linux-kernel - Re: [PATCH 0/2] drivers: cpuidle: minor suspend-to-idle fixes

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Date:	Fri, 27 Feb 2015 10:00:00 +0000
From:	Lorenzo Pieralisi <lorenzo.pieralisi@....com>
To:	"Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:	Daniel Lezcano <daniel.lezcano@...aro.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	preeti@...ux.vnet.ibm.com
Subject: Re: [PATCH 0/2] drivers: cpuidle: minor suspend-to-idle fixes

[CC'ed Preeti]

On Thu, Feb 26, 2015 at 11:37:54PM +0000, Rafael J. Wysocki wrote:
> Me versions of the two $subject patches follow.

Thank you. I am testing them and I have run into the following issue.

Starting with:

3810631 ("PM / sleep: Re-implement suspend-to-idle handling")

the suspend-to-idle code path in the cpuidle_idle_call() bypasses
the CPUIDLE_FLAG_TIMER_STOP code path entirely. Now, on most of
the current ARM platforms, the deepest idle state loses the tick device
context, therefore this means that going to idle through
suspend-to-idle becomes a brute force way of nuking the tick,
unless I am missing something here.

I am experiencing hangs on resume from suspend-to-idle when the broadcast
timer is the broadast-hrtimer (ie there is no HW broadcast timer in the
platform) and the deepest idle states lose the tick device context (ie
they are CPUIDLE_FLAG_TIMER_STOP), I hope Preeti can help me test this on
Power, still chasing the issue.

I could not reproduce the issue with a HW broadcast timer device.

Platform has deepest idle states that allow CPUs shutdown where the
local tick device is gone on entry, I am trying to provide you with a
backtrace, I need time to debug.

The question I have: is it safe to bypass the CPUIDLE_FLAG_TIMER_STOP
and related broadcast mode entry/exit in the suspend-to-idle path ?

I do not think it is, but I am asking.

I can "force" tick freeze by initializing the enter_freeze pointer
in the idle states (that's the next thing I will test), but still, for
platforms where that's not possible my question above is still valid.

Thanks,
Lorenzo
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