RISC-V: self-contained IPI handling routine

Currently, the IPI handling routine riscv_software_interrupt() does
not take any argument and also does not perform irq_enter()/irq_exit().

This patch makes IPI handling routine more self-contained by:
1. Passing "pt_regs *" argument
2. Explicitly doing irq_enter()/irq_exit()
3. Explicitly save/restore "pt_regs *" using set_irq_regs()

With above changes, IPI handling routine does not depend on caller
function to perform irq_enter()/irq_exit() and save/restore of
"pt_regs *" hence its more self-contained. This also enables us
to call IPI handling routine from IRQCHIP drivers.
Signed-off-by: NAnup Patel <anup.patel@wdc.com>
Reviewed-by: NAtish Patra <atish.patra@wdc.com>
Reviewed-by: NPalmer Dabbelt <palmerdabbelt@google.com>
Acked-by: NPalmer Dabbelt <palmerdabbelt@google.com>
Signed-off-by: NPalmer Dabbelt <palmerdabbelt@google.com>

arch/riscv/include/asm/irq.h

@@ -13,7 +13,6 @@
 #define NR_IRQS         0
 
 void riscv_timer_interrupt(void);
-void riscv_software_interrupt(void);
 
 #include <asm-generic/irq.h>
 

arch/riscv/include/asm/smp.h

@@ -28,6 +28,9 @@ void show_ipi_stats(struct seq_file *p, int prec);
 /* SMP initialization hook for setup_arch */
 void __init setup_smp(void);
 
+/* Called from C code, this handles an IPI. */
+void handle_IPI(struct pt_regs *regs);
+
 /* Hook for the generic smp_call_function_many() routine. */
 void arch_send_call_function_ipi_mask(struct cpumask *mask);
 

arch/riscv/kernel/irq.c

@@ -19,12 +19,15 @@ int arch_show_interrupts(struct seq_file *p, int prec)
 
 asmlinkage __visible void __irq_entry do_IRQ(struct pt_regs *regs)
 {
-	struct pt_regs *old_regs = set_irq_regs(regs);
+	struct pt_regs *old_regs;
 
-	irq_enter();
 	switch (regs->cause & ~CAUSE_IRQ_FLAG) {
 	case RV_IRQ_TIMER:
+		old_regs = set_irq_regs(regs);
+		irq_enter();
 		riscv_timer_interrupt();
+		irq_exit();
+		set_irq_regs(old_regs);
 		break;
 #ifdef CONFIG_SMP
 	case RV_IRQ_SOFT:
@@ -32,19 +35,20 @@ asmlinkage __visible void __irq_entry do_IRQ(struct pt_regs *regs)
 		 * 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();
+		handle_IPI(regs);
 		break;
 #endif
 	case RV_IRQ_EXT:
+		old_regs = set_irq_regs(regs);
+		irq_enter();
 		handle_arch_irq(regs);
+		irq_exit();
+		set_irq_regs(old_regs);
 		break;
 	default:
 		pr_alert("unexpected interrupt cause 0x%lx", regs->cause);
 		BUG();
 	}
-	irq_exit();
-
-	set_irq_regs(old_regs);
 }
 
 void __init init_IRQ(void)

arch/riscv/kernel/smp.c

@@ -123,11 +123,14 @@ static inline void clear_ipi(void)
 		clint_clear_ipi(cpuid_to_hartid_map(smp_processor_id()));
 }
 
-void riscv_software_interrupt(void)
+void handle_IPI(struct pt_regs *regs)
 {
+	struct pt_regs *old_regs = set_irq_regs(regs);
 	unsigned long *pending_ipis = &ipi_data[smp_processor_id()].bits;
 	unsigned long *stats = ipi_data[smp_processor_id()].stats;
 
+	irq_enter();
+
 	clear_ipi();
 
 	while (true) {
@@ -138,7 +141,7 @@ void riscv_software_interrupt(void)
 
 		ops = xchg(pending_ipis, 0);
 		if (ops == 0)
-			return;
+			goto done;
 
 		if (ops & (1 << IPI_RESCHEDULE)) {
 			stats[IPI_RESCHEDULE]++;
@@ -160,6 +163,10 @@ void riscv_software_interrupt(void)
 		/* Order data access and bit testing. */
 		mb();
 	}
+
+done:
+	irq_exit();
+	set_irq_regs(old_regs);
 }
 
 static const char * const ipi_names[] = {