linux-kernel - [PATCH v9 2/6] clocksource: stm32: increase min delta value

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Date:   Fri,  8 Dec 2017 12:32:46 +0100
From:   Benjamin Gaignard <benjamin.gaignard@...aro.org>
To:     robh+dt@...nel.org, mark.rutland@....com, linux@...linux.org.uk,
        mcoquelin.stm32@...il.com, alexandre.torgue@...com,
        daniel.lezcano@...aro.org, tglx@...utronix.de, arnd@...db.de
Cc:     devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org,
        Benjamin Gaignard <benjamin.gaignard@...aro.org>
Subject: [PATCH v9 2/6] clocksource: stm32: increase min delta value

From: Benjamin Gaignard <benjamin.gaignard@...aro.org>

The CPU is a CortexM4 @ 200MHZ and the clocks driving
the timers are at 90MHZ with a min delta at 1 you could
have an interrupt each 0.01 ms which is really to much.
By increase it to 0x60 it give more time (around 1 ms)
to CPU to handle the interrupt.

Signed-off-by: Benjamin Gaignard <benjamin.gaignard@...aro.org>
---
 drivers/clocksource/timer-stm32.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/drivers/clocksource/timer-stm32.c b/drivers/clocksource/timer-stm32.c
index fc61fd18a182..a45f1f1cd040 100644
--- a/drivers/clocksource/timer-stm32.c
+++ b/drivers/clocksource/timer-stm32.c
@@ -36,6 +36,12 @@
 
 #define TIM_EGR_UG	BIT(0)
 
+/*
+ * The clock driving the hardware is at 90MHZ with a MIN_DELTA
+ * at 0x60 it gives around 1 ms to the CPU to handle the interrupt
+ */
+#define MIN_DELTA	0x60
+
 static int stm32_clock_event_shutdown(struct clock_event_device *evt)
 {
 	struct timer_of *to = to_timer_of(evt);
@@ -129,7 +135,8 @@ static int __init stm32_clockevent_init(struct device_node *node)
 	writel_relaxed(0, timer_of_base(to) + TIM_SR);
 
 	clockevents_config_and_register(&to->clkevt,
-					timer_of_period(to), 0x1, max_delta);
+					timer_of_period(to),
+					MIN_DELTA, max_delta);
 
 	pr_info("%pOF: STM32 clockevent driver initialized (%d bits)\n",
 			node, bits);
-- 
2.15.0