[PATCH] arm: dts: exynos5: Remove multi core timer

[Doug Anderson]

Tomasz,

On Thu, May 15, 2014 at 2:14 PM, Tomasz Figa <tomasz.figa at 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.

-Doug