riscv: Support irq_work via self IPIs

Support for arch_irq_work_raise() and arch_irq_work_has_interrupt() was
missing from riscv (a prerequisite for FULL_NOHZ).
Signed-off-by: Greentime Hu <greentime.hu@sifive.com>
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>

arch/riscv/include/asm/irq_work.h

+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_RISCV_IRQ_WORK_H
+#define _ASM_RISCV_IRQ_WORK_H
+
+static inline bool arch_irq_work_has_interrupt(void)
+{
+	return true;
+}
+extern void arch_irq_work_raise(void);
+#endif /* _ASM_RISCV_IRQ_WORK_H */

arch/riscv/kernel/smp.c

@@ -16,6 +16,7 @@
 #include <linux/sched.h>
 #include <linux/seq_file.h>
 #include <linux/delay.h>
+#include <linux/irq_work.h>
 
 #include <asm/clint.h>
 #include <asm/sbi.h>
@@ -26,6 +27,7 @@ enum ipi_message_type {
 	IPI_RESCHEDULE,
 	IPI_CALL_FUNC,
 	IPI_CPU_STOP,
+	IPI_IRQ_WORK,
 	IPI_MAX
 };
 
@@ -123,6 +125,13 @@ static inline void clear_ipi(void)
 		clint_clear_ipi(cpuid_to_hartid_map(smp_processor_id()));
 }
 
+#ifdef CONFIG_IRQ_WORK
+void arch_irq_work_raise(void)
+{
+	send_ipi_single(smp_processor_id(), IPI_IRQ_WORK);
+}
+#endif
+
 void handle_IPI(struct pt_regs *regs)
 {
 	struct pt_regs *old_regs = set_irq_regs(regs);
@@ -158,6 +167,11 @@ void handle_IPI(struct pt_regs *regs)
 			ipi_stop();
 		}
 
+		if (ops & (1 << IPI_IRQ_WORK)) {
+			stats[IPI_IRQ_WORK]++;
+			irq_work_run();
+		}
+
 		BUG_ON((ops >> IPI_MAX) != 0);
 
 		/* Order data access and bit testing. */
@@ -173,6 +187,7 @@ static const char * const ipi_names[] = {
 	[IPI_RESCHEDULE]	= "Rescheduling interrupts",
 	[IPI_CALL_FUNC]		= "Function call interrupts",
 	[IPI_CPU_STOP]		= "CPU stop interrupts",
+	[IPI_IRQ_WORK]		= "IRQ work interrupts",
 };
 
 void show_ipi_stats(struct seq_file *p, int prec)