linux-kernel - Re: driver model, duplicate names question

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Date:	Tue, 16 Jul 2013 12:32:35 -0700
From:	Greg KH <gregkh@...uxfoundation.org>
To:	Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
Cc:	Linux Kernel <linux-kernel@...r.kernel.org>,
	"Brown, Len" <len.brown@...el.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>
Subject: Re: driver model, duplicate names question

On Tue, Jul 16, 2013 at 12:33:03PM -0700, Srinivas Pandruvada wrote:
> >> +Example Sys-FS Interface
> >> +
> >> +/sys/class/power_cap/intel-rapl
> >> +├── package-0
> >> +│   ├── constraint-0
> >> +│   │   ├── name
> >> +│   │   ├── power_limit_uw
> >> +│   │   └── time_window_us
> >> +│   ├── constraint-1
> >> +│   │   ├── name
> >> +│   │   ├── power_limit_uw
> >> +│   │   └── time_window_us
> >> +│   ├── core
> >> +│   │   ├── constraint-0
> >> +│   │   │   ├── name
> >> +│   │   │   ├── power_limit_uw
> >> +│   │   │   └── time_window_us
> >> +│   │   ├── energy_uj
> >> +│   │   └── max_energy_range_uj
> >> +│   ├── dram
> >> +│   │   ├── constraint-0
> >> +│   │   │   ├── name
> >> +│   │   │   ├── power_limit_uw
> >> +│   │   │   └── time_window_us
> >> +│   │   ├── energy_uj
> >> +│   │   └── max_energy_range_uj
> >> +│   ├── energy_uj
> >> +│   ├── max_energy_range_uj
> >> +│   └── max_power_range_uw
> >> +├── package-1
> >> +│   ├── constraint-0
> >> +│   │   ├── name
> >> +│   │   ├── power_limit_uw
> >> +│   │   └── time_window_us
> >> +│   ├── constraint-1
> >> +│   │   ├── name
> >> +│   │   ├── power_limit_uw
> >> +│   │   └── time_window_us
> >> +│   ├── core
> >> +│   │   ├── constraint-0
> >> +│   │   │   ├── name
> >> +│   │   │   ├── power_limit_uw
> >> +│   │   │   └── time_window_us
> >> +│   │   ├── energy_uj
> >> +│   │   └── max_energy_range_uj
> >> +│   ├── dram
> >> +│   │   ├── constraint-0
> >> +│   │   │   ├── name
> >> +│   │   │   ├── power_limit_uw
> >> +│   │   │   └── time_window_us
> >> +│   │   ├── energy_uj
> >> +│   │   └── max_energy_range_uj
> >> +│   ├── energy_uj
> >> +│   ├── max_energy_range_uj
> >> +│   └── max_power_range_uw
> >> +├── power
> >> +│   ├── async
> >> +│   ├── autosuspend_delay_ms
> >> +│   ├── control
> >> +│   ├── runtime_active_kids
> >> +│   ├── runtime_active_time
> >> +│   ├── runtime_enabled
> >> +│   ├── runtime_status
> >> +│   ├── runtime_suspended_time
> >> +│   └── runtime_usage
> >> +├── subsystem -> ../../../../class/power_cap
> >> +└── uevent
> > Ick.  Rewrite this to use a bus and you should be fine, right?  Don't
> > use a class, a class is only to be used if you have a device that is a
> > specific "type of thing".  Like a tty device, it is a class, as lots of
> > different "real" devices can have tty ports on them (usb, pci, pcmcia,
> > platform, etc.)
> >
> > Rethink this using a bus and see if that solves your issues.  You get a
> > hierarchy with that.  And you can have different "types" of devices on
> > your bus, making it easy to tell the difference between a "package" and
> > a "constraint".
> >
> > Does that help?
> I will experiment your suggestion. I see this class analogous to 
> "/sys/class/thermal",
> , where the thermal class provides a set of consistent interface for all 
> thermal devices.

But thermal devices are not "real" at all.  There are just a number of
"cooling devices" on a virtual bus and not attached to any type of a
real device at all.

There's also no hierarchy that I can see with the thermal class, but you
want to have this, so you will have to do something different because
classes do not have hierarchies.

So try using a device and a bus and see if that helps out.  If not,
please let me know.

thanks,

greg k-h
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