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

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Date:	Thu, 14 Nov 2013 12:55:58 -0600
From:	Felipe Balbi <balbi@...com>
To:	Nishanth Menon <nm@...com>
CC:	Tony Lindgren <tony@...mide.com>, <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

Hi,

On Thu, Nov 14, 2013 at 11:05:16AM -0600, 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>
> ---
> Changes in V3:
> 	- Added WARN in case of unexpected failure of runtime pm status restore
> v2: https://patchwork.kernel.org/patch/3176501/
> v1: https://patchwork.kernel.org/patch/3154501/
> 
> patch baseline: V3.12 tag (also applies on linux-next next-20131107 tag)
> 
>  arch/arm/mach-omap2/omap_device.c |   13 +++++++++++--
>  1 file changed, 11 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/arm/mach-omap2/omap_device.c b/arch/arm/mach-omap2/omap_device.c
> index b69dd9a..53f0735 100644
> --- a/arch/arm/mach-omap2/omap_device.c
> +++ b/arch/arm/mach-omap2/omap_device.c
> @@ -621,6 +621,7 @@ static int _od_suspend_noirq(struct device *dev)
>  
>  	if (!ret && !pm_runtime_status_suspended(dev)) {
>  		if (pm_generic_runtime_suspend(dev) == 0) {
> +			pm_runtime_set_suspended(dev);
>  			omap_device_idle(pdev);
>  			od->flags |= OMAP_DEVICE_SUSPENDED;
>  		}
> @@ -634,10 +635,18 @@ static int _od_resume_noirq(struct device *dev)
>  	struct platform_device *pdev = to_platform_device(dev);
>  	struct omap_device *od = to_omap_device(pdev);
>  
> -	if ((od->flags & OMAP_DEVICE_SUSPENDED) &&
> -	    !pm_runtime_status_suspended(dev)) {
> +	if (od->flags & OMAP_DEVICE_SUSPENDED) {
>  		od->flags &= ~OMAP_DEVICE_SUSPENDED;
>  		omap_device_enable(pdev);
> +		/*
> +		 * XXX: we run before core runtime pm has resumed itself. At
> +		 * this point in time, we just restore the runtime pm state and
> +		 * considering symmetric operations in resume, we donot expect
> +		 * to fail. If we failed, something changed in core runtime_pm
> +		 * framework OR some device driver messed things up, hence, WARN
> +		 */
> +		WARN(pm_runtime_set_active(dev),
> +		     "Could not set %s runtime state active\n", dev_name(dev));

if you want to print the device name, how about dev_WARN() ?

no strong feelings though:

Reviewed-by: Felipe Balbi <balbi@...com>

-- 
balbi

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