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

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Message-ID: <564F6A92.7080006@arm.com>
Date:	Fri, 20 Nov 2015 18:46:42 +0000
From:	Marc Zyngier <marc.zyngier@....com>
To:	Grygorii Strashko <grygorii.strashko@...com>,
	santosh shilimkar <santosh.shilimkar@...cle.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 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.

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...
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