arch: arm64: Use _arch_switch() API

Switch to the _arch_switch() API that is required for an SMP-aware
scheduler instead of using the old arch_swap mechanism.

SMP is not supported yet but this is a necessary step in that direction.

Signed-off-by: Carlo Caione <ccaione@baylibre.com>

arch/arm/core/aarch64/CMakeLists.txt

@@ -14,8 +14,7 @@ zephyr_library_sources(
   irq_manage.c
   prep_c.c
   reset.S
-  swap.c
-  swap_helper.S
+  switch.S
   thread.c
   vector_table.S
 )

arch/arm/core/aarch64/Kconfig

@@ -7,6 +7,8 @@ config CPU_CORTEX_A
 	bool
 	select CPU_CORTEX
 	select HAS_FLASH_LOAD_OFFSET
+	select USE_SWITCH
+	select USE_SWITCH_SUPPORTED
 	help
 	  This option signifies the use of a CPU of the Cortex-A family.
 

arch/arm/core/aarch64/isr_wrapper.S

@@ -88,10 +88,24 @@ SECTION_FUNC(TEXT, _isr_wrapper)
 	cmp	x1, #0
 	bne	exit
 
-	/* Check if we need to context switch */
-	ldr	x1, [x0, #_kernel_offset_to_current]
-	ldr	x2, [x0, #_kernel_offset_to_ready_q_cache]
-	cmp	x1, x2
+	/*
+	 * z_arch_get_next_switch_handle() is returning:
+	 *
+	 * - The next thread to schedule in x0
+	 * - The current thread in x1. This value is returned using the
+	 *   **old_thread parameter, so we need to make space on the stack for
+	 *   that.
+	 */
+	stp	x1, xzr, [sp, #-16]!
+	mov	x0, sp
+	bl	z_arch_get_next_switch_handle
+	ldp	x1, xzr, [sp], #16
+
+	/*
+	 * x0: 1st thread in the ready queue
+	 * x1: _current thread
+	 */
+	cmp	x0, x1
 	beq	exit
 
 	/* Switch thread */

arch/arm/core/aarch64/swap.c

@@ -1,23 +0,0 @@
-/*
- * Copyright (c) 2019 Carlo Caione <ccaione@baylibre.com>
- *
- * SPDX-License-Identifier: Apache-2.0
- */
-
-#include <kernel.h>
-#include <kernel_internal.h>
-
-extern const int _k_neg_eagain;
-
-int arch_swap(unsigned int key)
-{
-	_current->arch.swap_return_value = _k_neg_eagain;
-
-	z_arm64_call_svc();
-	irq_unlock(key);
-
-	/* Context switch is performed here. Returning implies the
-	 * thread has been context-switched-in again.
-	 */
-	return _current->arch.swap_return_value;
-}

arch/arm/core/aarch64/switch.S

@@ -22,7 +22,6 @@
 _ASM_FILE_PROLOGUE
 
 GDATA(_kernel)
-GDATA(_k_neg_eagain)
 
 /**
  * @brief Routine to handle context switches
@@ -34,13 +33,12 @@ GDATA(_k_neg_eagain)
 GTEXT(z_arm64_context_switch)
 SECTION_FUNC(TEXT, z_arm64_context_switch)
 #ifdef CONFIG_TRACING
+	stp	x0, x1, [sp, #-16]!
 	stp	xzr, x30, [sp, #-16]!
 	bl	sys_trace_thread_switched_out
 	ldp	xzr, x30, [sp], #16
+	ldp	x0, x1, [sp], #16
 #endif
-	/* load _kernel into x0 and current k_thread into x1 */
-	ldr	x0, =_kernel
-	ldr	x1, [x0, #_kernel_offset_to_current]
 
 	/* addr of callee-saved regs in thread in x2 */
 	ldr	x2, =_thread_offset_to_callee_saved
@@ -58,13 +56,9 @@ SECTION_FUNC(TEXT, z_arm64_context_switch)
 	mov	x1, sp
 	str	x1, [x2]
 
