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

amit daniel kachhap
2014-06-19T10:22:00Z

On Thu, Jun 19, 2014 at 2:41 PM, Daniel Lezcano
<daniel.lezcano@linaro.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@samsung.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);
>>
>>
>
>
> --
> <http://www.linaro.org/> Linaro.org │ Open source software for ARM SoCs
>
> Follow Linaro: <http://www.facebook.com/pages/Linaro> Facebook |
> <http://twitter.com/#!/linaroorg> Twitter |
> <http://www.linaro.org/linaro-blog/> Blog
>
> --
> To unsubscribe from this list: send the line "unsubscribe linux-samsung-soc"
> in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at http://vger.kernel.org/majordomo-info.html