From: Kukjin Kim <kgene.kim@gmail.com>
To: Krzysztof Kozlowski <krzk@kernel.org>
Cc: Olof Johansson <olof@lixom.net>, Arnd Bergmann <arnd@arndb.de>,
Kevin Hilman <khilman@kernel.org>,
"arm@kernel.org" <arm@kernel.org>,
Krzysztof Kozlowski <k.kozlowski@samsung.com>,
Kukjin Kim <kgene@kernel.org>,
"linux-arm-kernel@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>,
"linux-samsung-soc@vger.kernel.org"
<linux-samsung-soc@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>,
Javier Martinez Canillas <javier@osg.samsung.com>,
Daniel Lezcano <daniel.lezcano@linaro.org>,
kgene.kim@samsung.com
Subject: Re: [GIT PULL 1/3] ARM: soc: exynos: Drivers for v4.9
Date: Tue, 11 Oct 2016 09:46:49 +0900 [thread overview]
Message-ID: <50A42280-0A39-44E3-8E35-C24031EB4DF0@gmail.com> (raw)
In-Reply-To: <53745281-AF17-4A3A-8BB5-63EED3563298@gmail.com>
2016. 10. 3. 21:19 Kukjin Kim <kgene.kim@gmail.com> wrote:
+ my samsung email
> 2016. 10. 3. 15:48 Krzysztof Kozlowski <krzk@kernel.org> wrote:
>
>>>> On Sun, Oct 02, 2016 at 05:25:07PM -0700, Olof Johansson wrote:
>>>>> On Mon, Sep 19, 2016 at 8:53 AM, Krzysztof Kozlowski <krzk@kernel.org> wrote:
>>>>>> On Mon, Sep 19, 2016 at 05:02:40PM +0200, Arnd Bergmann wrote:
>>>>>> On Sunday, September 18, 2016 6:39:46 PM CEST Krzysztof Kozlowski wrote:
>>>>>> Samsung drivers/soc update for v4.9:
>>>>>> 1. Allow compile testing of exynos-mct clocksource driver on ARM64.
>>>>>> 2. Document Exynos5433 PMU compatible (already used by clkout driver and more
>>>>>> will be coming soon).
>>>>>
>>>>> Pulled into next/drivers, thanks
>>>>>
>>>>> Just for my understanding: why do we need the exynos-mct driver on ARM64
>>>>> but not the delay-timer portion of it?
>>>>
>>>> I think we want all of it but Doug's optimization 3252a646aa2c
>>>> ("clocksource: exynos_mct: Only use 32-bits where possible") is not
>>>> ARM64 friendly. One way of dealing with it would be to prepare two
>>>> versions of exynos4_read_current_timer(). One reading only lower 32-bit
>>>> value for ARMv7 and second (slow) reading lower and upper for ARMv8.
>>>>
>>>>>
>>>>> Is there an advantage in using MCT over the architected timer on these
>>>>> chips? If so, should we also have a way to use it as the delay timer?
>>>>
>>>> No, there is no real advantage... except that the SoC has some
>>>> interesting "characteristics"... The timers are tightly coupled. Very
>>>> tightly. I spent a lot of time and failed to boot my ARMv8 board without
>>>> some MCT magic.
>>>
>>> What kind of magic is that?
>>
>> Most notably: the arch timer starts when MCT forward running counter
>> starts. Without kicking MCT, the arch timer seems to be frozen.
>>
>>> I can understand that needing the MCT for
>>> some system-level timer functionality might be true (wakeups, etc),
>>> but for system timesource avoiding the MMIO timer and using the arch
>>> ones is a substantial performance improvement for gettimeofday() and
>>> friends.
>>>
>>> There was extensive discussion last year over using arch timers on
>>> 5420/5422, and it fizzled out with vague comments about something not
>>> working right between A15/A7 on b.L. hardware. I'm presuming whatever
>>> implementation details of that SoC has since been fixed on later chips
>>> (including v8). Any chance you can confirm? It'd be very nice to leave
>>> MCT behind on v8 as a system time source.
>>
>> Unfortunately, I cannot confirm this, at least on Exynos5433 (ARMv8). I
>> played with arch and MCT timers on it and failed to get the
>> arch-timer-only setup working. I did not have access to newer Exynos
>> designs (Exynos 7) so I do not know how it works there.
>
> Hi guys,
>
> I know what Olof want to know and actually several days ago someone asked me about that. As you guys talked, a couple of years ago there were some discussions...BTW I need to contact to hardware designer before let you guys know because something needs to be confirmed by them even I know roughly.
>
> Note I'm in vacation with my family. Will be back on this in several days with exact information.
>
> BRs,
> Kukjin
next prev parent reply other threads:[~2016-10-11 0:46 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-09-18 16:39 [GIT PULL 0/3] ARM: exynos: Second round of stuff for v4.9 Krzysztof Kozlowski
2016-09-18 16:39 ` [GIT PULL 1/3] ARM: soc: exynos: Drivers " Krzysztof Kozlowski
2016-09-19 15:02 ` Arnd Bergmann
2016-09-19 15:53 ` Krzysztof Kozlowski
2016-10-03 0:25 ` Olof Johansson
2016-10-03 7:48 ` Krzysztof Kozlowski
2016-10-03 12:19 ` Kukjin Kim
2016-10-11 0:46 ` Kukjin Kim [this message]
2016-10-11 0:58 ` Kukjin Kim
2016-09-18 16:39 ` [GIT PULL 2/3] ARM: dts: exynos: DT for v4.9, second round Krzysztof Kozlowski
2016-09-19 15:46 ` Arnd Bergmann
2016-09-18 16:39 ` [GIT PULL 3/3] ARM: dts: exynos: pinctrl cleanup for v4.9 Krzysztof Kozlowski
2016-09-19 15:48 ` Arnd Bergmann
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