1\n"
+      "la   t2, g_cpus_booted\n"
+      "amoadd.w.aqrl zero, t1, 0(t2)\n"      /* g_cpus_booted + 1 */
       "jr   t0\n"                            /* Jump to entrypoint */
       :
 #ifdef CONFIG_MPFS_BOARD_PMP
@@ -246,4 +252,23 @@ bool mpfs_get_use_sbi(uint64_t hartid)
   return false;
 }
 
+/****************************************************************************
+ * Name: mpfs_cpus_booted
+ *
+ * Description:
+ *   Get amount of CPUs that have completed boot.
+ *
+ * Input Parameters:
+ *   None.
+ *
+ * Returned value:
+ *   Amount of CPUs that have booted.
+ *
+ ****************************************************************************/
+
+int mpfs_cpus_booted(void)
+{
+  return atomic_load(&g_cpus_booted);
+}
+
 #endif /* CONFIG_MPFS_BOOTLOADER */

arch/risc-v/src/mpfs/mpfs_entrypoints.h

@@ -102,6 +102,22 @@ int mpfs_set_use_sbi(uint64_t hartid, bool use_sbi);
 
 bool mpfs_get_use_sbi(uint64_t hartid);
 
+/****************************************************************************
+ * Name: mpfs_cpus_booted
+ *
+ * Description:
+ *   Get amount of CPUs that have completed boot.
+ *
+ * Input Parameters:
+ *   None.
+ *
+ * Returned value:
+ *   Amount of CPUs that have booted.
+ *
+ ****************************************************************************/
+
+int mpfs_cpus_booted(void);
+
 #if defined(__cplusplus)
 }
 #endif