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Subject[RFC PATCH 5/5] clocksource: riscv_timer: Make timer interrupt as a per-CPU interrupt
Date
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@brainfault.org>
---
arch/riscv/include/asm/irq.h | 2 -
drivers/clocksource/riscv_timer.c | 76 +++++++++++++++++++++++++------
drivers/irqchip/irq-riscv-intc.c | 8 ----
3 files changed, 62 insertions(+), 24 deletions(-)

diff --git a/arch/riscv/include/asm/irq.h b/arch/riscv/include/asm/irq.h
index fe503d71876a..7ff3751e7816 100644
--- a/arch/riscv/include/asm/irq.h
+++ b/arch/riscv/include/asm/irq.h
@@ -30,8 +30,6 @@
*/
#define INTERRUPT_CAUSE_FLAG (1UL << (__riscv_xlen - 1))

-void riscv_timer_interrupt(void);
-
#include <asm-generic/irq.h>

#endif /* _ASM_RISCV_IRQ_H */
diff --git a/drivers/clocksource/riscv_timer.c b/drivers/clocksource/riscv_timer.c
index 4e8b347e43e2..c7ac60a82754 100644
--- a/drivers/clocksource/riscv_timer.c
+++ b/drivers/clocksource/riscv_timer.c
@@ -3,11 +3,17 @@
* Copyright (C) 2012 Regents of the University of California
* Copyright (C) 2017 SiFive
*/
+#define pr_fmt(fmt) "riscv-timer: " fmt
#include <linux/clocksource.h>
#include <linux/clockchips.h>
#include <linux/cpu.h>
#include <linux/delay.h>
#include <linux/irq.h>
+#include <linux/irqdomain.h>
+#include <linux/interrupt.h>
+#include <linux/of.h>
+#include <linux/of_irq.h>
+#include <linux/sched_clock.h>
#include <asm/sbi.h>

/*
@@ -31,6 +37,7 @@ 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,
@@ -38,6 +45,11 @@ static DEFINE_PER_CPU(struct clock_event_device, riscv_clock_event) = {
.set_next_event = riscv_clock_next_event,
};

+static u64 riscv_sched_clock(void)
+{
+ return get_cycles64();
+}
+
/*
* It is guaranteed that all the timers across all the harts are synchronized
* within one tick of each other, so while this could technically go
@@ -48,7 +60,7 @@ static unsigned long long riscv_clocksource_rdtime(struct clocksource *cs)
return get_cycles64();
}

-static DEFINE_PER_CPU(struct clocksource, riscv_clocksource) = {
+static struct clocksource riscv_clocksource = {
.name = "riscv_clocksource",
.rating = 300,
.mask = CLOCKSOURCE_MASK(BITS_PER_LONG),
@@ -61,45 +73,81 @@ 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(sie, SIE_STIE);
+ enable_percpu_irq(riscv_clock_event_irq, IRQ_TYPE_NONE);
return 0;
}

static int riscv_timer_dying_cpu(unsigned int cpu)
{
- csr_clear(sie, SIE_STIE);
+ 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(sie, SIE_STIE);
evdev->event_handler(evdev);
+
+ return IRQ_HANDLED;
}

static int __init riscv_timer_init_dt(struct device_node *n)
{
- int cpu_id = riscv_of_processor_hart(n), error;
- struct clocksource *cs;
-
- if (cpu_id != smp_processor_id())
+ int error;
+ struct irq_domain *domain;
+ 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 (riscv_clock_event_irq)
return 0;

- cs = per_cpu_ptr(&riscv_clocksource, cpu_id);
- clocksource_register_hz(cs, riscv_timebase);
+ oirq.np = n;
+ oirq.args_count = 1;
+ oirq.args[0] = INTERRUPT_CAUSE_TIMER;
+
+ domain = irq_find_host(oirq.np);
+ if (!domain)
+ return -ENODEV;
+
+ riscv_clock_event_irq = irq_create_of_mapping(&oirq);
+ if (!riscv_clock_event_irq)
+ return -ENODEV;
+
+ clocksource_register_hz(&riscv_clocksource, riscv_timebase);
+ sched_clock_register(riscv_sched_clock,
+ BITS_PER_LONG, riscv_timebase);
+
+ error = request_percpu_irq(riscv_clock_event_irq,
+ riscv_timer_interrupt,
+ "riscv_timer", &riscv_clock_event);
+ if (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)
- pr_err("RISCV timer register failed [%d] for cpu = [%d]\n",
- error, cpu_id);
+ pr_err("RISCV timer register failed error %d\n", error);
+
+ pr_info("running at %lu.%02luMHz frequency\n",
+ (unsigned long)riscv_timebase / 1000000,
+ (unsigned long)(riscv_timebase / 10000) % 100);
+
return error;
}

-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 c80502a1e12b..f40827a27227 100644
--- a/drivers/irqchip/irq-riscv-intc.c
+++ b/drivers/irqchip/irq-riscv-intc.c
@@ -22,20 +22,12 @@ static atomic_t intc_init = ATOMIC_INIT(0);

static void riscv_intc_irq(struct pt_regs *regs)
{
- struct pt_regs *old_regs;
unsigned long cause = regs->scause & ~INTERRUPT_CAUSE_FLAG;

if (unlikely(cause >= BITS_PER_LONG))
panic("unexpected interrupt cause");

switch (cause) {
- case INTERRUPT_CAUSE_TIMER:
- old_regs = set_irq_regs(regs);
- irq_enter();
- riscv_timer_interrupt();
- irq_exit();
- set_irq_regs(old_regs);
- break;
#ifdef CONFIG_SMP
case INTERRUPT_CAUSE_SOFTWARE:
/*
--
2.17.1
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