From: kgene.kim@samsung•com (Kukjin Kim)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH] arm: dts: exynos5: Remove multi core timer
Date: Fri, 16 May 2014 06:44:02 +0900 [thread overview]
Message-ID: <53753522.30107@samsung.com> (raw)
In-Reply-To: <CAD=FV=WKOtZaUyzTWNqR=vi_L=U-Q1dct2U_oCYi3ZJv6401Hg@mail.gmail.com>
On 05/16/14 06:33, Doug Anderson wrote:
> Tomasz,
>
> On Thu, May 15, 2014 at 2:14 PM, Tomasz Figa<tomasz.figa@gmail•com> wrote:
>> Hi Chirantan,
>>
>> On 15.05.2014 23:07, Chirantan Ekbote wrote:
>>> The multi core timer and the ARM architected timer are two different
>>> interfaces to the same underlying hardware timer. This causes some
>>> strange timing issues when they are both enabled at the same time so
>>> remove the mct from the device tree and keep only the architected
>>> timer.
>>
>> Huh? I've always thought MCT is a completely separate hardware block
>> outside of ARM cores, while architected timers are embedded inside the
>> CPU block in which the ARM cores reside. Could you elaborate on this?
>
> Yup. Our thoughts exactly.
>
> ...but it appears not to be the case. Chirantan demonstrated this in
> U-Boot just to prove that it's not some strange kernel interaction in
> <https://chromium-review.googlesource.com/200035>. I took his patch
> and tweaked it a little more myself in
> <https://chromium-review.googlesource.com/200098>.
>
> Specifically:
> * If you stop the MCT, the arch timer stops
> * If you reset the MCT, the arch timer resets
> * If you start the MCT again, the arch timer starts again
> * If you read the MCT and the arch timer, they give the same value.
>
>
> This is apparently the answer to my question at
> <http://www.spinics.net/lists/linux-samsung-soc/msg29085.html>.
> Specifically Chirantan found that the big jump in time happened when
> MCT reset to 0. That made the arch timer code think that there was a
> wraparound and jump forward in time a lot.
>
>
> Please confirm if you have a system that has MCT and arch timer in front of you.
>
Hi all,
I need to talk to hardware guy to clarify the issue then I'll let you know.
Thanks,
Kukjin
next prev parent reply other threads:[~2014-05-15 21:44 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-05-15 21:07 [PATCH] arm: dts: exynos5: Remove multi core timer Chirantan Ekbote
2014-05-15 21:14 ` Tomasz Figa
2014-05-15 21:33 ` Doug Anderson
2014-05-15 21:40 ` Tomasz Figa
2014-05-15 21:54 ` Doug Anderson
2014-05-15 22:13 ` Tomasz Figa
2014-05-15 22:44 ` Doug Anderson
2014-05-15 23:03 ` Chirantan Ekbote
2014-05-15 23:18 ` David Riley
2014-05-15 23:25 ` Tomasz Figa
2014-05-15 23:39 ` Olof Johansson
2014-05-15 23:45 ` Doug Anderson
2014-05-15 23:46 ` Tomasz Figa
2014-05-15 23:43 ` Doug Anderson
2014-05-16 0:31 ` Sonny Rao
2014-05-16 22:56 ` Chirantan Ekbote
2014-05-17 0:02 ` Kukjin Kim
2014-05-19 15:12 ` Doug Anderson
2014-05-21 13:24 ` Kukjin Kim
2014-05-21 15:30 ` Olof Johansson
2014-05-21 16:20 ` Tomasz Figa
2014-05-21 18:34 ` Chirantan Ekbote
2014-05-28 17:38 ` Doug Anderson
2014-06-02 23:22 ` Doug Anderson
2014-05-21 12:47 ` Kukjin Kim
2014-05-21 18:34 ` Chirantan Ekbote
2014-05-28 17:23 ` Doug Anderson
2014-06-03 18:41 ` Chirantan Ekbote
2014-06-04 1:45 ` Kukjin Kim
2014-05-28 17:37 ` Doug Anderson
2014-05-29 20:42 ` Vincent Guittot
2014-05-29 21:41 ` Doug Anderson
2014-05-15 21:44 ` Kukjin Kim [this message]
2014-05-15 21:44 ` Tomasz Figa
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