Re: [PATCH V9 3/8] clocksource: add C-SKY SMP timer

[Daniel Lezcano <daniel.lezcano@linaro.org>]

On 01/10/2018 03:35, Guo Ren wrote:
> This timer is used by SMP system and use mfcr/mtcr instruction
> to access the regs.
> 
> Changelog:
>  - Remove #define CPUHP_AP_CSKY_TIMER_STARTING
>  - Add CPUHP_AP_CSKY_TIMER_STARTING in cpuhotplug.h
>  - Support csky mp timer alpha version.
>  - Just use low-counter with 32bit width as clocksource.
>  - Coding convention with upstream feed-back.
> 
> Signed-off-by: Guo Ren <ren_guo@c-sky.com>
> ---
>  drivers/clocksource/Kconfig        |   8 ++
>  drivers/clocksource/Makefile       |   1 +
>  drivers/clocksource/csky_mptimer.c | 176 +++++++++++++++++++++++++++++++++++++
>  include/linux/cpuhotplug.h         |   1 +
>  4 files changed, 186 insertions(+)
>  create mode 100644 drivers/clocksource/csky_mptimer.c
> 
> diff --git a/drivers/clocksource/Kconfig b/drivers/clocksource/Kconfig
> index a11f4ba..a28043f 100644
> --- a/drivers/clocksource/Kconfig
> +++ b/drivers/clocksource/Kconfig
> @@ -620,4 +620,12 @@ config RISCV_TIMER
>  	  is accessed via both the SBI and the rdcycle instruction.  This is
>  	  required for all RISC-V systems.
>  
> +config CSKY_MPTIMER
> +	bool "C-SKY Multi Processor Timer"
> +	depends on CSKY
> +	select TIMER_OF
> +	help
> +	  Say yes here to enable C-SKY SMP timer driver used for C-SKY SMP
> +	  system.
> +
>  endmenu

The same rule applies here for COMPILE_TEST.

And please rename the file: timer-mp-csky.c

> diff --git a/drivers/clocksource/Makefile b/drivers/clocksource/Makefile
> index db51b24..848c676 100644
> --- a/drivers/clocksource/Makefile
> +++ b/drivers/clocksource/Makefile
> @@ -79,3 +79,4 @@ 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
> +obj-$(CONFIG_CSKY_MPTIMER)		+= csky_mptimer.o
> diff --git a/drivers/clocksource/csky_mptimer.c b/drivers/clocksource/csky_mptimer.c
> new file mode 100644
> index 0000000..9dc3cfb
> --- /dev/null
> +++ b/drivers/clocksource/csky_mptimer.c
> @@ -0,0 +1,176 @@
> +// SPDX-License-Identifier: GPL-2.0
> +// Copyright (C) 2018 Hangzhou C-SKY Microsystems co.,ltd.
> +
> +#include <linux/init.h>
> +#include <linux/interrupt.h>
> +#include <linux/sched_clock.h>
> +#include <linux/cpu.h>
> +#include <asm/reg_ops.h>
> +
> +#include "timer-of.h"
> +
> +#define PTIM_CCVR	"cr<3, 14>"
> +#define PTIM_CTLR	"cr<0, 14>"
> +#define PTIM_LVR	"cr<6, 14>"
> +#define PTIM_TSR	"cr<1, 14>"
> +
> +static int csky_mptimer_set_next_event(unsigned long delta, struct clock_event_device *ce)
> +{
> +	mtcr(PTIM_LVR, delta);
> +
> +	return 0;
> +}
> +
> +static int csky_mptimer_shutdown(struct clock_event_device *ce)
> +{
> +	mtcr(PTIM_CTLR, 0);
> +
> +	return 0;
> +}
> +
> +static int csky_mptimer_oneshot(struct clock_event_device *ce)
> +{
> +	mtcr(PTIM_CTLR, 1);
> +
> +	return 0;
> +}
> +
> +static int csky_mptimer_oneshot_stopped(struct clock_event_device *ce)
> +{
> +	mtcr(PTIM_CTLR, 0);
> +
> +	return 0;
> +}
> +
> +static DEFINE_PER_CPU(struct timer_of, csky_to) = {
> +	.flags					= TIMER_OF_CLOCK,
> +	.clkevt = {
> +		.rating				= 300,
> +		.features			= CLOCK_EVT_FEAT_PERCPU |
> +						  CLOCK_EVT_FEAT_ONESHOT,
> +		.set_state_shutdown		= csky_mptimer_shutdown,
> +		.set_state_oneshot		= csky_mptimer_oneshot,
> +		.set_state_oneshot_stopped	= csky_mptimer_oneshot_stopped,
> +		.set_next_event			= csky_mptimer_set_next_event,
> +	},
> +	.of_irq = {
> +		.flags				= IRQF_TIMER,
> +		.percpu				= 1,
> +	},

See comment in the init function.

