arch/riscv/core/thread.c

/*
 * Copyright (c) 2016 Jean-Paul Etienne <fractalclone@gmail.com>
 *
 * SPDX-License-Identifier: Apache-2.0
 */

#include <kernel.h>
#include <ksched.h>

void z_thread_entry_wrapper(k_thread_entry_t thread,
			    void *arg1,
			    void *arg2,
			    void *arg3);

void arch_new_thread(struct k_thread *thread, k_thread_stack_t *stack,
		     char *stack_ptr, k_thread_entry_t entry,
		     void *p1, void *p2, void *p3)
{
	struct __esf *stack_init;

#ifdef CONFIG_RISCV_SOC_CONTEXT_SAVE
	const struct soc_esf soc_esf_init = {SOC_ESF_INIT};
#endif

	/* Initial stack frame for thread */
	stack_init = Z_STACK_PTR_TO_FRAME(struct __esf, stack_ptr);

	/* Setup the initial stack frame */
	stack_init->a0 = (ulong_t)entry;
	stack_init->a1 = (ulong_t)p1;
	stack_init->a2 = (ulong_t)p2;
	stack_init->a3 = (ulong_t)p3;
	/*
	 * Following the RISC-V architecture,
	 * the MSTATUS register (used to globally enable/disable interrupt),
	 * as well as the MEPC register (used to by the core to save the
	 * value of the program counter at which an interrupt/exception occcurs)
	 * need to be saved on the stack, upon an interrupt/exception
	 * and restored prior to returning from the interrupt/exception.
	 * This shall allow to handle nested interrupts.
	 *
	 * Given that context switching is performed via a system call exception
	 * within the RISCV architecture implementation, initially set:
	 * 1) MSTATUS to MSTATUS_DEF_RESTORE in the thread stack to enable
	 *    interrupts when the newly created thread will be scheduled;
	 * 2) MEPC to the address of the z_thread_entry_wrapper in the thread
	 *    stack.
	 * Hence, when going out of an interrupt/exception/context-switch,
	 * after scheduling the newly created thread:
	 * 1) interrupts will be enabled, as the MSTATUS register will be
	 *    restored following the MSTATUS value set within the thread stack;
	 * 2) the core will jump to z_thread_entry_wrapper, as the program
	 *    counter will be restored following the MEPC value set within the
	 *    thread stack.
	 */
	stack_init->mstatus = MSTATUS_DEF_RESTORE;
#if defined(CONFIG_FPU) && defined(CONFIG_FPU_SHARING)
	if ((thread->base.user_options & K_FP_REGS) != 0) {
		stack_init->mstatus |= MSTATUS_FS_INIT;
	}
	stack_init->fp_state = 0;
#endif
	stack_init->mepc = (ulong_t)z_thread_entry_wrapper;

#ifdef CONFIG_RISCV_SOC_CONTEXT_SAVE
	stack_init->soc_context = soc_esf_init;
#endif

	thread->callee_saved.sp = (ulong_t)stack_init;
}

#if defined(CONFIG_FPU) && defined(CONFIG_FPU_SHARING)
int arch_float_disable(struct k_thread *thread)
{
	unsigned int key;

	if (thread != _current) {
		return -EINVAL;
	}

	if (arch_is_in_isr()) {
		return -EINVAL;
	}

	/* Ensure a preemptive context switch does not occur */
	key = irq_lock();

	/* Disable all floating point capabilities for the thread */
	thread->base.user_options &= ~K_FP_REGS;

	/* Clear the FS bits to disable the FPU. */
	__asm__ volatile (
		"mv t0, %0\n"
		"csrrc x0, mstatus, t0\n"
		:
		: "r" (MSTATUS_FS_MASK)
		);

	irq_unlock(key);

	return 0;
}


int arch_float_enable(struct k_thread *thread)
{
	unsigned int key;

	if (thread != _current) {
		return -EINVAL;
	}

	if (arch_is_in_isr()) {
		return -EINVAL;
	}

	/* Ensure a preemptive context switch does not occur */
	key = irq_lock();

	/* Enable all floating point capabilities for the thread. */
	thread->base.user_options |= K_FP_REGS;

	/* Set the FS bits to Initial to enable the FPU. */
	__asm__ volatile (
		"mv t0, %0\n"
		"csrrs x0, mstatus, t0\n"
		:
		: "r" (MSTATUS_FS_INIT)
		);

	irq_unlock(key);

	return 0;
}
#endif /* CONFIG_FPU && CONFIG_FPU_SHARING */