[PATCH v8 4/6] clocksource: stm32: only use 32 bits timers

[Daniel Lezcano]

On 08/12/2017 10:25, Benjamin Gaignard wrote:
> 2017-12-08 9:34 GMT+01:00 Daniel Lezcano <daniel.lezcano at 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
>>
>> 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.



> I will change the wording in v9
> 
>>
>>> Signed-off-by: Benjamin Gaignard <benjamin.gaignard at 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;
>>>       }
>>
>> 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.
>>
>>
>>
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