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

From: [email-masked] (Kukjin Kim)
Date: Sat, 17 May 2014 09:02:46 +0900

On 05/17/14 07:56, Chirantan Ekbote wrote:
>>>> Anyway, I'm by no means opposed to switching to arch timers. They
>>>> provide a well designed, generic interface and drivers shared by
>>>> multiple platforms, which means more code sharing and possibly more eyes
>>>> looking at the code, which is always good. However if they don't support
>>>> low power states correctly, we can't just remove MCT.
>>>
>>> I think low power states aren't in mainline (right?).
>>>
>>> One solution that might work could be to leave the device tree entry
>>> alone but change the MCT init code to simply act as a no-op if it sees
>>> an arch timer is in the device tree and enabled.  Then when/if someone
>>> got the low power states enabled we could just change source code
>>> rather than dts files.
>>>
>
> Doug and I were talking about this and we think we may have a way to
> have the mct and arch timers co-exist.  The main issue is that the mct
> (and therefore arch timer) gets cleared once during boot and every
> time we do a suspend / resume.  This happens in
> exynos4_mct_frc_start() but it's not immediately clear to us why the
> counter needs to be reset at all.  If we remove the lines that clear
> the counter then there is no longer an issue with having both the mct
> and the arch timers on at the same time.
>
> Alternately, if there is some code that depends on the mct being reset
> we could store an offset instead of clearing the counter and then
> subtract that offset every time something reads it.  Doug has a patch
> that does this at
> https://chromium-review.googlesource.com/#/c/200298/.  Effectively the
> visible behavior will not change.  Would either of these options work?
>
Hi all,

Even though I've heard something about the behavior of mct and arch 
timer...but I couldn't finish the talk to h/w guys yet. I need to talk 
again in next week then I could provide some useful information. Sorry 
for late and can you please wait a minute before deciding whatever.

Thanks,
Kukjin