On 24/02/2016 at 17:04:42 +0100, Romain Izard wrote :
> Register the counter of the Periodic Interval Timer as a possible source
> for sched_clock. Keep the timer running even if the related clockevent
> is disabled.
>
> This provides a better precision than the jiffies-based default. The
> TCB clocksource does not work, as it is registered too late in the
> initialization sequence.
>
> Signed-off-by: Romain Izard <romain.izard....@gmail.com>
> ---
> Changelog:
> v2:
> - Keep the tick counter updated when the clocksource is disabled
> - Ensure that sched_clock is a 64 bit counter
>
> drivers/clocksource/timer-atmel-pit.c | 31 ++++++++++++++++---------------
> 1 file changed, 16 insertions(+), 15 deletions(-)
>
> diff --git a/drivers/clocksource/timer-atmel-pit.c
> b/drivers/clocksource/timer-atmel-pit.c
> index d911c5dca8f1..609892bbf9da 100644
> --- a/drivers/clocksource/timer-atmel-pit.c
> +++ b/drivers/clocksource/timer-atmel-pit.c
> @@ -21,6 +21,7 @@
> #include <linux/of_address.h>
> #include <linux/of_irq.h>
> #include <linux/slab.h>
> +#include <linux/sched_clock.h>
>
> #define AT91_PIT_MR 0x00 /* Mode Register */
> #define AT91_PIT_PITIEN BIT(25) /*
> Timer Interrupt Enable */
> @@ -44,7 +45,7 @@ struct pit_data {
>
> void __iomem *base;
> u32 cycle;
> - u32 cnt;
> + u64 cnt;
> unsigned int irq;
> struct clk *mck;
> };
> @@ -77,7 +78,7 @@ static cycle_t read_pit_clk(struct clocksource *cs)
> {
> struct pit_data *data = clksrc_to_pit_data(cs);
> unsigned long flags;
> - u32 elapsed;
> + u64 elapsed;
> u32 t;
>
> raw_local_irq_save(flags);
> @@ -90,15 +91,6 @@ static cycle_t read_pit_clk(struct clocksource *cs)
> return elapsed;
> }
>
> -static int pit_clkevt_shutdown(struct clock_event_device *dev)
> -{
> - struct pit_data *data = clkevt_to_pit_data(dev);
> -
> - /* disable irq, leaving the clocksource active */
> - pit_write(data->base, AT91_PIT_MR, (data->cycle - 1) | AT91_PIT_PITEN);
> - return 0;
> -}
> -
What about preempt-rt where really we want to disable the pit?
> /*
> * Clockevent device: interrupts every 1/HZ (== pit_cycles * MCK/16)
> */
> @@ -156,15 +148,15 @@ static irqreturn_t at91sam926x_pit_interrupt(int irq,
> void *dev_id)
> WARN_ON_ONCE(!irqs_disabled());
>
> /* The PIT interrupt may be disabled, and is shared */
> - if (clockevent_state_periodic(&data->clkevt) &&
> - (pit_read(data->base, AT91_PIT_SR) & AT91_PIT_PITS)) {
> + if (pit_read(data->base, AT91_PIT_SR) & AT91_PIT_PITS) {
> unsigned nr_ticks;
>
> /* Get number of ticks performed before irq, and ack it */
> nr_ticks = PIT_PICNT(pit_read(data->base, AT91_PIT_PIVR));
> do {
> data->cnt += data->cycle;
> - data->clkevt.event_handler(&data->clkevt);
> + if (clockevent_state_periodic(&data->clkevt))
> + data->clkevt.event_handler(&data->clkevt);
> nr_ticks--;
> } while (nr_ticks);
>
> @@ -174,6 +166,13 @@ static irqreturn_t at91sam926x_pit_interrupt(int irq,
> void *dev_id)
> return IRQ_NONE;
> }
>
> +static struct clocksource *pit_sched_clock;
> +
> +static u64 pit_sched_clock_read(void)
> +{
> + return read_pit_clk(pit_sched_clock);
> +}
> +
> /*
> * Set up both clocksource and clockevent support.
> */
> @@ -206,6 +205,9 @@ static void __init at91sam926x_pit_common_init(struct
> pit_data *data)
> data->clksrc.flags = CLOCK_SOURCE_IS_CONTINUOUS;
> clocksource_register_hz(&data->clksrc, pit_rate);
>
> + pit_sched_clock = &data->clksrc;
> + sched_clock_register(pit_sched_clock_read, bits, pit_rate);
> +
> /* Set up irq handler */
> ret = request_irq(data->irq, at91sam926x_pit_interrupt,
> IRQF_SHARED | IRQF_TIMER | IRQF_IRQPOLL,
> @@ -221,7 +223,6 @@ static void __init at91sam926x_pit_common_init(struct
> pit_data *data)
> data->clkevt.rating = 100;
> data->clkevt.cpumask = cpumask_of(0);
>
> - data->clkevt.set_state_shutdown = pit_clkevt_shutdown;
> data->clkevt.set_state_periodic = pit_clkevt_set_periodic;
> data->clkevt.resume = at91sam926x_pit_resume;
> data->clkevt.suspend = at91sam926x_pit_suspend;
> --
> 2.5.0
>
--
Alexandre Belloni, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com
