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

[Kevin Hilman <khilman@linaro.org>]

Nishanth Menon <nm@ti.com> writes:

> On 16:38-20131107, Kevin Hilman wrote:
> [...]
>> That's debatable I guess.  The ideal world is that runtime PM hides all
>> of this, but I'm not sure it's achievable in all cases.
>> 
> Agreed. some drivers like edma need to save and restore context around
> suspend.
> [...]
>
>> No, that sysfs knob is for disabling runtime PM.  We still want the
>> device to hit low-power state in system suspend.  Solving that problem
>> is half the reason we have this omap_device noirq mess in the first
>> place.
>> 
>> You need to test this by disabling runtime PM from userspace and ensure
>> that the low power state is still hit during suspend.
>> 
> Done and it still does work, makes sense since it just ensures that
> runtime PM's dev->power.runtime_status is set to RPM_SUSPENDED instead
> of RPM_ACTIVE for devices that depend on autosuspend.
>
> Logs (based on vendor kernel which has relevant out of tree patches to
> enable suspend resume - still in the works):
> AM335x-BBB: http://pastie.org/8472182
> OMAP5-uEVM: http://pastie.org/8472183
>
>> >>
>> >>> +				/* NOTE: *might* indicate driver race */
>> >>
>> >> Yes, a driver race which should then be fixed in the driver.
>> >
>> > true if this is a non-autosuspend device, in auto suspend devices,
>> > this could be a regular phenomenon if timeout is pretty large.. but
>> > atleast that should allow debug.
>> 
>> Agreed.  I wasn't thinking about the autosuspend case.  Thanks for
>> clarifying.
>> 
>> >>
>> >>> +				dev_dbg(dev, "%s: Force suspending\n",
>> >>> +					__func__);
>> >>> +				pm_runtime_set_suspended(dev);
>> >>> +				od->flags |= OMAP_DEVICE_SUSPEND_FORCED;
>> >>
>> >> Not sure why you need an additonal flag.  Why not just always do this
>> >> and use the existin OMAP_DEVICE_SUSPENDED flag.
>> >
>> > restore of runtime data structure state is only needed for specific
>> > devices - not all..
>> 
>> The question is why do you a flag in addition to OMAP_DEVICE_SUSPEND.
>> Whenever that flag is set, omap_device has gone behind your back, and
>> the runtime PM status should be kept in sync.
>
> Yes, you are right, originally, I had intended this to indicate devices
> that needed to be runtime_status updated, but then, now I realize that
> it is true for all devices that have OMAP_DEVICE_SUSPEND set. It can be
> applied without an additional flag. Do see if the updated patch is more
> sensible:

Yes, the updated version looks much more sensible.  Please repost in its
own thread so it gets a better chance at broader review, and feel free
to add

Acked-by: Kevin Hilman <khilman@linaro.org>

Kevin

> -- >8 --
> From 96b5a7b89fef4ba55bca48bae83e5536d697c6c4 Mon Sep 17 00:00:00 2001
> From: Nishanth Menon <nm@ti.com>
> Date: Thu, 24 Oct 2013 09:12:42 -0500
> Subject: [PATCH V2] ARM: OMAP2+: omap_device: maintain sane runtime pm status
>  around suspend/resume
>
> 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.
>
> Reported-by: J Keerthy <j-keerthy@ti.com>
> Signed-off-by: Nishanth Menon <nm@ti.com>
> Acked-by: Rajendra Nayak <rnayak@ti.com>
> ---
>  arch/arm/mach-omap2/omap_device.c |    5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/arch/arm/mach-omap2/omap_device.c b/arch/arm/mach-omap2/omap_device.c
> index b69dd9a..f97b34b 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 +635,10 @@ 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);
> +		pm_runtime_set_active(dev);
>  		pm_generic_runtime_resume(dev);
>  	}
>  
> -- 
> 1.7.9.5