From bec9676493c51a454541e885ad33030e58d9d257 Mon Sep 17 00:00:00 2001
From: HiFiPhile <admin@hifiphile.com>
Date: Sun, 15 Jun 2025 12:02:15 +0200
Subject: [PATCH 1/2] osal/none: add nested count to spin lock

Signed-off-by: HiFiPhile <admin@hifiphile.com>
---
 src/osal/osal_none.h | 26 +++++++++++++++++++++++---
 1 file changed, 23 insertions(+), 3 deletions(-)

diff --git a/src/osal/osal_none.h b/src/osal/osal_none.h
index bc86dcb28..d9890efbc 100644
--- a/src/osal/osal_none.h
+++ b/src/osal/osal_none.h
@@ -34,26 +34,46 @@ extern "C" {
 //--------------------------------------------------------------------+
 // Spinlock API
 //--------------------------------------------------------------------+
+// Note: This implementation is designed for bare-metal single-core systems without RTOS.
+// - Supports nested locking within the same execution context
+// - NOT suitable for true SMP (Symmetric Multi-Processing) systems
+// - NOT thread-safe for multi-threaded environments
+// - Primarily manages interrupt enable/disable state for critical sections
 typedef struct {
   void (* interrupt_set)(bool enabled);
+  uint32_t nested_count;
 } osal_spinlock_t;
 
 // For SMP, spinlock must be locked by hardware, cannot just use interrupt
 #define OSAL_SPINLOCK_DEF(_name, _int_set) \
-  osal_spinlock_t _name = { .interrupt_set = _int_set }
+  osal_spinlock_t _name = { .interrupt_set = _int_set, .nested_count = 0 }
 
 TU_ATTR_ALWAYS_INLINE static inline void osal_spin_init(osal_spinlock_t *ctx) {
   (void) ctx;
 }
 
 TU_ATTR_ALWAYS_INLINE static inline void osal_spin_lock(osal_spinlock_t *ctx, bool in_isr) {
-  if (!in_isr) {
+  // Disable interrupts first to make nested_count increment atomic
+  if (!in_isr && ctx->nested_count == 0) {
     ctx->interrupt_set(false);
   }
+  ctx->nested_count++;
 }
 
 TU_ATTR_ALWAYS_INLINE static inline void osal_spin_unlock(osal_spinlock_t *ctx, bool in_isr) {
-  if (!in_isr) {
+  // Check for underflow - unlock without lock
+  if (ctx->nested_count == 0) {
+    // Re-enable interrupts before asserting to avoid leaving interrupts disabled
+    if (!in_isr) {
+      ctx->interrupt_set(true);
+    }
+    TU_ASSERT(0,);
+  }
+
+  ctx->nested_count--;
+
+  // Only re-enable interrupts when fully unlocked
+  if (!in_isr && ctx->nested_count == 0) {
     ctx->interrupt_set(true);
   }
 }

From 650c4b061c45c20d3d059f1c5ce6013b700ce1f1 Mon Sep 17 00:00:00 2001
From: hathach <thach@tinyusb.org>
Date: Wed, 19 Nov 2025 17:06:19 +0700
Subject: [PATCH 2/2] return if spin is underflow

---
 src/osal/osal_none.h | 7 +------
 1 file changed, 1 insertion(+), 6 deletions(-)

diff --git a/src/osal/osal_none.h b/src/osal/osal_none.h
index d9890efbc..174136e38 100644
--- a/src/osal/osal_none.h
+++ b/src/osal/osal_none.h
@@ -61,13 +61,8 @@ TU_ATTR_ALWAYS_INLINE static inline void osal_spin_lock(osal_spinlock_t *ctx, bo
 }
 
 TU_ATTR_ALWAYS_INLINE static inline void osal_spin_unlock(osal_spinlock_t *ctx, bool in_isr) {
-  // Check for underflow - unlock without lock
   if (ctx->nested_count == 0) {
-    // Re-enable interrupts before asserting to avoid leaving interrupts disabled
-    if (!in_isr) {
-      ctx->interrupt_set(true);
-    }
-    TU_ASSERT(0,);
+    return; // spin is not locked to begin with
   }
 
   ctx->nested_count--;