> +};
> +
> +static irqreturn_t timer_interrupt(int irq, void *dev)
> +{
> +	struct timer_of *to = this_cpu_ptr(&csky_to);
> +
> +	mtcr(PTIM_TSR, 0);
> +
> +	to->clkevt.event_handler(&to->clkevt);
> +
> +	return IRQ_HANDLED;
> +}
> +
> +/*
> + * clock event for percpu
> + */
> +static int csky_mptimer_starting_cpu(unsigned int cpu)
> +{
> +	struct timer_of *to = per_cpu_ptr(&csky_to, cpu);
> +
> +	to->clkevt.cpumask = cpumask_of(cpu);
> +
> +	clockevents_config_and_register(&to->clkevt, timer_of_rate(to), 2, ULONG_MAX);
> +
> +	enable_percpu_irq(timer_of_irq(to), 0);
> +
> +	return 0;
> +}
> +
> +static int csky_mptimer_dying_cpu(unsigned int cpu)
> +{
> +	struct timer_of *to = per_cpu_ptr(&csky_to, cpu);
> +
> +	disable_percpu_irq(timer_of_irq(to));
> +
> +	return 0;
> +}
> +
> +/*
> + * clock source
> + */
> +static u64 sched_clock_read(void)
> +{
> +	return (u64) mfcr(PTIM_CCVR);

extra space

> +}
> +
> +static u64 clksrc_read(struct clocksource *c)
> +{
> +	return (u64) mfcr(PTIM_CCVR);

extra space

> +}
> +
> +struct clocksource csky_clocksource = {
> +	.name	= "csky",
> +	.rating	= 400,
> +	.mask	= CLOCKSOURCE_MASK(32),
> +	.flags	= CLOCK_SOURCE_IS_CONTINUOUS,
> +	.read	= clksrc_read,
> +};
> +
> +static int __init csky_mptimer_init(struct device_node *np)
> +{
> +	int ret, cpu;
> +	struct timer_of *to;
> +	int rate = 0;
> +	int irq	 = 0;
> +
> +	/*
> +	 * Csky_mptimer is designed for C-SKY SMP multi-processors and
> +	 * every core has it's own private irq and regs for clkevt and
> +	 * clksrc.
> +	 *
> +	 * The regs is accessed by cpu instruction: mfcr/mtcr instead of
> +	 * mmio map style. So we needn't mmio-address in dts, but we still
> +	 * need to give clk and irq number.
> +	 *
> +	 * We use private irq for the mptimer and irq number is the same
> +	 * for every core. So we use request_percpu_irq() in timer_of_init.
> +	 */
> +

extra line

> +	for_each_possible_cpu(cpu) {
> +		to = per_cpu_ptr(&csky_to, cpu);
> +
> +		if (cpu == 0) {
> +			to->flags	  |= TIMER_OF_IRQ;
> +			to->of_irq.handler = timer_interrupt;
> +
> +			ret = timer_of_init(np, to);
> +			if (ret)
> +				return ret;
> +
> +			rate	= timer_of_rate(to);
> +			irq	= to->of_irq.irq;
> +		} else {
> +			ret = timer_of_init(np, to);
> +			if (ret)
> +				return ret;
> +
> +			to->of_clk.rate	= rate;
> +			to->of_irq.irq	= irq;
> +		}
> +	}


Isn't possible to replace this loop which is a bit confusing by:

 - no irq flag specified for timer-of
 - request irq before

So we end up with:

	irq = irq_of_parse_and_map(np, 0);
	if (irq <= 0)
		return -EINVAL;

	ret = request_irq(irq, csky_timer_interrupt,
			IRQF_TIMER | IRQF_PERCPU,
                        "csky_mp_timer", &csky_to));
	if (ret)
		return ret;

	for_each_possible_cpu(cpu) {
		to = per_cpu_ptr(&csky_to, cpu);
		ret = timer_of_init(np, to);
		if (ret)
			goto rollback;
	}

Alternatively, you can remove the timer_of struct and instantiate the
percpu stuff in cpuhp callbacks (cf. jcore_pit).


> +	ret = cpuhp_setup_state(CPUHP_AP_CSKY_TIMER_STARTING,
> +				"clockevents/csky/timer:starting",
> +				csky_mptimer_starting_cpu,
> +				csky_mptimer_dying_cpu);
> +	if (ret) {
> +		pr_err("%s: Failed to cpuhp_setup_state.\n", __func__);
> +		return ret;
> +	}
> +
> +	clocksource_register_hz(&csky_clocksource, rate);
> +	sched_clock_register(sched_clock_read, 32, rate);
> +
> +	return 0;
> +}
> +TIMER_OF_DECLARE(csky_mptimer, "csky,mptimer", csky_mptimer_init);
> diff --git a/include/linux/cpuhotplug.h b/include/linux/cpuhotplug.h
> index caf40ad..e0cd2ba 100644
> --- a/include/linux/cpuhotplug.h
> +++ b/include/linux/cpuhotplug.h
> @@ -126,6 +126,7 @@ enum cpuhp_state {
>  	CPUHP_AP_MIPS_GIC_TIMER_STARTING,
>  	CPUHP_AP_ARC_TIMER_STARTING,
>  	CPUHP_AP_RISCV_TIMER_STARTING,
> +	CPUHP_AP_CSKY_TIMER_STARTING,
>  	CPUHP_AP_KVM_STARTING,
>  	CPUHP_AP_KVM_ARM_VGIC_INIT_STARTING,
>  	CPUHP_AP_KVM_ARM_VGIC_STARTING,
> 


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