-	/* fetch the thread to run from the ready queue cache */
-	ldr	x1, [x0, #_kernel_offset_to_ready_q_cache]
-	str	x1, [x0, #_kernel_offset_to_current]
-
 	/* addr of callee-saved regs in thread in x2 */
 	ldr	x2, =_thread_offset_to_callee_saved
-	add	x2, x2, x1
+	add	x2, x2, x0
 
 	/* Restore x19-x29 plus x30 */
 	ldp	x19, x20, [x2], #16
@@ -152,7 +146,7 @@ SECTION_FUNC(TEXT, z_thread_entry_wrapper)
 
 GTEXT(z_arm64_svc)
 SECTION_FUNC(TEXT, z_arm64_svc)
-	z_arm64_enter_exc x0, x1, x2
+	z_arm64_enter_exc x2, x3, x4
 
 	switch_el x1, 3f, 2f, 1f
 3:
@@ -197,12 +191,15 @@ offload:
 	b	inv
 
 context_switch:
-	/* Check if we need to context switch */
-	ldr	x0, =_kernel
-	ldr	x1, [x0, #_kernel_offset_to_current]
-	ldr	x2, [x0, #_kernel_offset_to_ready_q_cache]
-	cmp	x1, x2
-	beq	exit
+	/*
+	 * Retrieve x0 and x1 from the stack:
+	 *  - x0 = new_thread->switch_handle = switch_to thread
+	 *  - x1 = x1 = &old_thread->switch_handle = current thread
+	 */
+	ldp	x0, x1, [sp, #(16 * 10)]
+
+	/* Get old thread from x1 */
+	sub	x1, x1, ___thread_t_switch_handle_OFFSET
 
 	/* Switch thread */
 	bl	z_arm64_context_switch

arch/arm/core/aarch64/thread.c

@@ -77,4 +77,13 @@ void arch_new_thread(struct k_thread *thread, k_thread_stack_t *stack,
 
 	thread->callee_saved.sp = (uint64_t)pInitCtx;
 	thread->callee_saved.x30 = (uint64_t)z_thread_entry_wrapper;
+
+	thread->switch_handle = thread;
+}
+
+void *z_arch_get_next_switch_handle(struct k_thread **old_thread)
+{
+	*old_thread =  _current;
+
+	return z_get_next_switch_handle(*old_thread);
 }

arch/arm/core/offsets/offsets_aarch64.c

@@ -29,6 +29,4 @@
 #include <kernel_arch_data.h>
 #include <kernel_offsets.h>
 
-GEN_OFFSET_SYM(_thread_arch_t, swap_return_value);
-
 #endif /* _ARM_OFFSETS_INC_ */

arch/arm/include/aarch64/exc.h

@@ -38,7 +38,7 @@ static ALWAYS_INLINE bool arch_is_in_isr(void)
 }
 
 
-extern void z_arm64_call_svc(void);
+extern void z_arm64_call_svc(void *switch_to, void **switched_from);
 
 #ifdef __cplusplus
 }

arch/arm/include/aarch64/kernel_arch_func.h

@@ -32,10 +32,11 @@ static ALWAYS_INLINE void arch_kernel_init(void)
 {
 }
 
-static ALWAYS_INLINE void
-arch_thread_return_value_set(struct k_thread *thread, unsigned int value)
+static inline void arch_switch(void *switch_to, void **switched_from)
 {
-	thread->arch.swap_return_value = value;
+	z_arm64_call_svc(switch_to, switched_from);
+
+	return;
 }
 
 extern void z_arm64_fatal_error(const z_arch_esf_t *esf, unsigned int reason);

arch/arm/include/aarch64/offsets_short_arch.h

@@ -9,7 +9,4 @@
 
 #include <offsets.h>
 
-#define _thread_offset_to_swap_return_value \
-	(___thread_t_arch_OFFSET + ___thread_arch_t_swap_return_value_OFFSET)
-
 #endif /* ZEPHYR_ARCH_ARM_INCLUDE_AARCH64_OFFSETS_SHORT_ARCH_H_ */

include/arch/arm/aarch64/thread.h

@@ -41,7 +41,7 @@ struct _callee_saved {
 typedef struct _callee_saved _callee_saved_t;
 
 struct _thread_arch {
-	uint32_t swap_return_value;
+	/* empty */
 };
 
 typedef struct _thread_arch _thread_arch_t;