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 06:37:37 -0800
From:	Tony Lindgren <tony@...mide.com>
To:	Nishanth Menon <nm@...com>
Cc:	Paul Walmsley <paul@...an.com>, rnayak@...com, khilman@...aro.org,
	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

* 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.

Tony
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