From: Grygorii Strashko <grygorii.strashko@ti.com>
To: John Stultz <john.stultz@linaro.org>
Cc: santosh shilimkar <santosh.shilimkar@oracle.com>,
Russell King - ARM Linux <linux@arm.linux.org.uk>,
Daniel Lezcano <daniel.lezcano@linaro.org>,
Thomas Gleixner <tglx@linutronix.de>,
Srinivas Kandagatla <srinivas.kandagatla@gmail.com>,
Maxime Coquelin <maxime.coquelin@st.com>,
lkml <linux-kernel@vger.kernel.org>,
"linux-arm-kernel@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>, <kernel@stlinux.com>,
"linux-omap@vger.kernel.org" <linux-omap@vger.kernel.org>,
Arnd Bergmann <arnd@arndb.de>, Felipe Balbi <balbi@ti.com>,
Tony Lindgren <tony@atomide.com>,
Santosh Shilimkar <ssantosh@kernel.org>,
Marc Zyngier <marc.zyngier@arm.com>
Subject: Re: [PATCH v2] clocksource: arm_global_timer: fix suspend resume
Date: Fri, 20 Nov 2015 21:28:07 +0200 [thread overview]
Message-ID: <564F7447.8000504@ti.com> (raw)
In-Reply-To: <CALAqxLVLQLaAq7fPwJnyOWP_dXV39Dh+QreecxSVY35wi=N0Og@mail.gmail.com>
On 11/20/2015 09:09 PM, John Stultz wrote:
> On Fri, Nov 20, 2015 at 10:35 AM, Grygorii Strashko
> <grygorii.strashko@ti.com> 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@arm.com>
>> Date: Tue Apr 8 10:04:32 2014 +0100
>>
>> clocksource: arch_arm_timer: Fix age-old arch timer C3STOP detection issue
>>
>>
>> - and followed timekeeping.txt:
>> "Typically the clock source is a monotonic, atomic counter which will provide
>> n bits which count from 0 to 2^(n-1) and then wraps around to 0 and start over.
>> It will ideally NEVER stop ticking as long as the system is running. It
>> may stop during system suspend."
>> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>>
>> And that exactly my use-case: I'd like to use ARM GT as clocksource
>> and with CPUIdle = n. But System suspend has to be allowed.
>>
>>
>>>
>>> Also if the clock-soucre can't tick in the low power states
>>> then that device shouldn't be used as a clock-source.
>>
>> Agree. clocksource can't (except with suspend). Have I missed something?
>
> I think the point Stantosh is making is that if the clocksource stops
> in suspend (which is allowed) you should not be setting
> CLOCK_SOURCE_SUSPEND_NONSTOP (which promises the clocksource doesn't
> stop in suspend, so it can be used for suspend timing as well).
>
Ok. Thanks. I got it now. Adding CLOCK_SOURCE_SUSPEND_NONSTOP is mistake.
> The contradictory part in your patch is that you're also setting the
> clockevent logic as CLOCK_EVT_FEAT_C3STOP, which flags that the
> clockevent hardware might stop in low-power idle states (ie: not
> suspend, but while the system is running). Usually hardware that
> halts in low-power mode (like the apic on some x86 machines) is not
> also used for timekeeping (instead we use the hpet/acpi there).
Sry, I've set CLOCK_EVT_FEAT_C3STOP if "always-on" = *false*
^ this, I thought, might be valid because it will stop in low-power idle states
and "always-on" was expected to indicate case when CPUIdle = n (no CPU PM),
same way as Lorenzo did.
Would it be correct to just set it always?
and CLOCK_SOURCE_SUSPEND_NONSTOP if "always-on" = *true*
^ this part is mistake
>
> So its unlikely that the hardware both stays running through suspend,
> but also might halt in idle. That would be "unique".
>
Thanks a lot.
--
regards,
-grygorii
next prev parent reply other threads:[~2015-11-20 19:29 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-11-20 13:57 [PATCH v2] clocksource: arm_global_timer: fix suspend resume Grygorii Strashko
2015-11-20 17:23 ` santosh shilimkar
2015-11-20 18:35 ` Grygorii Strashko
2015-11-20 18:46 ` Marc Zyngier
2015-11-20 18:52 ` santosh shilimkar
2015-11-20 19:12 ` Grygorii Strashko
2015-11-20 19:11 ` John Stultz
2015-11-20 19:09 ` John Stultz
2015-11-20 19:25 ` Thomas Gleixner
2015-11-20 19:28 ` Grygorii Strashko [this message]
2015-11-20 19:32 ` John Stultz
2015-11-20 20:42 ` Grygorii Strashko
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