linux-kernel - Re: [PATCH v2] clocksource: exynos-mct: Register the timer for stable udelay

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Message-ID: <CADGdYn6YObHdRq6A9-L7qbD+EYiPrwhrKkLwyA5Z=0tDoWUzvA@mail.gmail.com>
Date:	Thu, 19 Jun 2014 15:51:58 +0530
From:	amit daniel kachhap <amit.daniel@...sung.com>
To:	Daniel Lezcano <daniel.lezcano@...aro.org>
Cc:	"linux-samsung-soc@...r.kernel.org" 
	<linux-samsung-soc@...r.kernel.org>,
	Kukjin Kim <kgene.kim@...sung.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	LAK <linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	David Riley <davidriley@...omium.org>,
	Doug Anderson <dianders@...omium.org>,
	Tomasz Figa <tomasz.figa@...il.com>
Subject: Re: [PATCH v2] clocksource: exynos-mct: Register the timer for stable udelay

On Thu, Jun 19, 2014 at 2:41 PM, Daniel Lezcano
<daniel.lezcano@...aro.org> wrote:
> On 06/19/2014 10:39 AM, Amit Daniel Kachhap wrote:
>>
>> This patch register the exynos mct clocksource as the current timer
>> as it has constant clock rate. This will generate correct udelay for the
>> exynos platform and avoid using unnecessary calibrated jiffies. This
>> change
>> has been tested on exynos5420 based board and udelay is very close to
>> expected.
>>
>> Signed-off-by: Amit Daniel Kachhap <amit.daniel@...sung.com>
>> ---
>> Changes in V2:
>> * Added #defines for ARM and ARM64 as pointed by Doug Anderson.
>>
>> Patches from David Riley confirmed that udelay is broken in exynos5420.
>> Link to those patches are,
>> 1) https://patchwork.kernel.org/patch/4344911/
>> 2) https://patchwork.kernel.org/patch/4344881/
>>
>>   drivers/clocksource/exynos_mct.c | 15 +++++++++++++++
>>   1 file changed, 15 insertions(+)
>>
>> diff --git a/drivers/clocksource/exynos_mct.c
>> b/drivers/clocksource/exynos_mct.c
>> index f71d55f..02927e2 100644
>> --- a/drivers/clocksource/exynos_mct.c
>> +++ b/drivers/clocksource/exynos_mct.c
>> @@ -195,10 +195,25 @@ static u64 notrace exynos4_read_sched_clock(void)
>>         return exynos4_frc_read(&mct_frc);
>>   }
>>
>> +static struct delay_timer exynos4_delay_timer;
>> +
>> +static unsigned long exynos4_read_current_timer(void)
>> +{
>> +#ifdef ARM
>> +       return __raw_readl(reg_base + EXYNOS4_MCT_G_CNT_L);
>> +#else /* ARM64, etc */
>> +       return exynos4_frc_read(&mct_frc);
>> +#endif
>> +}
>> +
>
>
> There isn't another solution than that ? macros definitions in C file are
> avoided as much as possible.
I also didn't want to use macros but used as a last option. you want
me to put more comments here?
Or something like below is also possible for checking the size of
(unsigned long) in runtime.

unsigned long x;
unsigned int size = (char *)(&x + 1) - (char *)(&x);
if (size == 4)
           return __raw_readl(reg_base + EXYNOS4_MCT_G_CNT_L);
else
           return exynos4_frc_read(&mct_frc);

But this involves extra computation which should not be used for time
critical functions.
Any suggestion?

>
>
>>   static void __init exynos4_clocksource_init(void)
>>   {
>>         exynos4_mct_frc_start();
>>
>> +       exynos4_delay_timer.read_current_timer =
>> &exynos4_read_current_timer;
>
>
> &exynos4_read_current_timer ?
Any issue in the naming?
>
>
>> +       exynos4_delay_timer.freq = clk_rate;
>> +       register_current_timer_delay(&exynos4_delay_timer);
>> +
>>         if (clocksource_register_hz(&mct_frc, clk_rate))
>>                 panic("%s: can't register clocksource\n", mct_frc.name);
>>
>>
>
>
> --
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