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Subject[PATCH 8/8] clocksource: new RISC-V SBI timer driver
Date
From: Palmer Dabbelt <palmer@dabbelt.com>

The RISC-V ISA defines a per-hart real-time clock and timer, which is
present on all systems. The clock is accessed via the 'rdtime'
pseudo-instruction (which reads a CSR), and the timer is set via an SBI
call.

Contains various improvements from Atish Patra <atish.patra@wdc.com>.

Signed-off-by: Dmitriy Cherkasov <dmitriy@oss-tech.org>
Signed-off-by: Palmer Dabbelt <palmer@dabbelt.com>
[hch: remove dead code, add SPDX tags, used riscv_of_processor_hart(),
minor cleanups, merged hotplug cpu support and other improvements
from Atish]
Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Atish Patra <atish.patra@wdc.com>
---
arch/riscv/include/asm/smp.h | 3 -
arch/riscv/kernel/irq.c | 3 +
arch/riscv/kernel/smpboot.c | 1 -
arch/riscv/kernel/time.c | 9 +--
drivers/clocksource/Kconfig | 11 ++++
drivers/clocksource/Makefile | 1 +
drivers/clocksource/riscv_timer.c | 105 ++++++++++++++++++++++++++++++
include/linux/cpuhotplug.h | 1 +
8 files changed, 122 insertions(+), 12 deletions(-)
create mode 100644 drivers/clocksource/riscv_timer.c

diff --git a/arch/riscv/include/asm/smp.h b/arch/riscv/include/asm/smp.h
index c9395fff246f..36016845461d 100644
--- a/arch/riscv/include/asm/smp.h
+++ b/arch/riscv/include/asm/smp.h
@@ -24,9 +24,6 @@

#ifdef CONFIG_SMP

-/* SMP initialization hook for setup_arch */
-void __init init_clockevent(void);
-
/* SMP initialization hook for setup_arch */
void __init setup_smp(void);

diff --git a/arch/riscv/kernel/irq.c b/arch/riscv/kernel/irq.c
index ab5f3e22c7cc..0cfac48a1272 100644
--- a/arch/riscv/kernel/irq.c
+++ b/arch/riscv/kernel/irq.c
@@ -30,6 +30,9 @@ asmlinkage void __irq_entry do_IRQ(struct pt_regs *regs, unsigned long cause)

irq_enter();
switch (cause & ~INTERRUPT_CAUSE_FLAG) {
+ case INTERRUPT_CAUSE_TIMER:
+ riscv_timer_interrupt();
+ break;
#ifdef CONFIG_SMP
case INTERRUPT_CAUSE_SOFTWARE:
/*
diff --git a/arch/riscv/kernel/smpboot.c b/arch/riscv/kernel/smpboot.c
index f741458c5a3f..56abab6a9812 100644
--- a/arch/riscv/kernel/smpboot.c
+++ b/arch/riscv/kernel/smpboot.c
@@ -104,7 +104,6 @@ asmlinkage void __init smp_callin(void)
current->active_mm = mm;

trap_init();
- init_clockevent();
notify_cpu_starting(smp_processor_id());
set_cpu_online(smp_processor_id(), 1);
local_flush_tlb_all();
diff --git a/arch/riscv/kernel/time.c b/arch/riscv/kernel/time.c
index 0df9b2cbd645..1911c8f6b8a6 100644
--- a/arch/riscv/kernel/time.c
+++ b/arch/riscv/kernel/time.c
@@ -18,12 +18,6 @@

unsigned long riscv_timebase;

-void __init init_clockevent(void)
-{
- timer_probe();
- csr_set(sie, SIE_STIE);
-}
-
void __init time_init(void)
{
struct device_node *cpu;
@@ -35,6 +29,5 @@ void __init time_init(void)
riscv_timebase = prop;

lpj_fine = riscv_timebase / HZ;
-
- init_clockevent();
+ timer_probe();
}
diff --git a/drivers/clocksource/Kconfig b/drivers/clocksource/Kconfig
index dec0dd88ec15..a11f4ba98b05 100644
--- a/drivers/clocksource/Kconfig
+++ b/drivers/clocksource/Kconfig
@@ -609,4 +609,15 @@ config ATCPIT100_TIMER
help
This option enables support for the Andestech ATCPIT100 timers.

