linux-kernel - Re: [PATCH] PM / Clocks: fix pm_clk_resume/suspend if CONFIG_PM

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Date:	Fri, 22 Nov 2013 10:43:49 -0800
From:	Kevin Hilman <khilman@...aro.org>
To:	Santosh Shilimkar <santosh.shilimkar@...com>
Cc:	Grygorii Strashko <grygorii.strashko@...com>,
	Stephen Boyd <sboyd@...eaurora.org>,
	Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	<linux-kernel@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>, <linux-pm@...r.kernel.org>,
	Mike Turquette <mturquette@...aro.org>,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>
Subject: Re: [PATCH] PM / Clocks: fix pm_clk_resume/suspend if CONFIG_PM_RUNTIME is set

Santosh Shilimkar <santosh.shilimkar@...com> writes:

[...]

>>> It looks like even if you just remove the locks here, the PM core is
>>> free to call this function with irqs disabled if pm_runtime_irq_safe()
>>> has been called on the device. Perhaps runtime PM can only do the
>>> clk_enable()/clk_disable() part and the clk_unprepare()/clk_prepare()
>>> calls should happen in the system suspend callbacks?
>> 
>> Even don't know what to say :( On Keystone clk_unprepare()/clk_prepare() are NOPs.
>> But clk_prepare() has to be called at least once before clk_enable() :((
>> So, solution with suspend/resume will not fix current problem :( unfortunately.
>> 
>> FYI, Now pm_clk_suspend/pm_clk_resume are called from arch/arm/mach-keystone/pm_domain.c
>> (also similar solution is used by Davinci, but issue has not been detected because
>> PM runtime hasn't been used by Davinci IP drivers before)
>> 
> One way to deal with this is to have clk_unprepare()/clk_prepare()
> called from dev_pm_domain ops before calling pm_clk_[suspend/resume]() if we
> can't have that as part of runtime code.

That doesn't solve the irq_safe problem that Stephen pointed out without
being very careful.  Basically, if you have _any_ potentially sleeping
calls in this path, you can never allow devices to use
pm_runtime_irq_safe().

Also, I don't like having the clk_enable in the PM core but the
clk_prepare in the platform-specific pm_domain.  That seems prone for
platforms to get wrong.

I'll need to think about this a little more before having any idea what
to do here.

Kevin






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