linux-kernel - Re: [PATCH v8 4/6] clocksource: stm32: only use 32 bits timers

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Message-ID: <CA+M3ks47fE4uo=wtoWkmp+cr8gmwWFVMWk5dYc9G5=guGU0SOQ@mail.gmail.com>
Date:   Fri, 8 Dec 2017 10:31:32 +0100
From:   Benjamin Gaignard <benjamin.gaignard@...aro.org>
To:     Daniel Lezcano <daniel.lezcano@...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

2017-12-08 10:29 GMT+01:00 Daniel Lezcano <daniel.lezcano@...aro.org>:
> On 08/12/2017 10:25, Benjamin Gaignard wrote:
>> 2017-12-08 9:34 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
>>>
>>> 728 us
>>>
>>>> which is a short period for a clocksource.
>>>
>>> Which clocksource are you talking about ?
>>>
>>>> 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.
>>>
>>> Are we talking about clockevent or clocksource?
>>>
>>> Is this issue present today ? Or is it if we add the clocksource support
>>> ? We are talking about clocksource but we change the clockevent code.
>>>
>>> All this is very confusing.
>>>
>>> I have a rough idea of what is happening, but it is not up to me to
>>> decode and infer from the changes, you need to describe *clearly* the
>>> situation.
>>>
>>>  - What happens if we use a 16bits timer as a clockevent ?
>>>  - What happens if we use a 16bits timer as a clocksource ?
>>>  - Why is it preferable to remove the support of the 16bits timers
>>> instead of downgrading them with the rating ?
>>
>> Up to this patch it is only about clockevent, clocksource code is
>> introduced in patch 5.
>> For the both cases 16bits counter have a a too short period (728us)
>> and can't be used
>> so downgrading the rating is not a solution.
>
> You have to explain why it is a too short period. I will be happy to see
> an example of the issues the user is facing.

This a very basic issue, the kernel doesn't boot at all...

>
>
>
>> I will change the wording in v9
>>
>>>
>>>> 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;
>>>>       }
>>>
>>> Wrap this in a function:
>>>
>>> static bool stm32_timer_is_32bits(struct timer_of *to)
>>> {
>>>         return readl_relaxed(timer_of_base(to) + TIM_ARR) == ~0UL;
>>> }
>>>
>>> Then clearly inform the user.
>>>
>>> if (!stm32_timer_is_32bits(to)) {
>>>         pr_warn("Timer %pOF is a 16 bits timer\n", node);
>>>         /* abort the registration or downgrade the timer's rating */
>>> }
>>
>> Ok I will change that in v9
>>
>>>
>>>> +
>>>>       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);
>>>
>>> Fix this please (timer_of_cleanup).
>>>
>>> In the future, make sure the patches are git-bisect safe.
>>>
>>>
>>>
>>> --
>>>  <http://www.linaro.org/> Linaro.org │ Open source software for ARM SoCs
>>>
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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 |
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>



-- 
Benjamin Gaignard

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