Question about timers during system suspend

Question about timers during system suspend

[Raj Kumar]

Hi,
 
I have question regarding the timers during system suspend. If a software timer is
active in device driver, will this timer be stopped during system suspend?
 
If the timer is active, will it prevent the system from full suspend?
 
The another thing is during system suspend, how the user space code know about suspend?
 
One way is that device driver gets the suspend and it notifies the user space. 
 
But is there way that during system goes into full suspend, is any user space component that will
give notifications to applications that has registered for system suspend transition?
 
 
Regards
Raj 		 	   		  

Re: Question about timers during system suspend

[Rafael J. Wysocki]

On Tuesday, January 04, 2011, Raj Kumar wrote:
> 
> Hi,

Hi,

> I have question regarding the timers during system suspend. If a software timer is
> active in device driver, will this timer be stopped during system suspend?

What do you mean by "stopped"?  Do you mean canceled?

> If the timer is active, will it prevent the system from full suspend?

No, it won't.

> The another thing is during system suspend, how the user space code know about suspend?

It doesn't, unless it's notified by the user space process initiating suspend.

> One way is that device driver gets the suspend and it notifies the user space. 

That doesn't work, because user space is frozen when drivers' suspend routines
are being called.  It might work if the driver in question registered a power
management notifier and sent a notification to user space from there.

> But is there way that during system goes into full suspend, is any user space component that will
> give notifications to applications that has registered for system suspend transition?

That depends on the configuration of user space.  pm-utils can do that for one
example.

Thanks,
Rafael

Re: Question about timers during system suspend

[Raj Kumar]

 
Dear rafael,
 
Thanks for quick reply.
 
>> I have question regarding the timers during system suspend. If a software timer is
> > active in device driver, will this timer be stopped during system suspend?
>
> What do you mean by "stopped"? Do you mean canceled?
 
I mean cancel the software timer. But if the software timer is active as you already mentioned it will not prevent
system suspend. I mean to say if the driver has active software timer means software timer is not fired yet and device driver
will return from suspend callback without cancelation software timer and it times out after this
will not prevent system suspend to return error code.
 
right??
 
or is it mandatory to cancel the software timer during suspend callback to device driver?
 
 
Regards
raj
 



----------------------------------------
> From: rjw@sisk.pl
> To: rajkumar278@hotmail.com
> Subject: Re: [linux-pm] Question about timers during system suspend
> Date: Wed, 5 Jan 2011 00:05:42 +0100
> CC: linux-pm@lists.linux-foundation.org
>
> On Tuesday, January 04, 2011, Raj Kumar wrote:
> >
> > Hi,
>
> Hi,
>
> > I have question regarding the timers during system suspend. If a software timer is
> > active in device driver, will this timer be stopped during system suspend?
>
> What do you mean by "stopped"? Do you mean canceled?
>
> > If the timer is active, will it prevent the system from full suspend?
>
> No, it won't.
>
> > The another thing is during system suspend, how the user space code know about suspend?
>
> It doesn't, unless it's notified by the user space process initiating suspend.
>
> > One way is that device driver gets the suspend and it notifies the user space.
>
> That doesn't work, because user space is frozen when drivers' suspend routines
> are being called. It might work if the driver in question registered a power
> management notifier and sent a notification to user space from there.
>
> > But is there way that during system goes into full suspend, is any user space component that will
> > give notifications to applications that has registered for system suspend transition?
>
> That depends on the configuration of user space. pm-utils can do that for one
> example.
>
> Thanks,
> Rafael 		 	   		  

Re: Question about timers during system suspend

[Rafael J. Wysocki]

On Wednesday, January 05, 2011, Raj Kumar wrote:
> 
> Dear rafael,
>  
> Thanks for quick reply.
>  
> >> I have question regarding the timers during system suspend. If a software timer is
> > > active in device driver, will this timer be stopped during system suspend?
> >
> > What do you mean by "stopped"? Do you mean canceled?
>  
> I mean cancel the software timer. But if the software timer is active as you
> already mentioned it will not prevent system suspend. I mean to say if the
> driver has active software timer means software timer is not fired yet and
> device driver will return from suspend callback without cancelation software
> timer and it times out after this will not prevent system suspend to return
> error code.

