linux-kernel - Re: [PATCH 2/2] ARM: omap: timers: reduce rating of gp

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Date:   Mon, 5 Dec 2016 09:42:24 +0530
From:   Keerthy <j-keerthy@...com>
To:     Tony Lindgren <tony@...mide.com>,
        Grygorii Strashko <grygorii.strashko@...com>
CC:     <t-kristo@...com>, <linux@...linux.org.uk>,
        <linux-omap@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, Dave Gerlach <d-gerlach@...com>
Subject: Re: [PATCH 2/2] ARM: omap: timers: reduce rating of gp_timer
 clocksource



On Saturday 03 December 2016 12:01 AM, Tony Lindgren wrote:
> * Grygorii Strashko <grygorii.strashko@...com> [161202 10:02]:
>>
>>
>> On 12/02/2016 10:47 AM, Tony Lindgren wrote:
>>> * Grygorii Strashko <grygorii.strashko@...com> [161129 08:43]:
>>>>
>>>>
>>>> On 11/24/2016 12:19 AM, Keerthy wrote:
>>>>> From: Grygorii Strashko <grygorii.strashko@...com>
>>>>>
>>>>> Now ARM Global timer (rating 300) will not be selected as clocksource,
>>>>> because it's initialized after OMAP GP Timer (rating 300) and
>>>>> Timekeeping core will not allow to replace clocksource with new one if
>>>>> both of them have the same rating.
>>>>>
>>>>> Reduce rating of OMAP GP Timer (300->290) when it's used as
>>>>> clocksource device - this will allow to select ARM Global timer (300)
>>>>> as clocksource when enabled.
>>>>>
>>>>> Signed-off-by: Grygorii Strashko <grygorii.strashko@...com>
>>>>> Signed-off-by: Dave Gerlach <d-gerlach@...com>
>>>>> Signed-off-by: Keerthy <j-keerthy@...com>
>>>>
>>>> Unfortunately, this patch has dependency [1] and can't be used alone as
>>>> it will cause ARM Global timer to be selected as clocksource
>>>> always on am437x and this will kill cpuidle, because ARM Global timer
>>>> is not in always_on domain.
>>>>
>>>> The intention of enabling ARM Global timer is only for non-pm aware use
>>>> cases for RT-kernel latency improvement - where deep cpuidle states are not
>>>> enabled.
>>>
>>> Yeah we need to fix up things to be able to change the clocksource
>>> in addition to clockevent. However, currently only cpuidle_coupled
>>> knows when the whole system is idle, so quite a bit of work is
>>> needed to do that in a sane way.
>>
>> Also sched_clock and timer_delay ;)
>
> Yeah sched_clock would need something to save and restore it..
> Not nice :)
>
>>> What about the first patch in this series?
>>>
>>
>> Fist one is ok. It was originally posted long time ago.
>
> OK so can you please resend that one more time with proper
> Fixes tag on it?

Tony,

I have posted a v2 with the proper Fixes tag.

- Keerthy
>
> Regards,
>
> Tony
>