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SubjectRe: [PATCH 11/11] clocksource: new RISC-V SBI timer driver
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Date
On 8/2/18 4:51 AM, Christoph Hellwig wrote:
> 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, minor cleanups, merged
> hotplug cpu and other improvements from Atish]
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
> arch/riscv/include/asm/smp.h | 3 -
> arch/riscv/kernel/irq.c | 3 +
> arch/riscv/kernel/smpboot.c | 1 -
> arch/riscv/kernel/time.c | 8 +-
> drivers/clocksource/Kconfig | 11 +++
> drivers/clocksource/Makefile | 1 +
> drivers/clocksource/riscv_timer.c | 119 ++++++++++++++++++++++++++++++
> include/linux/cpuhotplug.h | 1 +
> 8 files changed, 136 insertions(+), 11 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 1bb01dc2d0f1..94e9ca18f5fa 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);
> -}
> -
> static long __init timebase_frequency(void)
> {
> struct device_node *cpu;
> @@ -43,5 +37,5 @@ void __init time_init(void)
> {
> riscv_timebase = timebase_frequency();
> 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..c1e46170c068
> --- /dev/null
> +++ b/drivers/clocksource/riscv_timer.c
> @@ -0,0 +1,119 @@
> +// 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 guarnteed that all the timers across all the harts are synchronized

/s/guarnteed/guaranteed
> + * 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 riscv_timer_hart_id(struct device_node *dev)
> +{
> + u32 hart;
> +
> + if (!dev)
> + return -1;
> + if (!of_device_is_compatible(dev, "riscv"))
> + return -1;
> + if (of_property_read_u32(dev, "reg", &hart))
> + return -1;
> +
> + return hart;
> +}
> +
> +static int __init riscv_timer_init_dt(struct device_node *n)
> +{
> + int cpu_id = riscv_timer_hart_id(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,
>

Otherwise, FWIW

Reviewed-by: Atish Patra <atish.patra@wdc.com>

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