linux-kernel - Re: [PATCH 1/3] clocksource: davinci: work around a clocksource problem on dm365 SoC

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Date:   Tue, 17 Dec 2019 11:01:28 -0600
From:   David Lechner <david@...hnology.com>
To:     Bartosz Golaszewski <brgl@...ev.pl>
Cc:     Sekhar Nori <nsekhar@...com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Kevin Hilman <khilman@...nel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>
Subject: Re: [PATCH 1/3] clocksource: davinci: work around a clocksource
 problem on dm365 SoC

On 12/17/19 2:00 AM, Bartosz Golaszewski wrote:
> pon., 16 gru 2019 o 18:58 David Lechner <david@...hnology.com> napisał(a):
>>
>>>
>>> +static unsigned int davinci_clocksource_tim32_mode;
>>
>> static unsigned bool davinci_clocksource_initialized;
>>
>>> +
>>>    static struct davinci_clockevent *
>>>    to_davinci_clockevent(struct clock_event_device *clockevent)
>>>    {
>>> @@ -94,7 +96,7 @@ static void davinci_tim12_shutdown(void __iomem *base)
>>>         * halves. In this case TIM34 runs in periodic mode and we must
>>>         * not modify it.
>>>         */
>>> -     tcr |= DAVINCI_TIMER_ENAMODE_PERIODIC <<
>>> +     tcr |= davinci_clocksource_tim32_mode <<
>>>                DAVINCI_TIMER_ENAMODE_SHIFT_TIM34;
>>
>>          if (davinci_clocksource_initialized)
>>                  tcr |= DAVINCI_TIMER_ENAMODE_PERIODIC <<
>>                          DAVINCI_TIMER_ENAMODE_SHIFT_TIM34;
> 
> I thought about doing this initially, but then figured this code would
> be called a lot, so why not avoid branching and just store the right
> value? Alternatively we can do:
> 
>      if (likely(davinci_clocksource_initialized)
>          ....
> 

Unless there is a measurable performance difference, I think it
would be better with if/likely.