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Date: Fri, 8 Dec 2017 10:29:44 +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 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.
> 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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