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 08:07:34 +0000 (UTC)
From:	Paul Walmsley <paul@...an.com>
To:	Nishanth Menon <nm@...com>
cc:	Tony Lindgren <tony@...mide.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

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?

Tony or Kevin, do you want to take this one, or want me to?


- Paul
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