clocksource/drivers/stm32: Add the timer delay callback

Add the timer delay callback, that saves us ~90ms of boot time.
Tested-by: Benjamin Gaignard <benjamin.gaignard@st.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Acked-by: Benjamin Gaignard <benjamin.gaignard@st.com>
Cc: Alexandre Torgue <alexandre.torgue@st.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Maxime Coquelin <mcoquelin.stm32@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1515418139-23276-19-git-send-email-daniel.lezcano@linaro.orgSigned-off-by: Ingo Molnar <mingo@kernel.org>

drivers/clocksource/timer-stm32.c

@@ -9,6 +9,7 @@
 #include <linux/kernel.h>
 #include <linux/clocksource.h>
 #include <linux/clockchips.h>
+#include <linux/delay.h>
 #include <linux/irq.h>
 #include <linux/interrupt.h>
 #include <linux/of.h>
@@ -88,6 +89,13 @@ static u64 notrace stm32_read_sched_clock(void)
 	return readl_relaxed(stm32_timer_cnt);
 }
 
+static struct delay_timer stm32_timer_delay;
+
+static unsigned long stm32_read_delay(void)
+{
+	return readl_relaxed(stm32_timer_cnt);
+}
+
 static void stm32_clock_event_disable(struct timer_of *to)
 {
 	writel_relaxed(0, timer_of_base(to) + TIM_DIER);
@@ -230,6 +238,11 @@ static int __init stm32_clocksource_init(struct timer_of *to)
 		stm32_timer_cnt = timer_of_base(to) + TIM_CNT;
 		sched_clock_register(stm32_read_sched_clock, bits, timer_of_rate(to));
 		pr_info("%s: STM32 sched_clock registered\n", name);
+
+		stm32_timer_delay.read_current_timer = stm32_read_delay;
+		stm32_timer_delay.freq = timer_of_rate(to);
+		register_current_timer_delay(&stm32_timer_delay);
+		pr_info("%s: STM32 delay timer registered\n", name);
 	}
 
 	return clocksource_mmio_init(timer_of_base(to) + TIM_CNT, name,