arch: xtensa: Carve space for saved HiFi regs

As the BSA can not be used when lazy HiFi context switching is
used, a more permanent and predictable location in which to store
the registers is required. To this end ...
  1. reserve some space in the arch-specific portion of the k_thread
     structure for those registers.
  2. clear that region when the thread is created.

Signed-off-by: Peter Mitsis <[email protected]>

Author: peter-mitsis

arch/xtensa/core/thread.c

@@ -120,6 +120,10 @@ void arch_new_thread(struct k_thread *thread, k_thread_stack_t *stack,
 {
 	thread->switch_handle = init_stack(thread, (int *)stack_ptr, entry,
 					   p1, p2, p3);
+#ifdef CONFIG_XTENSA_LAZY_HIFI_SHARING
+	memset(thread->arch.hifi_regs, 0, sizeof(thread->arch.hifi_regs));
+#endif /* CONFIG_XTENSA_LAZY_HIFI_SHARING */
+
 #ifdef CONFIG_KERNEL_COHERENCE
 	__ASSERT((((size_t)stack) % XCHAL_DCACHE_LINESIZE) == 0, "");
 	__ASSERT((((size_t)stack_ptr) % XCHAL_DCACHE_LINESIZE) == 0, "");

include/zephyr/arch/xtensa/thread.h

@@ -14,6 +14,10 @@
 #include <zephyr/arch/xtensa/mpu.h>
 #endif
 
+#ifdef CONFIG_XTENSA_LAZY_HIFI_SHARING
+#include <xtensa/config/tie.h>
+#endif
+
 /* Xtensa doesn't use these structs, but Zephyr core requires they be
  * defined so they can be included in struct _thread_base.  Dummy
  * field exists for sizeof compatibility with C++.
@@ -48,6 +52,11 @@ struct _thread_arch {
 	 */
 	uint32_t return_ps;
 #endif
+
+#ifdef CONFIG_XTENSA_LAZY_HIFI_SHARING
+	/* A non-BSA region is required for lazy save/restore */
+	uint8_t hifi_regs[XCHAL_CP1_SA_SIZE] __aligned(XCHAL_CP1_SA_ALIGN);
+#endif
 };
 
 typedef struct _thread_arch _thread_arch_t;