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Date: Thu, 7 Dec 2017 17:49:55 +0100 From: Daniel Lezcano <daniel.lezcano@...aro.org> To: Benjamin Gaignard <benjamin.gaignard@...aro.org> Cc: Rob Herring <robh+dt@...nel.org>, Mark Rutland <mark.rutland@....com>, Russell King - ARM Linux <linux@...linux.org.uk>, Maxime Coquelin <mcoquelin.stm32@...il.com>, Alexandre Torgue <alexandre.torgue@...com>, Thomas Gleixner <tglx@...utronix.de>, Ludovic Barre <ludovic.barre@...com>, Julien Thierry <julien.thierry@....com>, Sudeep Holla <sudeep.holla@....com>, Arnd Bergmann <arnd@...db.de>, devicetree@...r.kernel.org, Linux ARM <linux-arm-kernel@...ts.infradead.org>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org> Subject: Re: [PATCH v8 4/6] clocksource: stm32: only use 32 bits timers On 07/12/2017 17:33, Benjamin Gaignard wrote: > 2017-12-07 16:27 GMT+01:00 Daniel Lezcano <daniel.lezcano@...aro.org>: >> On 14/11/2017 09:52, Benjamin Gaignard wrote: >>> The clock driving counters is at 90MHz so the maximum period >>> for 16 bis counters is around 750 ms which is a short period >>> for a clocksource. >> >> Isn't it 728us ? > > yes it is: 2^16 / 90.000.000 => 728us Ok, now I can do the connection with the previous patch. So, the real issue of all this is the 16bits clocksource is wrapping up every 728us, hence the clockevent periodically expires every ~728us to keep the timekeeping consistent. Unfortunately, the kernel has a too high overhead for this as the system is consistently processing this timer leading to a CPU time resource starvation. Is that correct ? >>> For 32 bits counters this period is close >>> 47 secondes which is more acceptable. >>> >>> This patch remove 16 bits counters support and makes sure that >>> they won't be probed anymore. >>> >>> Signed-off-by: Benjamin Gaignard <benjamin.gaignard@...aro.org> >>> --- >>> drivers/clocksource/timer-stm32.c | 26 ++++++++++++-------------- >>> 1 file changed, 12 insertions(+), 14 deletions(-) >>> >>> diff --git a/drivers/clocksource/timer-stm32.c b/drivers/clocksource/timer-stm32.c >>> index ae41a19..8173bcf 100644 >>> --- a/drivers/clocksource/timer-stm32.c >>> +++ b/drivers/clocksource/timer-stm32.c >>> @@ -83,9 +83,9 @@ static irqreturn_t stm32_clock_event_handler(int irq, void *dev_id) >>> static int __init stm32_clockevent_init(struct device_node *node) >>> { >>> struct reset_control *rstc; >>> - unsigned long max_delta; >>> - int ret, bits, prescaler = 1; >>> + unsigned long max_arr; >>> struct timer_of *to; >>> + int ret; >>> >>> to = kzalloc(sizeof(*to), GFP_KERNEL); >>> if (!to) >>> @@ -115,29 +115,27 @@ static int __init stm32_clockevent_init(struct device_node *node) >>> >>> /* Detect whether the timer is 16 or 32 bits */ >>> writel_relaxed(~0U, timer_of_base(to) + TIM_ARR); >>> - max_delta = readl_relaxed(timer_of_base(to) + TIM_ARR); >>> - if (max_delta == ~0U) { >>> - prescaler = 1; >>> - bits = 32; >>> - } else { >>> - prescaler = 1024; >>> - bits = 16; >>> + max_arr = readl_relaxed(timer_of_base(to) + TIM_ARR); >>> + if (max_arr != ~0U) { >>> + pr_err("32 bits timer is needed\n"); >>> + ret = -EINVAL; >>> + goto deinit; >>> } >>> + >>> writel_relaxed(0, timer_of_base(to) + TIM_ARR); >>> >>> - writel_relaxed(prescaler - 1, timer_of_base(to) + TIM_PSC); >>> + 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); >>> >>> clockevents_config_and_register(&to->clkevt, >>> - timer_of_period(to), MIN_DELTA, max_delta); >>> - >>> - pr_info("%pOF: STM32 clockevent driver initialized (%d bits)\n", >>> - node, bits); >>> + timer_of_period(to), MIN_DELTA, ~0U); >>> >>> return 0; >>> >>> +deinit: >>> + timer_of_exit(to); >>> err: >>> kfree(to); >>> return ret; >>> >> >> >> -- >> <http://www.linaro.org/> Linaro.org │ Open source software for ARM SoCs >> >> Follow Linaro: <http://www.facebook.com/pages/Linaro> Facebook | >> <http://twitter.com/#!/linaroorg> Twitter | >> <http://www.linaro.org/linaro-blog/> Blog >> > > > -- <http://www.linaro.org/> Linaro.org │ Open source software for ARM SoCs Follow Linaro: <http://www.facebook.com/pages/Linaro> Facebook | <http://twitter.com/#!/linaroorg> Twitter | <http://www.linaro.org/linaro-blog/> Blog
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