RISC-V: implement low-level interrupt handling

	/* Handle interrupts */

	move a0, sp /* pt_regs */

	REG_L a1, handle_arch_irq

	jr a1

	move a1, s4 /* scause */

	tail do_IRQ

1:

	/* Exceptions run with interrupts enabled */

	csrs sstatus, SR_SIE

// SPDX-License-Identifier: GPL-2.0

/*

 * Copyright (C) 2012 Regents of the University of California

 * Copyright (C) 2017 SiFive

 *

 *   This program is free software; you can redistribute it and/or

 *   modify it under the terms of the GNU General Public License

 *   as published by the Free Software Foundation, version 2.

 *

 *   This program is distributed in the hope that it will be useful,

 *   but WITHOUT ANY WARRANTY; without even the implied warranty of

 *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

 *   GNU General Public License for more details.

 * Copyright (C) 2018 Christoph Hellwig

 */

#include <linux/interrupt.h>

#include <linux/irqchip.h>

#include <linux/irqdomain.h>

/*

 * Possible interrupt causes:

 */

#define INTERRUPT_CAUSE_SOFTWARE    1

#define INTERRUPT_CAUSE_TIMER       5

#define INTERRUPT_CAUSE_EXTERNAL    9

/*

 * The high order bit of the trap cause register is always set for

 * interrupts, which allows us to differentiate them from exceptions

 * quickly.  The INTERRUPT_CAUSE_* macros don't contain that bit, so we

 * need to mask it off.

 */

#define INTERRUPT_CAUSE_FLAG	(1UL << (__riscv_xlen - 1))

asmlinkage void __irq_entry do_IRQ(struct pt_regs *regs, unsigned long cause)

{

	struct pt_regs *old_regs = set_irq_regs(regs);

	irq_enter();

	switch (cause & ~INTERRUPT_CAUSE_FLAG) {

#ifdef CONFIG_SMP

	case INTERRUPT_CAUSE_SOFTWARE:

		/*

		 * We only use software interrupts to pass IPIs, so if a non-SMP

		 * system gets one, then we don't know what to do.

		 */

		riscv_software_interrupt();

		break;

#endif

	case INTERRUPT_CAUSE_EXTERNAL:

		handle_arch_irq(regs);

		break;

	default:

		panic("unexpected interrupt cause");

	}

	irq_exit();

	set_irq_regs(old_regs);

}

void __init init_IRQ(void)

{

	irqchip_init();