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

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Date:	Thu, 15 Jan 2015 21:52:38 +0900
From:	Chanwoo Choi <cwchoi00@...il.com>
To:	Mark Rutland <mark.rutland@....com>
Cc:	"linux-samsung-soc@...r.kernel.org" 
	<linux-samsung-soc@...r.kernel.org>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Doug Anderson <dianders@...omium.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"inki.dae@...sung.com" <inki.dae@...sung.com>,
	Kukjin Kim <kgene@...nel.org>, Olof Johansson <olof@...om.net>,
	Kukjin Kim <kgene.kim@...sung.com>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [RESEND PATCH v3] clocksource: exynos_mct: Add the support for
 Exynos 64bit SoC

On Thu, Jan 15, 2015 at 9:46 PM, Chanwoo Choi <cwchoi00@...il.com> wrote:
> Hi Mark,
>
> On Thu, Jan 15, 2015 at 8:29 PM, Mark Rutland <mark.rutland@....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

I'm so sorry about this mistake. I pressed the send button before
completing reply.

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

When I tried to use ARCH timer on Exynos3250, It is not working. We
can check this ARCH timer issue of Exynos3250
on following patch[1]:
[1] http://www.spinics.net/lists/arm-kernel/msg322943.html

>
>>
>> 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.

I agree that ARCH timer is mandatory.

I just think that existing exynos-mct.c driver should support the Exynos5/7 SoC
because released Exynos5/7 SoC includes already MCT IP for system timer.

Best Regards,
Chanwoo Choi
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