Re: [PATCH v3 2/4] clocksource/drivers: Add CLINT timer driver

[Anup Patel <anup@brainfault.org>]

On Fri, Jul 17, 2020 at 10:58 AM Daniel Lezcano
<daniel.lezcano@linaro.org> wrote:
>
> On 17/07/2020 07:21, Anup Patel wrote:
> > On Fri, Jul 17, 2020 at 2:57 AM Daniel Lezcano
> > <daniel.lezcano@linaro.org> wrote:
> >>
> >>
> >> Hi Anup,
> >>
> >>
> >> On 15/07/2020 09:15, Anup Patel wrote:
> >>> The TIME CSR and SBI calls are not available in RISC-V M-mode so we
> >>> separate add CLINT driver for Linux RISC-V M-mode (i.e. RISC-V NoMMU
> >>> kernel).
> >>
> >> The description is confusing, please reword it and give a bit more
> >> information about the timer itself, especially, the IPI thing.
> >
> > Okay, will update.
> >
> >>
> >>> Signed-off-by: Anup Patel <anup.patel@wdc.com>
> >>> ---
> >>>  drivers/clocksource/Kconfig       |  10 ++
> >>>  drivers/clocksource/Makefile      |   1 +
> >>>  drivers/clocksource/timer-clint.c | 229 ++++++++++++++++++++++++++++++
> >>>  include/linux/cpuhotplug.h        |   1 +
> >>>  4 files changed, 241 insertions(+)
> >>>  create mode 100644 drivers/clocksource/timer-clint.c
> >>>
> >>> diff --git a/drivers/clocksource/Kconfig b/drivers/clocksource/Kconfig
> >>> index 91418381fcd4..eabcf1cfb0c0 100644
> >>> --- a/drivers/clocksource/Kconfig
> >>> +++ b/drivers/clocksource/Kconfig
> >>> @@ -658,6 +658,16 @@ config RISCV_TIMER
> >>>         is accessed via both the SBI and the rdcycle instruction.  This is
> >>>         required for all RISC-V systems.
> >>>
> >>> +config CLINT_TIMER
> >>> +     bool "Timer for the RISC-V platform"
> >>> +     depends on GENERIC_SCHED_CLOCK && RISCV_M_MODE
> >>> +     default y
> >>> +     select TIMER_PROBE
> >>> +     select TIMER_OF
> >>> +     help
> >>> +       This option enables the CLINT timer for RISC-V systems. The CLINT
> >>> +       driver is usually used for NoMMU RISC-V systems.
> >>
> >> For the timer, we do silent option and let the platform config select
> >> it. Please refer to other timer option below as reference.
> >
> > Okay, I will use "default RISCV" instead of "default y" (just like other
> > timer Kconfig options).
>
> Preferably, select it from the platform's Kconfig.

Okay, I will update.

