Message-ID: <20161114112326.GC2016@mai>
Date:   Mon, 14 Nov 2016 12:23:26 +0100
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     Noam Camus <noamca@...lanox.com>
Cc:     robh+dt@...nel.org, mark.rutland@....com, tglx@...utronix.de,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 3/3] clocksource: Add clockevent support to NPS400
 driver

On Sun, Nov 13, 2016 at 09:24:32AM +0200, Noam Camus wrote:
> From: Noam Camus <noamca@...lanox.com>
> 
> Till now we used clockevent from generic ARC driver.
> This was enough as long as we worked with simple multicore SoC.
> When we are working with multithread SoC each HW thread can be
> scheduled to receive timer interrupt using timer mask register.
> This patch will provide a way to control clock events per HW thread.
> 
> The design idea is that for each core there is dedicated regirtser

s/regirtser/register/ (already spotted in v2).

> (TSI) serving all 16 HW threads.
> The register is a bitmask with one bit for each HW thread.
> When HW thread wants that next expiration of timer interrupt will
> hit it then the proper bit should be set in this dedicated register.
> When timer expires all HW threads within this core which their bit
> is set at the TSI register will be interrupted.
> 
> Driver can be used from device tree by:
> compatible = "ezchip,nps400-timer0" <-- for clocksource
> compatible = "ezchip,nps400-timer1" <-- for clockevent
> 
> Note that name convention for timer0/timer1 was taken from legacy
> ARC design. This design is our base before adding HW threads.
> For backward compatibility we keep "ezchip,nps400-timer" for clocksource
> 
> Signed-off-by: Noam Camus <noamca@...lanox.com>
> ---
>  .../bindings/timer/ezchip,nps400-timer.txt         |   15 --
>  .../bindings/timer/ezchip,nps400-timer0.txt        |   17 ++
>  .../bindings/timer/ezchip,nps400-timer1.txt        |   15 ++
>  drivers/clocksource/timer-nps.c                    |  213 ++++++++++++++++++++
>  4 files changed, 245 insertions(+), 15 deletions(-)
>  delete mode 100644 Documentation/devicetree/bindings/timer/ezchip,nps400-timer.txt
>  create mode 100644 Documentation/devicetree/bindings/timer/ezchip,nps400-timer0.txt
>  create mode 100644 Documentation/devicetree/bindings/timer/ezchip,nps400-timer1.txt
> 
> diff --git a/Documentation/devicetree/bindings/timer/ezchip,nps400-timer.txt b/Documentation/devicetree/bindings/timer/ezchip,nps400-timer.txt
> deleted file mode 100644
> index c8c03d7..0000000
> --- a/Documentation/devicetree/bindings/timer/ezchip,nps400-timer.txt
> +++ /dev/null
> @@ -1,15 +0,0 @@
> -NPS Network Processor
> -
> -Required properties:
> -
> -- compatible :	should be "ezchip,nps400-timer"
> -
> -Clocks required for compatible = "ezchip,nps400-timer":
> -- clocks : Must contain a single entry describing the clock input
> -
> -Example:
> -
> -timer {
> -	compatible = "ezchip,nps400-timer";
> -	clocks = <&sysclk>;
> -};
> diff --git a/Documentation/devicetree/bindings/timer/ezchip,nps400-timer0.txt b/Documentation/devicetree/bindings/timer/ezchip,nps400-timer0.txt
> new file mode 100644
> index 0000000..e3cfce8
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/timer/ezchip,nps400-timer0.txt
> @@ -0,0 +1,17 @@
> +NPS Network Processor
> +
> +Required properties:
> +
> +- compatible :	should be "ezchip,nps400-timer0"
> +
> +Clocks required for compatible = "ezchip,nps400-timer0":
> +- interrupts : The interrupt of the first timer
> +- clocks : Must contain a single entry describing the clock input
> +
> +Example:
> +
> +timer {
> +	compatible = "ezchip,nps400-timer0";
> +	interrupts = <3>;
> +	clocks = <&sysclk>;
> +};
> diff --git a/Documentation/devicetree/bindings/timer/ezchip,nps400-timer1.txt b/Documentation/devicetree/bindings/timer/ezchip,nps400-timer1.txt
> new file mode 100644
> index 0000000..c0ab419
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/timer/ezchip,nps400-timer1.txt
> @@ -0,0 +1,15 @@
> +NPS Network Processor
> +
> +Required properties:
> +
> +- compatible :	should be "ezchip,nps400-timer1"
> +
> +Clocks required for compatible = "ezchip,nps400-timer1":
> +- clocks : Must contain a single entry describing the clock input
> +
> +Example:
> +
> +timer {
> +	compatible = "ezchip,nps400-timer1";
> +	clocks = <&sysclk>;
> +};
> diff --git a/drivers/clocksource/timer-nps.c b/drivers/clocksource/timer-nps.c
> index eeef9e9..ed4bce4 100644
> --- a/drivers/clocksource/timer-nps.c
> +++ b/drivers/clocksource/timer-nps.c
> @@ -109,3 +109,216 @@ static int __init nps_setup_clocksource(struct device_node *node)
>  
>  CLOCKSOURCE_OF_DECLARE(ezchip_nps400_clksrc, "ezchip,nps400-timer",
>  		       nps_setup_clocksource);
> +CLOCKSOURCE_OF_DECLARE(ezchip_nps400_clk_src, "ezchip,nps400-timer1",
> +		       nps_setup_clocksource);
> +
> +#ifdef CONFIG_EZNPS_MTM_EXT
> +#include <soc/nps/mtm.h>
> +
> +/* Timer related Aux registers */
> +#define NPS_REG_TIMER0_TSI	0xFFFFF850
> +#define NPS_REG_TIMER0_LIMIT	0x23
> +#define NPS_REG_TIMER0_CTRL	0x22
> +#define NPS_REG_TIMER0_CNT	0x21
> +
> +/*
> + * Interrupt Enabled (IE) - re-arm the timer
> + * Not Halted (NH) - is cleared when working with JTAG (for debug)
> + */
> +#define TIMER0_CTRL_IE		BIT(0)
> +#define TIMER0_CTRL_NH		BIT(1)
> +
> +static unsigned long nps_timer0_freq;
> +static unsigned long nps_timer0_irq;
> +
> +/*
> + * Arm the timer to interrupt after @cycles
> + */
> +static void nps_clkevent_timer_event_setup(unsigned int cycles)
> +{
> +	write_aux_reg(NPS_REG_TIMER0_LIMIT, cycles);
> +	write_aux_reg(NPS_REG_TIMER0_CNT, 0);
> +
> +	write_aux_reg(NPS_REG_TIMER0_CTRL, TIMER0_CTRL_IE | TIMER0_CTRL_NH);
> +}
> +
> +/*
> + * Clear from TSI the bit for this thread (if not in periodic mode)
> + * If still there are pending HW treads set next timer event

