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

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Date:	Tue, 16 Jul 2013 12:04:22 -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


A: No.
Q: Should I include quotations after my reply?

http://daringfireball.net/2007/07/on_top

On Tue, Jul 16, 2013 at 11:54:31AM -0700, Srinivas Pandruvada wrote:
> Hi,
> 
> I am assigned to do add a powercap class. There are several 
> technologies, which will allow to add a power budget to an individual
> device. For example, you can set a power budget to a individual
> physical cpu package, each core and uncore devices, GPUs, DRAM etc.

"classes" all reference a "device" in the system, I don't see that in
your tree below, where does that come in?  How do I, as someone who
created a device in the system know to create a your new powercap class
for it?

In other words, are you _sure_ you want a class here and not something
else (i.e. a bus?)

> +The Power Capping framework organizes power capping devices under a tree structure.
> +At the root level, each device is under some "controller", which is the enabler
> +of technology. For example this can be "RAPL".
> +Under each controllers, there are multiple power zones, which can be independently
> +monitored and controlled.
> +Each power zone can be organized as a tree with parent, children and siblings.
> +Each power zone defines attributes to enable power monitoring and constraints.

Ah, this sounds like you want to be a bus, as you have a controller, and
then devices attached to it.

> +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?

greg k-h
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