I'm not really sure what you mean.  If the timer expires right after the
suspend routine has returned, then either the timer function will run
immediately (so you need to take that into consideration), if the timer
interrupt is still enabled at this point, or it will run during resume
(asynchronously with respect to the driver's resume routine).

> right??
>  
> or is it mandatory to cancel the software timer during suspend callback to device driver?

I guess it's better to cancel the timer directly from the suspend routine, but
it is not formally required to do so.

Thanks,
Rafael

 
> ----------------------------------------
> > From: rjw@sisk.pl
> > To: rajkumar278@hotmail.com
> > Subject: Re: [linux-pm] Question about timers during system suspend
> > Date: Wed, 5 Jan 2011 00:05:42 +0100
> > CC: linux-pm@lists.linux-foundation.org
> >
> > On Tuesday, January 04, 2011, Raj Kumar wrote:
> > >
> > > Hi,
> >
> > Hi,
> >
> > > I have question regarding the timers during system suspend. If a software timer is
> > > active in device driver, will this timer be stopped during system suspend?
> >
> > What do you mean by "stopped"? Do you mean canceled?
> >
> > > If the timer is active, will it prevent the system from full suspend?
> >
> > No, it won't.
> >
> > > The another thing is during system suspend, how the user space code know about suspend?
> >
> > It doesn't, unless it's notified by the user space process initiating suspend.
> >
> > > One way is that device driver gets the suspend and it notifies the user space.
> >
> > That doesn't work, because user space is frozen when drivers' suspend routines
> > are being called. It might work if the driver in question registered a power
> > management notifier and sent a notification to user space from there.
> >
> > > But is there way that during system goes into full suspend, is any user space component that will
> > > give notifications to applications that has registered for system suspend transition?
> >
> > That depends on the configuration of user space. pm-utils can do that for one
> > example.
> >
> > Thanks,
> > Rafael 		 	   		  
> 

Question about hibernation

[Raj Kumar]

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Hi,

I have following question regarding the hibernation. If a device driver uses dedicated memory (dedicated memory in linux which is not OS addressable e.g. device driver is using some pages from dedicated memory), When the system hibernates, will this be responsibility of device driver to save this area 
or 
OS hibernation procedure save this area of ram (dedicated memory area) into swap image?

Thanks
Raj  
 		 	   		  

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Re: Question about hibernation

[Oliver Neukum]

Am Freitag, 18. März 2011, 14:45:24 schrieb Raj Kumar:
> 
> Hi,
> 
> I have following question regarding the hibernation. If a device driver uses dedicated memory (dedicated memory in linux which is not OS addressable e.g. device driver is using some pages from dedicated memory), When the system hibernates, will this be responsibility of device driver to save this area 
> or 
> OS hibernation procedure save this area of ram (dedicated memory area) into swap image?

If you got it from get_free_pages (at the end of a long call chain) the
kernel saves it. If not, it is your problem.

	HTH
		Oliver

Re: Question about hibernation

[Raj Kumar]

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Hi,
 
Thanks for reply. What if memory is allocated using dma_alloc_coherent where the physical address is from dedicated area of RAM(which is not addressable by OS)? I also believe that all the buffers and state variables are taken care by OS kernel. Right?
 
Thanks
Raj
 

 
> From: oneukum@suse.de
> To: linux-pm@lists.linux-foundation.org
> Subject: Re: [linux-pm] Question about hibernation
> Date: Fri, 18 Mar 2011 15:09:02 +0100
> CC: rajkumar278@hotmail.com
> 
> Am Freitag, 18. März 2011, 14:45:24 schrieb Raj Kumar:
> > 
> > Hi,
> > 
> > I have following question regarding the hibernation. If a device driver uses dedicated memory (dedicated memory in linux which is not OS addressable e.g. device driver is using some pages from dedicated memory), When the system hibernates, will this be responsibility of device driver to save this area 
> > or 
> > OS hibernation procedure save this area of ram (dedicated memory area) into swap image?
> 
> If you got it from get_free_pages (at the end of a long call chain) the
> kernel saves it. If not, it is your problem.
> 
> HTH
> Oliver
 		 	   		  

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