+config RISCV_TIMER
+ bool "Timer for the RISC-V platform"
+ depends on RISCV
+ default y
+ select TIMER_PROBE
+ select TIMER_OF
+ help
+ This enables the per-hart timer built into all RISC-V systems, which
+ is accessed via both the SBI and the rdcycle instruction. This is
+ required for all RISC-V systems.
+
endmenu
diff --git a/drivers/clocksource/Makefile b/drivers/clocksource/Makefile
index 00caf37e52f9..ded31f720bd9 100644
--- a/drivers/clocksource/Makefile
+++ b/drivers/clocksource/Makefile
@@ -78,3 +78,4 @@ obj-$(CONFIG_H8300_TPU) += h8300_tpu.o
obj-$(CONFIG_CLKSRC_ST_LPC) += clksrc_st_lpc.o
obj-$(CONFIG_X86_NUMACHIP) += numachip.o
obj-$(CONFIG_ATCPIT100_TIMER) += timer-atcpit100.o
+obj-$(CONFIG_RISCV_TIMER) += riscv_timer.o
diff --git a/drivers/clocksource/riscv_timer.c b/drivers/clocksource/riscv_timer.c
new file mode 100644
index 000000000000..4e8b347e43e2
--- /dev/null
+++ b/drivers/clocksource/riscv_timer.c
@@ -0,0 +1,105 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2012 Regents of the University of California
+ * Copyright (C) 2017 SiFive
+ */
+#include <linux/clocksource.h>
+#include <linux/clockchips.h>
+#include <linux/cpu.h>
+#include <linux/delay.h>
+#include <linux/irq.h>
+#include <asm/sbi.h>
+
+/*
+ * All RISC-V systems have a timer attached to every hart. These timers can be
+ * read by the 'rdcycle' pseudo instruction, and can use the SBI to setup
+ * events. In order to abstract the architecture-specific timer reading and
+ * setting functions away from the clock event insertion code, we provide
+ * function pointers to the clockevent subsystem that perform two basic
+ * operations: rdtime() reads the timer on the current CPU, and
+ * next_event(delta) sets the next timer event to 'delta' cycles in the future.
+ * As the timers are inherently a per-cpu resource, these callbacks perform
+ * operations on the current hart. There is guaranteed to be exactly one timer
+ * per hart on all RISC-V systems.
+ */
+
+static int riscv_clock_next_event(unsigned long delta,
+ struct clock_event_device *ce)
+{
+ csr_set(sie, SIE_STIE);
+ sbi_set_timer(get_cycles64() + delta);
+ return 0;
+}
+
+static DEFINE_PER_CPU(struct clock_event_device, riscv_clock_event) = {
+ .name = "riscv_timer_clockevent",
+ .features = CLOCK_EVT_FEAT_ONESHOT,
+ .rating = 100,
+ .set_next_event = riscv_clock_next_event,
+};
+
+/*
+ * 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
+ * backwards when hopping between CPUs, practically it won't happen.
+ */
+static unsigned long long riscv_clocksource_rdtime(struct clocksource *cs)
+{
+ return get_cycles64();
+}
+
+static DEFINE_PER_CPU(struct clocksource, riscv_clocksource) = {
+ .name = "riscv_clocksource",
+ .rating = 300,
+ .mask = CLOCKSOURCE_MASK(BITS_PER_LONG),
+ .flags = CLOCK_SOURCE_IS_CONTINUOUS,
+ .read = riscv_clocksource_rdtime,
+};
+
+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);
+ clockevents_config_and_register(ce, riscv_timebase, 100, 0x7fffffff);
+
+ csr_set(sie, SIE_STIE);
+ return 0;
+}
+
+static int riscv_timer_dying_cpu(unsigned int cpu)
+{
+ csr_clear(sie, SIE_STIE);
+ return 0;
+}
+
+/* called directly from the low-level interrupt handler */
+void riscv_timer_interrupt(void)
+{
+ struct clock_event_device *evdev = this_cpu_ptr(&riscv_clock_event);
+
+ csr_clear(sie, SIE_STIE);
+ evdev->event_handler(evdev);
+}
+
+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())
+ return 0;
+
+ cs = per_cpu_ptr(&riscv_clocksource, cpu_id);
+ clocksource_register_hz(cs, riscv_timebase);
+
+ 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);
+ return error;
+}
+
+TIMER_OF_DECLARE(riscv_timer, "riscv", riscv_timer_init_dt);
diff --git a/include/linux/cpuhotplug.h b/include/linux/cpuhotplug.h
index 8796ba387152..554c27f6cfbd 100644
--- a/include/linux/cpuhotplug.h
+++ b/include/linux/cpuhotplug.h
@@ -125,6 +125,7 @@ enum cpuhp_state {
CPUHP_AP_MARCO_TIMER_STARTING,
CPUHP_AP_MIPS_GIC_TIMER_STARTING,
CPUHP_AP_ARC_TIMER_STARTING,
+ CPUHP_AP_RISCV_TIMER_STARTING,
CPUHP_AP_KVM_STARTING,
CPUHP_AP_KVM_ARM_VGIC_INIT_STARTING,
CPUHP_AP_KVM_ARM_VGIC_STARTING,
--
2.18.0
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