Messages in this thread | | | Date | Wed, 24 Feb 2016 17:15:08 +0100 | From | Alexandre Belloni <> | Subject | Re: [PATCH v2] clocksource: atmel-pit: register as a sched_clock |
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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.pro@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
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