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Subject[PATCH 5/8] RISC-V: implement low-level interrupt handling
Date
Add support for a routine that dispatches exceptions with the interrupt
flags set to either the IPI or irqdomain code (and the clock source in the
future).

Loosely based on the irq-riscv-int.c irqchip driver from the RISC-V tree.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
arch/riscv/kernel/entry.S | 4 +--
arch/riscv/kernel/irq.c | 52 ++++++++++++++++++++++++++++++++-------
2 files changed, 45 insertions(+), 11 deletions(-)

diff --git a/arch/riscv/kernel/entry.S b/arch/riscv/kernel/entry.S
index 9aaf6c986771..fa2c08e3c05e 100644
--- a/arch/riscv/kernel/entry.S
+++ b/arch/riscv/kernel/entry.S
@@ -168,8 +168,8 @@ ENTRY(handle_exception)

/* 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
diff --git a/arch/riscv/kernel/irq.c b/arch/riscv/kernel/irq.c
index 7bcdaed15703..ab5f3e22c7cc 100644
--- a/arch/riscv/kernel/irq.c
+++ b/arch/riscv/kernel/irq.c
@@ -1,21 +1,55 @@
+// 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();
--
2.18.0
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