linux-kernel - Re: [PATCH v2 3/6] clocksource/drivers/tegra: Set and use timer's period

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Message-ID: <b92383e6-31e4-0797-1e7a-76410ebfba6c@nvidia.com>
Date:   Tue, 18 Jun 2019 09:40:25 +0100
From:   Jon Hunter <jonathanh@...dia.com>
To:     Dmitry Osipenko <digetx@...il.com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Joseph Lo <josephl@...dia.com>,
        Thierry Reding <thierry.reding@...il.com>,
        Peter De Schrijver <pdeschrijver@...dia.com>
CC:     <linux-tegra@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 3/6] clocksource/drivers/tegra: Set and use timer's
 period


On 17/06/2019 15:04, Dmitry Osipenko wrote:
> 17.06.2019 13:51, Jon Hunter пишет:
>>
>> On 14/06/2019 17:45, Dmitry Osipenko wrote:
>>> 14.06.2019 18:48, Jon Hunter пишет:
>>>>
>>>> On 10/06/2019 17:43, Dmitry Osipenko wrote:
>>>>> The of_clk structure has a period field that is set up initially by
>>>>> timer_of_clk_init(), that period value need to be adjusted for a case of
>>>>> TIMER1-9 that are running at a fixed rate that doesn't match the clock's
>>>>> rate. Note that the period value is currently used only by some of the
>>>>> clocksource drivers internally and hence this is just a minor cleanup
>>>>> change that doesn't fix anything.
>>>>>
>>>>> Signed-off-by: Dmitry Osipenko <digetx@...il.com>
>>>>> ---
>>>>>  drivers/clocksource/timer-tegra.c | 5 +++--
>>>>>  1 file changed, 3 insertions(+), 2 deletions(-)
>>>>>
>>>>> diff --git a/drivers/clocksource/timer-tegra.c b/drivers/clocksource/timer-tegra.c
>>>>> index 810b4e7435cf..646b3530c2d2 100644
>>>>> --- a/drivers/clocksource/timer-tegra.c
>>>>> +++ b/drivers/clocksource/timer-tegra.c
>>>>> @@ -71,9 +71,9 @@ static int tegra_timer_shutdown(struct clock_event_device *evt)
>>>>>  static int tegra_timer_set_periodic(struct clock_event_device *evt)
>>>>>  {
>>>>>  	void __iomem *reg_base = timer_of_base(to_timer_of(evt));
>>>>> +	unsigned long period = timer_of_period(to_timer_of(evt));
>>>>>  
>>>>> -	writel_relaxed(TIMER_PTV_EN | TIMER_PTV_PER |
>>>>> -		       ((timer_of_rate(to_timer_of(evt)) / HZ) - 1),
>>>>> +	writel_relaxed(TIMER_PTV_EN | TIMER_PTV_PER | (period - 1),
>>>>>  		       reg_base + TIMER_PTV);
>>>>>  
>>>>>  	return 0;
>>>>> @@ -297,6 +297,7 @@ static int __init tegra_init_timer(struct device_node *np, bool tegra20,
>>>>>  		cpu_to->clkevt.rating = rating;
>>>>>  		cpu_to->clkevt.cpumask = cpumask_of(cpu);
>>>>>  		cpu_to->of_base.base = timer_reg_base + base;
>>>>> +		cpu_to->of_clk.period = DIV_ROUND_UP(rate, HZ);
>>>>
>>>> Any reason you made this a round-up?
>>>
>>> That's what timer_of_clk_init() does, I assume it should be a more correct variant.
>>
>> Sounds to me like this should be 2 patches, because you are changing the
>> value. This is not just purely cleanup IMO.
> 
> Indeed, that could be at least mentioned in the commit message. Probably I just
> assumed that this is such a minor change that not worth anything. A hundred of
> microseconds is hardly noticeable.
> 
> I'm not really sure if this really worth a re-spin at this point. Jon, are you insisting?

At a minimum the changelog needs to be udpated to reflect what is going
on here. Yes it may not be a massive difference, but I prefer not to
change things without any rationale.

Cheers
Jon

-- 
nvpublic