linux-kernel - RE: Kobject_uevent in cpufreq.c

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Date:	Mon, 13 May 2013 16:08:19 +0000
From:	"R, Durgadoss" <durgadoss.r@...el.com>
To:	"Greg KH (gregkh@...uxfoundation.org)" <gregkh@...uxfoundation.org>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Linux PM list (linux-pm@...r.kernel.org)" <linux-pm@...r.kernel.org>,
	"Wysocki, Rafael J" <rafael.j.wysocki@...el.com>
Subject: RE: Kobject_uevent in cpufreq.c

> -----Original Message-----
> From: linux-pm-owner@...r.kernel.org [mailto:linux-pm-
> owner@...r.kernel.org] On Behalf Of Greg KH
> (gregkh@...uxfoundation.org)
> Sent: Monday, May 13, 2013 5:28 PM
> To: R, Durgadoss
> Cc: linux-kernel@...r.kernel.org; Linux PM list (linux-pm@...r.kernel.org);
> Wysocki, Rafael J
> Subject: Re: Kobject_uevent in cpufreq.c
> 
> On Mon, May 13, 2013 at 11:31:57AM +0000, R, Durgadoss wrote:
> > Hi,
> >
> > I am observing an UEvent issue in cpufreq.c.
> > The cpufreq_add_dev() function is called whenever a core is 'onlined'.
> > we expect the kobject_uevent() method in cpufreq_add_dev() to
> > send an UEvent with KOBJ_ADD as the action parameter.
> >
> > But this call fails because of the 'filter function' inside kobject_uevent_env
> > inside lib/kobject_uevent.c. The ->filter points to 'dev_uevent_filter' in
> > drivers/base/core.c, where the check for 'device_ktype' fails.
> >
> > Error message:
> > kobject: 'cpufreq' (e5bbf290): kobject_uevent_env:
> > filter function caused the event to drop!
> >
> > As far as I can see, we need a kset, and associated filter function
> > inside cpufreq.c to get this working. Is this the right way to go ?
> > Any other easy/correct ways to get it working ? Please advise.
> 
> What exactly are you trying to do, and want the kernel to do?  You
> already get on/offline events for CPUs, why do you want them for cpufreq
> devices as well?

I want to update the permission of a cpufreq sysfs interface (scaling_*)
of a cpu (say cpu1) when the cpu resumes from suspend (s3).
I am trying to do this by listening to the uevent (sent by cpufreq.c,
when a cpu resumes) through udev.

For example,
chmod user:user /sys/devices/system/cpu1/cpufreq/scaling_max_freq

But I am not able to receive this event in udev, because kobject_uevent()
call fails due to the above-mentioned reason (i.e filter function)
I am trying to see how to make the kobject_uevent() call succeed,
so that I can change the permission as mentioned above.

The on/offline events come only when I manually do a
echo 0 > /sys/devices/system/cpu/cpu1/online
They don't come when the cpu resumes from suspend(s3)

[I checked this in code. Looks like during resume, the call flow
does not hit cpu.c, where this KOBJ_ONLINE is being sent]

Thanks,
Durga

> 
> thanks,
> 
> greg k-h
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