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

amit daniel kachhap
2014-06-19T11:00:26Z

On Thu, Jun 19, 2014 at 4:00 PM, Daniel Lezcano
<daniel.lezcano@linaro.org> wrote:
> On 06/19/2014 12:21 PM, amit daniel kachhap wrote:
>>
>> 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?
>
>
> AFAIU, Doug may change the exynos4_frc_read to be 32 bits. So may not need
> those macros as 'exynos4_frc_read' could be used instead.
right, its better to wait till those patches are out.
>
> Doug may confirm this.
>
>
>>>> 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?
>
>
> No problem with the naming. As Tomasz pointed also, you are passing '&' for
> the function pointer.
yes my mistake.
>
>
>>>> + 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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>
>
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