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Subject[PATCH v8 5/6] clocksource: stm32: add clocksource support
Date
The stm32 timer hardware is currently only used as a clock event device,
but it can be utilized as a clocksource as well.

Implement this by enabling the free running counter in the hardware block
and converting the clock event part from a count down event timer to a
comparator based timer.

Signed-off-by: Benjamin Gaignard <benjamin.gaignard@linaro.org>
---
drivers/clocksource/timer-stm32.c | 116 +++++++++++++++++++++++++++++---------
1 file changed, 88 insertions(+), 28 deletions(-)

diff --git a/drivers/clocksource/timer-stm32.c b/drivers/clocksource/timer-stm32.c
index 8173bcf..c0a62cd 100644
--- a/drivers/clocksource/timer-stm32.c
+++ b/drivers/clocksource/timer-stm32.c
@@ -16,6 +16,8 @@
#include <linux/of_irq.h>
#include <linux/clk.h>
#include <linux/reset.h>
+#include <linux/sched_clock.h>
+#include <linux/slab.h>

#include "timer-of.h"

@@ -23,16 +25,16 @@
#define TIM_DIER 0x0c
#define TIM_SR 0x10
#define TIM_EGR 0x14
+#define TIM_CNT 0x24
#define TIM_PSC 0x28
#define TIM_ARR 0x2c
+#define TIM_CCR1 0x34

#define TIM_CR1_CEN BIT(0)
-#define TIM_CR1_OPM BIT(3)
+#define TIM_CR1_UDIS BIT(1)
#define TIM_CR1_ARPE BIT(7)

-#define TIM_DIER_UIE BIT(0)
-
-#define TIM_SR_UIF BIT(0)
+#define TIM_DIER_CC1IE BIT(1)

#define TIM_EGR_UG BIT(0)

@@ -42,28 +44,44 @@ static int stm32_clock_event_shutdown(struct clock_event_device *evt)
{
struct timer_of *to = to_timer_of(evt);

- writel_relaxed(0, timer_of_base(to) + TIM_CR1);
+ writel_relaxed(0, timer_of_base(to) + TIM_DIER);
+
return 0;
}

-static int stm32_clock_event_set_periodic(struct clock_event_device *evt)
+static int stm32_clock_event_set_next_event(unsigned long evt,
+ struct clock_event_device *clkevt)
{
- struct timer_of *to = to_timer_of(evt);
+ struct timer_of *to = to_timer_of(clkevt);
+ unsigned long now, next;

- writel_relaxed(timer_of_period(to), timer_of_base(to) + TIM_ARR);
- writel_relaxed(TIM_CR1_ARPE | TIM_CR1_CEN, timer_of_base(to) + TIM_CR1);
+ next = readl_relaxed(timer_of_base(to) + TIM_CNT) + evt;
+ writel_relaxed(next, timer_of_base(to) + TIM_CCR1);
+ now = readl_relaxed(timer_of_base(to) + TIM_CNT);
+
+ if ((next - now) > evt)
+ return -ETIME;
+
+ writel_relaxed(TIM_DIER_CC1IE, timer_of_base(to) + TIM_DIER);

return 0;
}

-static int stm32_clock_event_set_next_event(unsigned long evt,
- struct clock_event_device *clkevt)
+static int stm32_clock_event_set_periodic(struct clock_event_device *evt)
{
- struct timer_of *to = to_timer_of(clkevt);
+ struct timer_of *to = to_timer_of(evt);

- writel_relaxed(evt, timer_of_base(to) + TIM_ARR);
- writel_relaxed(TIM_CR1_ARPE | TIM_CR1_OPM | TIM_CR1_CEN,
- timer_of_base(to) + TIM_CR1);
+ return stm32_clock_event_set_next_event(timer_of_period(to), evt);
+}
+
+static int stm32_clock_event_set_oneshot(struct clock_event_device *evt)
+{
+ struct timer_of *to = to_timer_of(evt);
+ unsigned long val;
+
+ val = readl_relaxed(timer_of_base(to) + TIM_CNT);
+ writel_relaxed(val, timer_of_base(to) + TIM_CCR1);
+ writel_relaxed(TIM_DIER_CC1IE, timer_of_base(to) + TIM_DIER);

return 0;
}
@@ -75,12 +93,57 @@ static irqreturn_t stm32_clock_event_handler(int irq, void *dev_id)

writel_relaxed(0, timer_of_base(to) + TIM_SR);