s/treads/threads/

> + */
> +static void nps_clkevent_rm_thread(bool remove_thread)
> +{
> +	unsigned int cflags;
> +	unsigned int enabled_threads = 0;
> +	int thread;
> +
> +	hw_schd_save(&cflags);

I'm not used with hardware scheduling. Can you explain why this is needed
here ? What window race we want to close ?

> +
> +	enabled_threads = read_aux_reg(NPS_REG_TIMER0_TSI);
> +
> +	/* remove thread from TSI1 */
> +	if (remove_thread) {
> +		thread = read_aux_reg(CTOP_AUX_THREAD_ID);
> +		enabled_threads &= ~(1 << thread);
> +		write_aux_reg(NPS_REG_TIMER0_TSI, enabled_threads);
> +	}
> +
> +	/* Re-arm the timer if needed */
> +	if (!enabled_threads)
> +		write_aux_reg(NPS_REG_TIMER0_CTRL, TIMER0_CTRL_NH);
> +	else
> +		write_aux_reg(NPS_REG_TIMER0_CTRL,
> +			      TIMER0_CTRL_IE | TIMER0_CTRL_NH);
> +
> +	hw_schd_restore(cflags);
> +}
> +
> +static void nps_clkevent_add_thread(bool set_event)
> +{
> +	int thread;
> +	unsigned int cflags, enabled_threads;
> +
> +	hw_schd_save(&cflags);
> +
> +	/* add thread to TSI1 */
> +	thread = read_aux_reg(CTOP_AUX_THREAD_ID);
> +	enabled_threads = read_aux_reg(NPS_REG_TIMER0_TSI);
> +	enabled_threads |= (1 << thread);
> +	write_aux_reg(NPS_REG_TIMER0_TSI, enabled_threads);
> +
> +	/* set next timer event */
> +	if (set_event)
> +		write_aux_reg(NPS_REG_TIMER0_CTRL,
> +			      TIMER0_CTRL_IE | TIMER0_CTRL_NH);
> +
> +	hw_schd_restore(cflags);
> +}

Not sure the boolean parameters for *_rm_thread and *_add_thread helps
to clarify the code. Depending on the race window with hw_schd_save/restore
We should be able to simplify it.

