From a6cb8b06dbdd20b96a884c2bf957f9da1e53ab32 Mon Sep 17 00:00:00 2001
From: Ioannis Glaropoulos <Ioannis.Glaropoulos@nordicsemi.no>
Date: Thu, 9 May 2019 21:55:10 +0200
Subject: [PATCH] kernel: introduce k_float_disable system call

We introduce k_float_disable() system call, to allow threads to
disable floating point context preservation. The system call is
to be used in FP Sharing Registers mode (CONFIG_FP_SHARING=y).

Signed-off-by: Ioannis Glaropoulos <Ioannis.Glaropoulos@nordicsemi.no>
---
 include/kernel.h                 | 23 +++++++++++++++++++++++
 kernel/include/kernel_internal.h | 18 ++++++++++++++++++
 kernel/thread.c                  | 20 ++++++++++++++++++++
 3 files changed, 61 insertions(+)

diff --git a/include/kernel.h b/include/kernel.h
index 3f70f6e2145..529cc58594a 100644
--- a/include/kernel.h
+++ b/include/kernel.h
@@ -4906,6 +4906,29 @@ __syscall void k_str_out(char *c, size_t n);
 extern void z_arch_start_cpu(int cpu_num, k_thread_stack_t *stack, int sz,
 			    void (*fn)(int key, void *data), void *arg);
 
+
+/**
+ * @brief Disable preservation of floating point context information.
+ *
+ * This routine informs the kernel that the specified thread
+ * will no longer be using the floating point registers.
+ *
+ * @warning
+ * Some architectures apply restrictions on how the disabling of floating
+ * point preservation may be requested, see z_arch_float_disable.
+ *
+ * @warning
+ * This routine should only be used to disable floating point support for
+ * a thread that currently has such support enabled.
+ *
+ * @param thread ID of thread.
+ *
+ * @retval 0       On success.
+ * @retval -ENOSYS If the floating point disabling is not implemented.
+ *         -EINVAL If the floating point disabling could not be performed.
+ */
+__syscall int k_float_disable(struct k_thread *thread);
+
 #ifdef __cplusplus
 }
 #endif
diff --git a/kernel/include/kernel_internal.h b/kernel/include/kernel_internal.h
index dfc1c1fa33e..efe708dea49 100644
--- a/kernel/include/kernel_internal.h
+++ b/kernel/include/kernel_internal.h
@@ -51,6 +51,24 @@ extern void z_setup_new_thread(struct k_thread *new_thread,
 			      void *p1, void *p2, void *p3,
 			      int prio, u32_t options, const char *name);
 
+#if defined(CONFIG_FLOAT) && defined(CONFIG_FP_SHARING)
+/**
+ * @brief Disable floating point context preservation
+ *
+ * The function is used to disable the preservation of floating
+ * point context information for a particular thread.
+ *
+ * @note
+ * For ARM architecture, disabling floating point preservation
+ * - may only be requested for the current thread
+ * - cannot be requested in ISRs.
+ *
+ * @retval 0       On success.
+ * @retval -EINVAL If the floating point disabling could not be performed.
+ */
+extern int z_arch_float_disable(struct k_thread *thread);
+#endif /* CONFIG_FLOAT && CONFIG_FP_SHARING */
+
 #ifdef CONFIG_USERSPACE
 /**
  * @brief Get the maximum number of partitions for a memory domain
diff --git a/kernel/thread.c b/kernel/thread.c
index de40fa7c804..b2494a48a64 100644
--- a/kernel/thread.c
+++ b/kernel/thread.c
@@ -727,4 +727,24 @@ void z_spin_lock_set_owner(struct k_spinlock *l)
 	l->thread_cpu = _current_cpu->id | (uintptr_t)_current;
 }
 
+int z_impl_k_float_disable(struct k_thread *thread)
+{
+#if defined(CONFIG_FLOAT) && defined(CONFIG_FP_SHARING)
+	return z_arch_float_disable(thread);
+#else
+	return -ENOSYS;
+#endif /* CONFIG_FLOAT && CONFIG_FP_SHARING */
+}
+
+#ifdef CONFIG_USERSPACE
+Z_SYSCALL_HANDLER(k_float_disable, thread_p)
+{
+	struct k_thread *thread = (struct k_thread *)thread_p;
+
+	Z_OOPS(Z_SYSCALL_OBJ(thread, K_OBJ_THREAD));
+
+	return z_impl_k_float_disable((struct k_thread *)thread_p);
+}
+#endif /* CONFIG_USERSPACE */
+
 #endif