linux-kernel - RE: [PATCH 4/8] Thermal: Add Thermal

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Date:	Thu, 20 Dec 2012 16:58:32 +0000
From:	"R, Durgadoss" <durgadoss.r@...el.com>
To:	Greg KH <gregkh@...uxfoundation.org>
CC:	"Zhang, Rui" <rui.zhang@...el.com>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"hongbo.zhang@...aro.org" <hongbo.zhang@...aro.org>,
	"wni@...dia.com" <wni@...dia.com>
Subject: RE: [PATCH 4/8] Thermal: Add Thermal_trip sysfs node

> -----Original Message-----
> From: Greg KH [mailto:gregkh@...uxfoundation.org]
> Sent: Thursday, December 20, 2012 10:09 PM
> To: R, Durgadoss
> Cc: Zhang, Rui; linux-pm@...r.kernel.org; linux-kernel@...r.kernel.org;
> hongbo.zhang@...aro.org; wni@...dia.com
> Subject: Re: [PATCH 4/8] Thermal: Add Thermal_trip sysfs node
> 
> On Thu, Dec 20, 2012 at 04:25:32PM +0000, R, Durgadoss wrote:
> >
> > > -----Original Message-----
> > > From: Greg KH [mailto:gregkh@...uxfoundation.org]
> > > Sent: Thursday, December 20, 2012 9:42 PM
> > > To: R, Durgadoss
> > > Cc: Zhang, Rui; linux-pm@...r.kernel.org; linux-kernel@...r.kernel.org;
> > > hongbo.zhang@...aro.org; wni@...dia.com
> > > Subject: Re: [PATCH 4/8] Thermal: Add Thermal_trip sysfs node
> > >
> > > On Thu, Dec 20, 2012 at 07:52:03AM +0000, R, Durgadoss wrote:
> > > > > On Tue, Dec 18, 2012 at 02:59:33PM +0530, Durgadoss R wrote:
> > > > > > This patch adds a thermal_trip directory under
> > > > > > /sys/class/thermal/zoneX. This directory contains
> > > > > > the trip point values for sensors bound to this
> > > > > > zone.
> > > > >
> > > > > Eeek, you just broke userspace tools that now can no longer see
> these
> > > > > entries :(
> > > > >
> > > > > Why do you need to create a subdirectory?  As you found out, doing
> so
> > > > > isn't the easiest, right?  That is on purpose.
> > > >
> > > > Yes, I observed the complexity.
> > > >
> > > > >
> > > > > I really wouldn't recommend doing this at all, please stick within the
> > > > > 'struct device' framework here, don't create new kobjects and hang
> sysfs
> > > > > files off of them.
> > > >
> > > > But, we cannot put all _trip directly under ZoneX directory.
> > >
> > > Why not?  What is preventing this?
> > >
> > > > We can remove the thermal_trip directory, and put sensorY_trip under
> > > > /sys/class/thermal/zoneX/.  But this sensorY_trip needs to be a
> > > > directory which has four sysfs nodes named, active, passive, crit,
> > > > hot.
> > > >
> > > > Rui, What do you think about this ?
> > > >
> > > > The only other way I see, is directly put
> > > sensorY_trip_[active/passive/hot/crit]
> > > > which will create way too many nodes, under
> /sys/class/thermal/zoneX/.
> > >
> > > What is "too many"?  20000?  50000?  How many are we talking about
> here?
> >
> > Not in 1000's though..
> >
> > > What is the limiting factor that is preventing this from all going into
> > > one directory?
> >
> > We support a MAX of 12 sensors per zone today, which will lead to
> > 12 * 4, 48 nodes under this directory named
> > sensorY_trip_[active/passive/hot/crit], besides the other nodes.
> 
> That's fine, we can easily support that many files, have you tried this
> already?

Yes, in fact, this is sort of what was the old implementation..
although with different sysfs nodes.

> 
> The main point is, if you use a kobject like you are, userspace tools
> can't "see" these directories and files easily, if at all.  Try it out
> with libudev yourself to verify it, the attributes will not show up as
> owned to that device like you need them to be.

I haven't used libudev exactly, but I realized this sort of thing,
when I was trying to catch UEvents on this device path.

I will give libudev a try..

> 
> So put them all in one directory, we can handle 10's of thousands of
> files quite easily, so 48 is trivial :)

Okay, Will make it this way :-)
Now I can see the implementation getting much simpler !!

Thank you Greg,
Durga
P.S: I should thank you for this file(samples/kobject/kobject-example.c) also,
from where I got how to get this implementation done :-)
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