linux-kernel - Re: [PATCH v2] clocksource: arm_global

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Date:	Fri, 20 Nov 2015 10:52:00 -0800
From:	santosh shilimkar <santosh.shilimkar@...cle.com>
To:	Marc Zyngier <marc.zyngier@....com>,
	Grygorii Strashko <grygorii.strashko@...com>,
	linux@....linux.org.uk, Daniel Lezcano <daniel.lezcano@...aro.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Srinivas Kandagatla <srinivas.kandagatla@...il.com>,
	Maxime Coquelin <maxime.coquelin@...com>
Cc:	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	kernel@...inux.com, linux-omap@...r.kernel.org,
	Arnd Bergmann <arnd@...db.de>,
	John Stultz <john.stultz@...aro.org>,
	Felipe Balbi <balbi@...com>, Tony Lindgren <tony@...mide.com>,
	Santosh Shilimkar <ssantosh@...nel.org>
Subject: Re: [PATCH v2] clocksource: arm_global_timer: fix suspend resume

On 11/20/2015 10:46 AM, Marc Zyngier wrote:
> On 20/11/15 18:35, Grygorii Strashko wrote:
>> Hi Santosh,
>>
>> On 11/20/2015 07:23 PM, santosh shilimkar wrote:
>>> + Thomas, Marc
>>>
>>> On 11/20/2015 5:57 AM, Grygorii Strashko wrote:
>>>> Now the System stall is observed on TI AM437x based board
>>>> (am437x-gp-evm) during resuming from System suspend when ARM Global
>>>> timer is selected as clocksource device - SysRq are working, but
>>>> nothing else. The reason of stall is that ARM Global timer loses its
>>>> contexts.
>>>>
>>>> The reason of stall is that ARM Global timer loses its contexts during
>>>> System suspend:
>>>>      GT_CONTROL.TIMER_ENABLE = 0 (unbanked)
>>>>      GT_COUNTERx = 0
>>>>
>>>> Hence, update ARM Global timer driver to reflect above behaviour
>>>> - re-enable ARM Global timer on resume GT_CONTROL.TIMER_ENABLE = 1
>>>> - ensure clocksource and clockevent devices have coresponding flags
>>>>     (CLOCK_SOURCE_SUSPEND_NONSTOP and CLOCK_EVT_FEAT_C3STOP) set
>>>>     depending on presence of "always-on" DT property.
>>>>
>>> Something which loses context in low power states can't be
>>> called "always-on"
>>
>> Sry, it's kinda new area for me and I could make mistakes.
>>
>> While working on this patch I've:
>>   - re-used implementation from ARM arch timer
>> commit 82a5619410d4c4df65c04272db198eca5a867c18
>> Author: Lorenzo Pieralisi <lorenzo.pieralisi@....com>
>> Date:   Tue Apr 8 10:04:32 2014 +0100
>>
>>      clocksource: arch_arm_timer: Fix age-old arch timer C3STOP detection issue
>
> [...]
>
> This patch has a very specific purpose: instructing the core code that
> this timer will never stop ticking, ever. It is really targeted at
> virtual machines, whose timer is backed by the host timer, even when the
> VM is not running.
>
> Using it on actual hardware is may not be the best idea, specially in
> the presence of PM.
>
Exactly. Thanks for clarifying the commit Marc.

Regards,
Santosh
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