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SubjectRe: [PATCH v8 4/6] clocksource: stm32: only use 32 bits timers
2017-12-07 17:49 GMT+01:00 Daniel Lezcano <daniel.lezcano@linaro.org>:
> On 07/12/2017 17:33, Benjamin Gaignard wrote:
>> 2017-12-07 16:27 GMT+01:00 Daniel Lezcano <daniel.lezcano@linaro.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 ?

Yes that is 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@linaro.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;
>>>>
>>>
>>>
>>> --
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>>>
>>
>>
>>
>
>
> --
> <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
>



--
Benjamin Gaignard

Graphic Study Group

Linaro.org │ Open source software for ARM SoCs

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