>
> >>
> >>>  config CSKY_MP_TIMER
> >>>       bool "SMP Timer for the C-SKY platform" if COMPILE_TEST
> >>>       depends on CSKY
> >>> diff --git a/drivers/clocksource/Makefile b/drivers/clocksource/Makefile
> >>> index bdda1a2e4097..18e700e703a0 100644
> >>> --- a/drivers/clocksource/Makefile
> >>> +++ b/drivers/clocksource/Makefile
> >>> @@ -87,6 +87,7 @@ 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)            += timer-riscv.o
> >>> +obj-$(CONFIG_CLINT_TIMER)            += timer-clint.o
> >>>  obj-$(CONFIG_CSKY_MP_TIMER)          += timer-mp-csky.o
> >>>  obj-$(CONFIG_GX6605S_TIMER)          += timer-gx6605s.o
> >>>  obj-$(CONFIG_HYPERV_TIMER)           += hyperv_timer.o
> >>> diff --git a/drivers/clocksource/timer-clint.c b/drivers/clocksource/timer-clint.c
> >>> new file mode 100644
> >>> index 000000000000..bfc38bb5a589
> >>> --- /dev/null
> >>> +++ b/drivers/clocksource/timer-clint.c
> >>> @@ -0,0 +1,229 @@
> >>> +// SPDX-License-Identifier: GPL-2.0
> >>> +/*
> >>> + * Copyright (C) 2020 Western Digital Corporation or its affiliates.
> >>> + *
> >>> + * Most of the M-mode (i.e. NoMMU) RISC-V systems usually have a
> >>> + * CLINT MMIO timer device.
> >>> + */
> >>> +
> >>> +#define pr_fmt(fmt) "clint: " fmt
> >>> +#include <linux/bitops.h>
> >>> +#include <linux/clocksource.h>
> >>> +#include <linux/clockchips.h>
> >>> +#include <linux/cpu.h>
> >>> +#include <linux/delay.h>
> >>> +#include <linux/module.h>
> >>> +#include <linux/of_address.h>
> >>> +#include <linux/sched_clock.h>
> >>> +#include <linux/io-64-nonatomic-lo-hi.h>
> >>> +#include <linux/interrupt.h>
> >>> +#include <linux/of_irq.h>
> >>> +#include <linux/smp.h>
> >>> +
> >>> +#define CLINT_IPI_OFF                0
> >>> +#define CLINT_TIMER_CMP_OFF  0x4000
> >>> +#define CLINT_TIMER_VAL_OFF  0xbff8
> >>> +
> >>> +/* CLINT manages IPI and Timer for RISC-V M-mode  */
> >>> +static u32 __iomem *clint_ipi_base;
> >>> +static u64 __iomem *clint_timer_cmp;
> >>> +static u64 __iomem *clint_timer_val;
> >>> +static unsigned long clint_timer_freq;
> >>> +static unsigned int clint_timer_irq;
> >>> +
> >>> +static void clint_send_ipi(const struct cpumask *target)
> >>> +{
> >>> +     unsigned int cpu;
> >>> +
> >>> +     for_each_cpu(cpu, target)
> >>> +             writel(1, clint_ipi_base + cpuid_to_hartid_map(cpu));
> >>> +}
> >>> +
> >>> +static void clint_clear_ipi(void)
> >>> +{
> >>> +     writel(0, clint_ipi_base + cpuid_to_hartid_map(smp_processor_id()));
> >>> +}
> >>> +
> >>> +static struct riscv_ipi_ops clint_ipi_ops = {
> >>> +     .ipi_inject = clint_send_ipi,
> >>> +     .ipi_clear = clint_clear_ipi,
> >>> +};
> >>> +
> >>> +#ifdef CONFIG_64BIT
> >>> +#define clint_get_cycles()   readq_relaxed(clint_timer_val)
> >>> +#else
> >>> +#define clint_get_cycles()   readl_relaxed(clint_timer_val)
> >>> +#define clint_get_cycles_hi()        readl_relaxed(((u32 *)clint_timer_val) + 1)
> >>> +#endif
> >>> +
> >>> +#ifdef CONFIG_64BIT
> >>> +static u64 clint_get_cycles64(void)
> >>> +{
> >>> +     return clint_get_cycles();
> >>> +}
> >>> +#else /* CONFIG_64BIT */
> >>> +static u64 clint_get_cycles64(void)
> >>> +{
> >>> +     u32 hi, lo;
> >>> +
> >>> +     do {
> >>> +             hi = clint_get_cycles_hi();
> >>> +             lo = clint_get_cycles();
> >>> +     } while (hi != clint_get_cycles_hi());
> >>> +
> >>> +     return ((u64)hi << 32) | lo;
> >>> +}
> >>> +#endif /* CONFIG_64BIT */
> >>> +static int clint_clock_next_event(unsigned long delta,
> >>> +                                struct clock_event_device *ce)
> >>> +{
> >>> +     void __iomem *r = clint_timer_cmp +
> >>> +                       cpuid_to_hartid_map(smp_processor_id());
> >>> +
> >>> +     csr_set(CSR_IE, IE_TIE);
> >>> +     writeq_relaxed(clint_get_cycles64() + delta, r);
> >>> +     return 0;
> >>> +}
> >>> +
> >>> +static DEFINE_PER_CPU(struct clock_event_device, clint_clock_event) = {
> >>> +     .name                   = "clint_clockevent",
> >>> +     .features               = CLOCK_EVT_FEAT_ONESHOT,
> >>> +     .rating         = 100,
> >>> +     .set_next_event = clint_clock_next_event,
> >>> +};
> >>> +
> >>> +static u64 clint_rdtime(struct clocksource *cs)
> >>> +{
> >>> +     return readq_relaxed(clint_timer_val);
> >>> +}
> >>> +
> >>> +static u64 notrace clint_sched_clock(void)
> >>> +{
> >>> +     return readq_relaxed(clint_timer_val);
> >>> +}
> >>> +
> >>> +static struct clocksource clint_clocksource = {
> >>> +     .name           = "clint_clocksource",
> >>> +     .rating = 300,
> >>> +     .mask           = CLOCKSOURCE_MASK(64),
> >>> +     .flags          = CLOCK_SOURCE_IS_CONTINUOUS,
> >>> +     .read           = clint_rdtime,
> >>
> >> What if !CONFIG_64BIT
> >
> > The CLINT counter is 64bit for both 32bit and 64bit systems
> > but I should have used clint_get_cycles64() in clint_rdtime().
> > I will update it.
> >
> >>
> >>> +};
> >>> +
> >>> +static int clint_timer_starting_cpu(unsigned int cpu)
> >>> +{
> >>> +     struct clock_event_device *ce = per_cpu_ptr(&clint_clock_event, cpu);
> >>> +
> >>> +     ce->cpumask = cpumask_of(cpu);
> >>> +     clockevents_config_and_register(ce, clint_timer_freq, 200, ULONG_MAX);
> >>
> >> The function is not immune against registering the same clockevents. If
> >> the CPU is hotplugged several times, this function will be called again
> >> and again. Why not rely on a for_each_possible_cpu loop in the init
> >> function ?
> >>
> >>> +     enable_percpu_irq(clint_timer_irq,
> >>> +                       irq_get_trigger_type(clint_timer_irq));
> >>
> >> Why do you want to enable / disable the interrrupts ? The should be
> >> already handle by the hotplug framework no ?
> >
> > The perCPU interrupts are not enabled by default. We have to
> > explicitly enable/disable perCPU interrupts in CPU hotplug callbacks.
> >
>
> Isn't is possible to do that in the probe/init function ?

The enable_percpu_irq() and disable_percpu_irq() work for current
CPU only. This means we have to call these functions separately on
each CPU.

>
>
>
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