> +static int nps_clkevent_set_next_event(unsigned long delta,
> +				       struct clock_event_device *dev)
> +{
> +	nps_clkevent_add_thread(true);
> +	enable_percpu_irq(nps_timer0_irq, IRQ_TYPE_NONE);
> +
> +	return 0;
> +}
> +
> +/*
> + * Whenever anyone tries to change modes, we just mask interrupts
> + * and wait for the next event to get set.
> + */
> +static int nps_clkevent_timer_shutdown(struct clock_event_device *dev)
> +{
> +	disable_percpu_irq(nps_timer0_irq);
> +
> +	return 0;
> +}
> +
> +/*
> + * For each HW thread set its relevant bit at the TSI register
> + * To arm the timer only thread 0 is needed since it is shared
> + * by all HW threads within same core.
> + */
> +static int nps_clkevent_set_periodic(struct clock_event_device *dev)
> +{
> +	nps_clkevent_add_thread(false);
> +	if (read_aux_reg(CTOP_AUX_THREAD_ID) == 0)
> +		nps_clkevent_timer_event_setup(nps_timer0_freq / HZ);
> +
> +	return 0;
> +}
> +
> +static int nps_clkevent_set_oneshot(struct clock_event_device *dev)
> +{
> +	nps_clkevent_rm_thread(true);
> +	nps_clkevent_timer_shutdown(dev);
> +
> +	return 0;
> +}
> +
> +static DEFINE_PER_CPU(struct clock_event_device, nps_clockevent_device) = {
> +	.name				=	"NPS Timer0",
> +	.features			=	CLOCK_EVT_FEAT_ONESHOT |
> +						CLOCK_EVT_FEAT_PERIODIC,
> +	.rating				=	300,
> +	.set_next_event			=	nps_clkevent_set_next_event,
> +	.set_state_periodic		=	nps_clkevent_set_periodic,
> +	.set_state_oneshot		=	nps_clkevent_set_oneshot,
> +	.set_state_oneshot_stopped	=	nps_clkevent_timer_shutdown,
> +	.set_state_shutdown		=	nps_clkevent_timer_shutdown,

Doesn't set_state_shutdown and set_state_oneshot_stopped need to remove
the HW thread from the TSI ?

> +	.tick_resume			=	nps_clkevent_timer_shutdown,
> +};
> +
> +static irqreturn_t timer_irq_handler(int irq, void *dev_id)
> +{
> +	struct clock_event_device *evt = dev_id;
> +	int irq_reenable = clockevent_state_periodic(evt);
> +
> +	/* Remove HW thread from TSI only if NOT in periodic state */
> +	nps_clkevent_rm_thread(!irq_reenable);
> +
> +	evt->event_handler(evt);
> +
> +	return IRQ_HANDLED;
> +}
> +
> +static int nps_timer_starting_cpu(unsigned int cpu)
> +{
> +	struct clock_event_device *evt = this_cpu_ptr(&nps_clockevent_device);
> +
> +	evt->cpumask = cpumask_of(smp_processor_id());
> +
> +	clockevents_config_and_register(evt, nps_timer0_freq, 0, ULONG_MAX);
> +	enable_percpu_irq(nps_timer0_irq, IRQ_TYPE_NONE);
> +
> +	return 0;
> +}
> +
> +static int nps_timer_dying_cpu(unsigned int cpu)
> +{
> +	disable_percpu_irq(nps_timer0_irq);
> +	return 0;
> +}
> +
> +static int __init nps_setup_clockevent(struct device_node *node)
> +{
> +	struct clk *clk;
> +	int ret;
> +
> +	nps_timer0_irq = irq_of_parse_and_map(node, 0);
> +	if (nps_timer0_irq <= 0) {
> +		pr_err("clockevent: missing irq");
> +		return -EINVAL;
> +	}
> +
> +	ret = nps_get_timer_clk(node, &nps_timer0_freq, &clk);
> +	if (ret)
> +		return ret;
> +
> +	/* Needs apriori irq_set_percpu_devid() done in intc map function */
> +	ret = request_percpu_irq(nps_timer0_irq, timer_irq_handler,
> +				 "Timer0 (per-cpu-tick)",
> +				 &nps_clockevent_device);
> +	if (ret) {
> +		pr_err("Couldn't request irq\n");
> +		clk_disable_unprepare(clk);
> +		return ret;
> +	}
> +
> +	ret = cpuhp_setup_state(CPUHP_AP_ARC_TIMER_STARTING,
> +				"clockevents/nps:starting",
> +				nps_timer_starting_cpu,
> +				nps_timer_dying_cpu);
> +	if (ret) {
> +		pr_err("Failed to setup hotplug state");
> +		clk_disable_unprepare(clk);
> +		free_percpu_irq(nps_timer0_irq, &nps_clockevent_device);
> +		return ret;
> +	}
> +
> +	return 0;



> +}
> +
> +CLOCKSOURCE_OF_DECLARE(ezchip_nps400_clk_evt, "ezchip,nps400-timer0",
> +		       nps_setup_clockevent);
> +#endif /* CONFIG_EZNPS_MTM_EXT */
> -- 
> 1.7.1
> 

-- 

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