linux-kernel - Re: [PATCH V3] ARM: OMAP2+: omap_device: maintain sane runtime pm status around suspend/resume

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Date:	Fri, 15 Nov 2013 14:03:55 -0800
From:	Kevin Hilman <khilman@...aro.org>
To:	Tony Lindgren <tony@...mide.com>
Cc:	Nishanth Menon <nm@...com>, Paul Walmsley <paul@...an.com>,
	rnayak@...com, balbi@...com, linux-omap@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH V3] ARM: OMAP2+: omap_device: maintain sane runtime pm status around suspend/resume

Tony Lindgren <tony@...mide.com> writes:

> * Nishanth Menon <nm@...com> [131115 05:30]:
>> On 11/15/2013 02:07 AM, Paul Walmsley wrote:
>> > On Thu, 14 Nov 2013, Nishanth Menon wrote:
>> > 
>> >> OMAP device hooks around suspend|resume_noirq ensures that hwmod
>> >> devices are forced to idle using omap_device_idle/enable as part of
>> >> the last stage of suspend activity.
>> >>
>> >> For a device such as i2c who uses autosuspend, it is possible to enter
>> >> the suspend path with dev->power.runtime_status = RPM_ACTIVE.
>> >>
>> >> As part of the suspend flow, the generic runtime logic would increment
>> >> it's dev->power.disable_depth to 1. This should prevent further
>> >> pm_runtime_get_sync from succeeding once the runtime_status has been
>> >> set to RPM_SUSPENDED.
>> >>
>> >> Now, as part of the suspend_noirq handler in omap_device, we force the
>> >> following: if the device status is !suspended, we force the device
>> >> to idle using omap_device_idle (clocks are cut etc..). This ensures
>> >> that from a hardware perspective, the device is "suspended". However,
>> >> runtime_status is left to be active.
>> >>
>> >> *if* an operation is attempted after this point to
>> >> pm_runtime_get_sync, runtime framework depends on runtime_status to
>> >> indicate accurately the device status, and since it sees it to be
>> >> ACTIVE, it assumes the module is functional and returns a non-error
>> >> value. As a result the user will see pm_runtime_get succeed, however a
>> >> register access will crash due to the lack of clocks.
>> >>
>> >> To prevent this from happening, we should ensure that runtime_status
>> >> exactly indicates the device status. As a result of this change
>> >> any further calls to pm_runtime_get* would return -EACCES (since
>> >> disable_depth is 1). On resume, we restore the clocks and runtime
>> >> status exactly as we suspended with. These operations are not expected
>> >> to fail as we update the states after the core runtime framework has
>> >> suspended itself and restore before the core runtime framework has
>> >> resumed.
>> >>
>> >> Reported-by: J Keerthy <j-keerthy@...com>
>> >> Signed-off-by: Nishanth Menon <nm@...com>
>> >> Acked-by: Rajendra Nayak <rnayak@...com>
>> >> Acked-by: Kevin Hilman <khilman@...aro.org>
>> > 
>> > Looks reasonable to me.  Looks like this should be considered for -stable 
>> > - Nishanth, what do you think?
>> 
>> Every product kernel since 3.4 needed to be hacked (we have hacked in
>> different ways so far) to work around this (since we never spend time
>> digging deeper :( ), So, I do agree with your view that a -stable tag
>> will be most beneficial.
>> 
>> > 
>> > Tony or Kevin, do you want to take this one, or want me to?
>
> I can take it unless you have other fixes pending right now.

This version looks good to me.

Reviewed-by: Kevin Hilman <khilman@...aro.org>

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