[PATCH v3 3/4] clocksource: timer-riscv: Make timer interrupt as a per-CPU interrupt

[Anup Patel]

Instead of directly calling RISC-V timer interrupt handler from
RISC-V local interrupt conntroller driver, this patch implements
RISC-V timer interrupt as a per-CPU interrupt using per-CPU APIs
of Linux IRQ subsystem.

Signed-off-by: Anup Patel <anup.patel@xxxxxxx>
---
 arch/riscv/include/asm/irq.h      |  2 -
 drivers/clocksource/timer-riscv.c | 79 ++++++++++++++++++++-----------
 drivers/irqchip/irq-riscv-intc.c  |  8 ----
 3 files changed, 52 insertions(+), 37 deletions(-)

diff --git a/arch/riscv/include/asm/irq.h b/arch/riscv/include/asm/irq.h
index a9e5f07a7e9c..9807ad164015 100644
--- a/arch/riscv/include/asm/irq.h
+++ b/arch/riscv/include/asm/irq.h
@@ -10,8 +10,6 @@
 #include <linux/interrupt.h>
 #include <linux/linkage.h>
 
-void riscv_timer_interrupt(void);
-
 #include <asm-generic/irq.h>
 
 #endif /* _ASM_RISCV_IRQ_H */
diff --git a/drivers/clocksource/timer-riscv.c b/drivers/clocksource/timer-riscv.c
index c4f15c4068c0..6b82f2e41f8e 100644
--- a/drivers/clocksource/timer-riscv.c
+++ b/drivers/clocksource/timer-riscv.c
@@ -14,7 +14,10 @@
 #include <linux/irq.h>
 #include <linux/sched_clock.h>
 #include <linux/io-64-nonatomic-lo-hi.h>
-#include <asm/smp.h>
+#include <linux/irqdomain.h>
+#include <linux/interrupt.h>
+#include <linux/of.h>
+#include <linux/of_irq.h>
 #include <asm/sbi.h>
 
 u64 __iomem *riscv_time_cmp;
@@ -39,6 +42,7 @@ static int riscv_clock_next_event(unsigned long delta,
 	return 0;
 }
 
+static unsigned int riscv_clock_event_irq;
 static DEFINE_PER_CPU(struct clock_event_device, riscv_clock_event) = {
 	.name			= "riscv_timer_clockevent",
 	.features		= CLOCK_EVT_FEAT_ONESHOT,
@@ -74,65 +78,86 @@ static int riscv_timer_starting_cpu(unsigned int cpu)
 	struct clock_event_device *ce = per_cpu_ptr(&riscv_clock_event, cpu);
 
 	ce->cpumask = cpumask_of(cpu);
+	ce->irq = riscv_clock_event_irq;
 	clockevents_config_and_register(ce, riscv_timebase, 100, 0x7fffffff);
 
-	csr_set(CSR_IE, IE_TIE);
+	enable_percpu_irq(riscv_clock_event_irq,
+			  irq_get_trigger_type(riscv_clock_event_irq));
 	return 0;
 }
 
 static int riscv_timer_dying_cpu(unsigned int cpu)
 {
-	csr_clear(CSR_IE, IE_TIE);
+	disable_percpu_irq(riscv_clock_event_irq);
 	return 0;
 }
 
 /* called directly from the low-level interrupt handler */
-void riscv_timer_interrupt(void)
+static irqreturn_t riscv_timer_interrupt(int irq, void *dev_id)
 {
 	struct clock_event_device *evdev = this_cpu_ptr(&riscv_clock_event);
 
 	csr_clear(CSR_IE, IE_TIE);
 	evdev->event_handler(evdev);
+
+	return IRQ_HANDLED;
 }
 
 static int __init riscv_timer_init_dt(struct device_node *n)
 {
-	int cpuid, hartid, error;
-
-	hartid = riscv_of_processor_hartid(n);
-	if (hartid < 0) {
-		pr_warn("Not valid hartid for node [%pOF] error = [%d]\n",
-			n, hartid);
-		return hartid;
-	}
-
-	cpuid = riscv_hartid_to_cpuid(hartid);
-	if (cpuid < 0) {
-		pr_warn("Invalid cpuid for hartid [%d]\n", hartid);
-		return cpuid;
-	}
-
-	if (cpuid != smp_processor_id())
+	int error;
+	struct of_phandle_args oirq;
+
+	/*
+	 * Either we have one INTC DT node under each CPU DT node
+	 * or a single system wide INTC DT node. Irrespective to
+	 * number of INTC DT nodes, we only proceed if we are able
+	 * to find irq_domain of INTC.
+	 *
+	 * Once we have INTC irq_domain, we create mapping for timer
+	 * interrupt HWIRQ and request_percpu_irq() on it.
+	 */
+
+	if (!irq_find_host(n) || riscv_clock_event_irq)
 		return 0;
 
-	pr_info("%s: Registering clocksource cpuid [%d] hartid [%d]\n",
-	       __func__, cpuid, hartid);
+	oirq.np = n;
+	oirq.args_count = 1;
+	oirq.args[0] = RV_IRQ_TIMER;
+	riscv_clock_event_irq = irq_create_of_mapping(&oirq);
+	if (!riscv_clock_event_irq)
+		return -ENODEV;
+
 	error = clocksource_register_hz(&riscv_clocksource, riscv_timebase);
 	if (error) {
-		pr_err("RISCV timer register failed [%d] for cpu = [%d]\n",
-		       error, cpuid);
+		pr_err("registering clocksource failed [%d]\n", error);
 		return error;
 	}
 
 	sched_clock_register(riscv_sched_clock, 64, riscv_timebase);
 
+	error = request_percpu_irq(riscv_clock_event_irq,
+				   riscv_timer_interrupt,
+				   "riscv-timer", &riscv_clock_event);
+	if (error) {
+		pr_err("registering percpu irq failed [%d]\n", error);
+		return error;
+	}
+
 	error = cpuhp_setup_state(CPUHP_AP_RISCV_TIMER_STARTING,
 			 "clockevents/riscv/timer:starting",
 			 riscv_timer_starting_cpu, riscv_timer_dying_cpu);
-	if (error)
+	if (error) {
 		pr_err("cpu hp setup state failed for RISCV timer [%d]\n",
 		       error);
-	return error;
+		return error;
+	}
+
+	pr_info("running at %lu.%02luMHz frequency\n",
+		(unsigned long)riscv_timebase / 1000000,
+		(unsigned long)(riscv_timebase / 10000) % 100);
+
+	return 0;
 }
 
-TIMER_OF_DECLARE(riscv_timer, "riscv", riscv_timer_init_dt);
+TIMER_OF_DECLARE(riscv_timer, "riscv,cpu-intc", riscv_timer_init_dt);
diff --git a/drivers/irqchip/irq-riscv-intc.c b/drivers/irqchip/irq-riscv-intc.c
index a2523fc663b1..bbc950510840 100644
--- a/drivers/irqchip/irq-riscv-intc.c
+++ b/drivers/irqchip/irq-riscv-intc.c
@@ -21,20 +21,12 @@ static atomic_t intc_init = ATOMIC_INIT(0);
 
 static asmlinkage void riscv_intc_irq(struct pt_regs *regs)
 {
-	struct pt_regs *old_regs;
 	unsigned long cause = regs->cause & ~CAUSE_IRQ_FLAG;
 
 	if (unlikely(cause >= BITS_PER_LONG))
 		panic("unexpected interrupt cause");
 
 	switch (cause) {
-	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:
 		/*
-- 
2.17.1