linux-kernel - Re: [PATCH 09/17] clocksource/timer-riscv: New RISC-V Clocksource

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Date:   Wed, 7 Jun 2017 10:43:09 +0100
From:   Marc Zyngier <marc.zyngier@....com>
To:     Palmer Dabbelt <palmer@...belt.com>, linux-arch@...r.kernel.org,
        linux-kernel@...r.kernel.org, Arnd Bergmann <arnd@...db.de>,
        olof@...om.net
Cc:     albert@...ive.com, patches@...ups.riscv.org
Subject: Re: [PATCH 09/17] clocksource/timer-riscv: New RISC-V Clocksource

On 06/06/17 23:59, Palmer Dabbelt wrote:
> The RISC-V ISA defines a single RTC as well as an SBI oneshot timer.
> This timer is present on all RISC-V systems.
> 
> Signed-off-by: Palmer Dabbelt <palmer@...belt.com>
> ---
>  drivers/clocksource/Kconfig       |   8 +++
>  drivers/clocksource/Makefile      |   1 +
>  drivers/clocksource/timer-riscv.c | 118 ++++++++++++++++++++++++++++++++++++++
>  3 files changed, 127 insertions(+)
>  create mode 100644 drivers/clocksource/timer-riscv.c
> 
> diff --git a/drivers/clocksource/Kconfig b/drivers/clocksource/Kconfig
> index 545d541ae20e..1c2c6e7c7fab 100644
> --- a/drivers/clocksource/Kconfig
> +++ b/drivers/clocksource/Kconfig
> @@ -612,4 +612,12 @@ config CLKSRC_ST_LPC
>  	  Enable this option to use the Low Power controller timer
>  	  as clocksource.
>  
> +config CLKSRC_RISCV
> +	#bool "Clocksource for the RISC-V platform"
> +	def_bool y if RISCV
> +	depends on RISCV
> +	help
> +	  This enables a clocksource based on the RISC-V SBI timer, which is
> +	  built in to all RISC-V systems.
> +
>  endmenu
> diff --git a/drivers/clocksource/Makefile b/drivers/clocksource/Makefile
> index 2b5b56a6f00f..408ed9d314dc 100644
> --- a/drivers/clocksource/Makefile
> +++ b/drivers/clocksource/Makefile
> @@ -73,3 +73,4 @@ obj-$(CONFIG_H8300_TMR16)		+= h8300_timer16.o
>  obj-$(CONFIG_H8300_TPU)			+= h8300_tpu.o
>  obj-$(CONFIG_CLKSRC_ST_LPC)		+= clksrc_st_lpc.o
>  obj-$(CONFIG_X86_NUMACHIP)		+= numachip.o
> +obj-$(CONFIG_CLKSRC_RISCV)		+= timer-riscv.o
> diff --git a/drivers/clocksource/timer-riscv.c b/drivers/clocksource/timer-riscv.c
> new file mode 100644
> index 000000000000..04ef7b9130b3
> --- /dev/null
> +++ b/drivers/clocksource/timer-riscv.c
> @@ -0,0 +1,118 @@
> +/*
> + * Copyright (C) 2012 Regents of the University of California
> + * Copyright (C) 2017 SiFive
> + *
> + *   This program is free software; you can redistribute it and/or
> + *   modify it under the terms of the GNU General Public License
> + *   as published by the Free Software Foundation, version 2.
> + *
> + *   This program is distributed in the hope that it will be useful,
> + *   but WITHOUT ANY WARRANTY; without even the implied warranty of
> + *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> + *   GNU General Public License for more details.
> + */
> +
> +#include <linux/clocksource.h>
> +#include <linux/clockchips.h>
> +#include <linux/interrupt.h>
> +#include <linux/irq.h>
> +#include <linux/delay.h>
> +#include <linux/of.h>
> +
> +#include <asm/irq.h>
> +#include <asm/csr.h>
> +#include <asm/sbi.h>
> +#include <asm/delay.h>
> +
> +unsigned long riscv_timebase;
> +
> +static DEFINE_PER_CPU(struct clock_event_device, clock_event);
> +
> +static int riscv_timer_set_next_event(unsigned long delta,
> +	struct clock_event_device *evdev)
> +{
> +	sbi_set_timer(get_cycles() + delta);
> +	return 0;
> +}
> +
> +static int riscv_timer_set_oneshot(struct clock_event_device *evt)
> +{
> +	/* no-op; only one mode */
> +	return 0;
> +}
> +
> +static int riscv_timer_set_shutdown(struct clock_event_device *evt)
> +{
> +	/* can't stop the clock! */
> +	return 0;
> +}
> +
> +static u64 riscv_rdtime(struct clocksource *cs)
> +{
> +	return get_cycles();
> +}
> +
> +static struct clocksource riscv_clocksource = {
> +	.name = "riscv_clocksource",
> +	.rating = 300,
> +	.read = riscv_rdtime,
> +#ifdef CONFIG_64BITS
> +	.mask = CLOCKSOURCE_MASK(64),
> +#else
> +	.mask = CLOCKSOURCE_MASK(32),
> +#endif /* CONFIG_64BITS */
> +	.flags = CLOCK_SOURCE_IS_CONTINUOUS,
> +};
> +
> +void riscv_timer_interrupt(void)
> +{
> +	int cpu = smp_processor_id();
> +	struct clock_event_device *evdev = &per_cpu(clock_event, cpu);
> +
> +	evdev->event_handler(evdev);
> +}
> +
> +void __init init_clockevent(void)
> +{
> +	int cpu = smp_processor_id();
> +	struct clock_event_device *ce = &per_cpu(clock_event, cpu);
> +
> +	*ce = (struct clock_event_device){
> +		.name = "riscv_timer_clockevent",
> +		.features = CLOCK_EVT_FEAT_ONESHOT,
> +		.rating = 300,
> +		.cpumask = cpumask_of(cpu),
> +		.set_next_event = riscv_timer_set_next_event,
> +		.set_state_oneshot  = riscv_timer_set_oneshot,
> +		.set_state_shutdown = riscv_timer_set_shutdown,
> +	};
> +
> +	/* Enable timer interrupts */
> +	csr_set(sie, SIE_STIE);
> +
> +	clockevents_config_and_register(ce, riscv_timebase, 100, 0x7fffffff);
> +}
> +
> +static unsigned long __init of_timebase(void)
> +{
> +	struct device_node *cpu;
> +	const __be32 *prop;
> +
> +	cpu = of_find_node_by_path("/cpus");
> +	if (cpu) {
> +		prop = of_get_property(cpu, "timebase-frequency", NULL);
> +		if (prop)
> +			return be32_to_cpu(*prop);

Consider using of_property_read_u32() instead.

> +	}
> +
> +	return 10000000;

Is this an architectural guarantee? Or something that is implementation
specific?

> +}
> +
> +void __init time_init(void)
> +{
> +	riscv_timebase = of_timebase();
> +	lpj_fine = riscv_timebase / HZ;
> +
> +	clocksource_register_hz(&riscv_clocksource, riscv_timebase);
> +	init_clockevent();
> +}
> 

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...