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

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Date:	Fri, 22 Nov 2013 14:01:20 -0500
From:	Santosh Shilimkar <santosh.shilimkar@...com>
To:	Kevin Hilman <khilman@...aro.org>
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

On Friday 22 November 2013 01:43 PM, Kevin Hilman wrote:
> 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().
> 
You are right. I realized that after reading the code.

> 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.
> 
Agree.

> I'll need to think about this a little more before having any idea what
> to do here.
> 
Thanks Kevin for looking into it.

Regards,
Santosh

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