From ea85010a633c4c9f015e4d6fd9816fd26d4006f1 Mon Sep 17 00:00:00 2001
From: Ivan Velickovic <i.velickovic@unsw.edu.au>
Date: Fri, 27 Mar 2026 15:15:22 +1100
Subject: [PATCH] loader: handle non-PSCI ARM platforms better

This makes things slightly better, main thing is that we make sure
we don't try boot secondary CPUs via PSCI if it's unavailable.

Signed-off-by: Ivan Velickovic <i.velickovic@unsw.edu.au>
---
 loader/src/aarch64/cpus.c | 5 ++++-
 loader/src/aarch64/init.c | 4 ++--
 loader/src/cpus.h         | 5 +++++
 3 files changed, 11 insertions(+), 3 deletions(-)

diff --git a/loader/src/aarch64/cpus.c b/loader/src/aarch64/cpus.c
index bf3d81094..130000248 100644
--- a/loader/src/aarch64/cpus.c
+++ b/loader/src/aarch64/cpus.c
@@ -189,7 +189,7 @@ int plat_start_cpu(int logical_cpu)
     while (__atomic_load_n(&arm_spin_table_secondary_cpu_data, __ATOMIC_ACQUIRE) != 0);
     arm_spin_table_cpu_start(logical_cpu, (uint64_t)sp);
     return 0;
-#else
+#elif !defined(ARM_PSCI_UNAVAILABLE)
     uint64_t ret = arm_smc64_call(
                        PSCI_FUNCTION_CPU_ON,
                        /* target_cpu */ psci_target_cpus[logical_cpu],
@@ -204,5 +204,8 @@ int plat_start_cpu(int logical_cpu)
     }
 
     return ret;
+#else
+    LDR_PRINT("ERROR", 0, "unknown CPU start method for this platform");
+    return -1;
 #endif
 }
diff --git a/loader/src/aarch64/init.c b/loader/src/aarch64/init.c
index 7eafef432..2d8f2e0cd 100644
--- a/loader/src/aarch64/init.c
+++ b/loader/src/aarch64/init.c
@@ -8,6 +8,7 @@
 #include "../arch.h"
 #include "../loader.h"
 #include "../uart.h"
+#include "../cpus.h"
 #include "el.h"
 #include "smc.h"
 
@@ -105,8 +106,7 @@ void arch_init(void)
         fail();
     }
 
-    // TODO: handle non-PSCI platforms better, see https://github.com/seL4/microkit/issues/401.
-#if !defined(CONFIG_PLAT_BCM2711) && !defined(BOARD_kria_k26)
+#if !defined(ARM_PSCI_UNAVAILABLE)
     uint32_t ret = arm_smc32_call(PSCI_FUNCTION_VERSION, /* unused */ 0, 0, 0);
     /* the return value has no error codes, but if we get it wrong this is what we will get */
     if (ret == PSCI_RETURN_NOT_SUPPORTED) {
diff --git a/loader/src/cpus.h b/loader/src/cpus.h
index a94f221ec..d01f888e2 100644
--- a/loader/src/cpus.h
+++ b/loader/src/cpus.h
@@ -11,6 +11,11 @@
 
 #include <kernel/gen_config.h>
 
+#if defined(CONFIG_PLAT_BCM2711) || defined(BOARD_kria_k26)
+/* There are a couple of cases where we cannot rely on having ARM PSCI available. */
+#define ARM_PSCI_UNAVAILABLE
+#endif
+
 /* Define our own variant of the seL4 config */
 #define NUM_ACTIVE_CPUS CONFIG_MAX_NUM_NODES