+ if (clockevent_state_periodic(evt))
+ stm32_clock_event_set_periodic(evt);
+ else
+ stm32_clock_event_shutdown(evt);
+
evt->event_handler(evt);

return IRQ_HANDLED;
}

-static int __init stm32_clockevent_init(struct device_node *node)
+static void __init stm32_clockevent_init(struct timer_of *to)
+{
+ writel_relaxed(0, timer_of_base(to) + TIM_DIER);
+ writel_relaxed(0, timer_of_base(to) + TIM_SR);
+
+ clockevents_config_and_register(&to->clkevt,
+ timer_of_rate(to), MIN_DELTA, ~0U);
+}
+
+static void __iomem *stm32_timer_cnt __read_mostly;
+static u64 notrace stm32_read_sched_clock(void)
+{
+ return readl_relaxed(stm32_timer_cnt);
+}
+
+static int __init stm32_clocksource_init(struct timer_of *to)
+{
+ writel_relaxed(~0U, timer_of_base(to) + TIM_ARR);
+ writel_relaxed(0, timer_of_base(to) + TIM_PSC);
+ writel_relaxed(0, timer_of_base(to) + TIM_SR);
+ writel_relaxed(0, timer_of_base(to) + TIM_DIER);
+ writel_relaxed(0, timer_of_base(to) + TIM_SR);
+ writel_relaxed(TIM_CR1_ARPE | TIM_CR1_UDIS,
+ timer_of_base(to) + TIM_CR1);
+
+ /* Make sure that registers are updated */
+ writel_relaxed(TIM_EGR_UG, timer_of_base(to) + TIM_EGR);
+
+ /* Enable controller */
+ writel_relaxed(TIM_CR1_ARPE | TIM_CR1_UDIS | TIM_CR1_CEN,
+ timer_of_base(to) + TIM_CR1);
+
+ stm32_timer_cnt = timer_of_base(to) + TIM_CNT;
+ sched_clock_register(stm32_read_sched_clock, 32, timer_of_rate(to));
+
+ return clocksource_mmio_init(stm32_timer_cnt, "stm32_timer",
+ timer_of_rate(to), 250, 32,
+ clocksource_mmio_readl_up);
+}
+
+static int __init stm32_timer_init(struct device_node *node)
{
struct reset_control *rstc;
unsigned long max_arr;
@@ -92,12 +155,13 @@ static int __init stm32_clockevent_init(struct device_node *node)
return -ENOMEM;

to->flags = TIMER_OF_IRQ | TIMER_OF_CLOCK | TIMER_OF_BASE;
+
to->clkevt.name = "stm32_clockevent";
to->clkevt.rating = 200;
- to->clkevt.features = CLOCK_EVT_FEAT_PERIODIC;
+ to->clkevt.features = CLOCK_EVT_FEAT_ONESHOT | CLOCK_EVT_FEAT_PERIODIC;
to->clkevt.set_state_shutdown = stm32_clock_event_shutdown;
to->clkevt.set_state_periodic = stm32_clock_event_set_periodic;
- to->clkevt.set_state_oneshot = stm32_clock_event_shutdown;
+ to->clkevt.set_state_oneshot = stm32_clock_event_set_oneshot;
to->clkevt.tick_resume = stm32_clock_event_shutdown;
to->clkevt.set_next_event = stm32_clock_event_set_next_event;

@@ -122,23 +186,19 @@ static int __init stm32_clockevent_init(struct device_node *node)
goto deinit;
}

- writel_relaxed(0, timer_of_base(to) + TIM_ARR);
-
- writel_relaxed(0, timer_of_base(to) + TIM_PSC);
- writel_relaxed(TIM_EGR_UG, timer_of_base(to) + TIM_EGR);
- writel_relaxed(TIM_DIER_UIE, timer_of_base(to) + TIM_DIER);
- writel_relaxed(0, timer_of_base(to) + TIM_SR);
+ ret = stm32_clocksource_init(to);
+ if (ret)
+ goto deinit;

- clockevents_config_and_register(&to->clkevt,
- timer_of_period(to), MIN_DELTA, ~0U);
+ stm32_clockevent_init(to);

return 0;

deinit:
- timer_of_exit(to);
+ timer_of_cleanup(to);
err:
kfree(to);
return ret;
}

-TIMER_OF_DECLARE(stm32, "st,stm32-timer", stm32_clockevent_init);
+TIMER_OF_DECLARE(stm32, "st,stm32-timer", stm32_timer_init);
--
2.7.4
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