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

[Doug Anderson]

Kukjin,

On Fri, May 16, 2014 at 5:02 PM, Kukjin Kim <kgene.kim at samsung.com> wrote:
> 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.

I think we could wait a few days.  Note however, that Chirantan's
latest proposal keeps all existing functionality (can use both MCT and
arch timers).  It merely removes the unnecessary bit of the MCT init
code setting the timer.  No functionality is affected by that.

-Doug