[RESEND PATCH v3] clocksource: exynos_mct: Add the support for Exynos 64bit SoC

[Chanwoo Choi]

Hi Mark,

On Thu, Jan 15, 2015 at 8:29 PM, Mark Rutland <mark.rutland at arm.com> wrote:
> On Wed, Jan 14, 2015 at 11:57:00PM +0000, Chanwoo Choi wrote:
>> Hi Kukjin,
>>
>> On 01/15/2015 01:02 AM, Daniel Lezcano wrote:
>> > On 01/14/2015 04:51 PM, Kukjin Kim wrote:
>> >> On 01/14/15 14:33, Chanwoo Choi wrote:
>> >>
>> >> Hi,
>> >>
>> >> + Doug, Olof
>> >>
>> >>> This patch adds the support for Exynos 64bit SoC. The delay_timer is only used
>> >>> for Exynos 32bit SoC.
>> >>>
>> >> Yes, the Exynos MCT(Multi-Core Timer) is 64bit timer and it is available
>> >> on 64bit exynos SoC such as exynos7. But basically ARMv8 architecture is
>> >> including ARM ARCH timer (ARM Generic Timer) and exynos7 also has
>> >> implemented it and additionally its access is faster than using memory
>> >> mapped register called SFR for MCT...so Doug submitted patch to use MCT
>> >> on 32bit exynos SoCs before.
>>
>> I know arch_timer. As you comment, ARCH timer would be used for system timer for ARMv8.
>> But, Exynos5433/Exynos7 (ARMv8) include MCT (Multi-Core Timer) IP. I checked it on
>> Exynos5433/EXynos7 User-manaual and tested it.
>>
>> I think that exynos_mct.c should support the Exynos 64-bit SoC
>> because Exynos5433/Exynos7 include already MCT (Multi-Core Timer) IP.
>>
>> Also, I have a problem to verify ARCH timer on Exynos SoC. Exynos User-manual never includes
>> the detailed information about for ARCH timer(e.g, clock for ARCH timer). I knew that
>> I can get the document of ARCH timer for ARM official site but I think it is insufficient
>> to implement ARCH timer on Exynos SoC.
>
> What do you mean by "insufficient to implement ARCH timer"?

As I knew, timer must need the source clock. The clock for ARCH timer
has dependency on Exynos SoC, But I cannot find

>
> The architected timer is mandatory in ARMv8, and required by the arm64
> kernel.
>
> Additional timers may be requried if you want to put all CPUs into low
> power states where the timer logic may be disabled and/or lose state,
> but regardless the architected timers are necessary.
>
> Thanks,
> Mark.
>
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