-----Original Message-----
From:=20
devicetree-discuss-bounces+leoli=3Dfreescale.com@ozlabs.org=20
[mailto:devicetree-discuss-bounces+leoli=3Dfreescale.com@ozlabs.
org] On Behalf Of David Gibson
Sent: Tuesday, January 06, 2009 9:43 AM
To: Wood Scott-B07421
Cc: linuxppc-dev@ozlabs.org; Li Yang-R58472;=20
devicetree-discuss@ozlabs.org
Subject: Re: The usage of compatible 'simple-bus'
=20
On Mon, Jan 05, 2009 at 01:20:53PM -0600, Scott Wood wrote:

quoted

On Mon, Jan 05, 2009 at 06:27:39PM +0800, Li Yang wrote:

quoted

I got an assumption from the existing device trees that having=20
'simple-bus' in the compatible property of a node means that all=20
child nodes should be added as of_platform_device in platform=20
initialization phase.  No matter it represents a bus in=20

common sense=20

quoted

quoted

or not.  Is this truly the case?

=20
Yes, simple-bus indicates that the children can be driven=20

standalone=20

quoted

from any knowledge of the parent bus.

=20
Erm, well, sort of.  Strictly it indicates that the only way=20
to locate the child devices of this bus is by using the=20
address information in the device tree - there's no way to=20
dynamically probe the bus.

So if I understand correctly, "simple-bus" is intended to be used for
true buses.

=20
The fact that this causes of_platform_devices to be=20
instantiated is a Linux implementation specific detail (and=20
one we might change in future).

Here we have a common case for SoC that part of a device has its
separate driver besides the driver for the main feature of the whole
device.  The resources used by the sub-device is usually part of the
resources of the parent device.  So it makes sense to put the node of
sub-device beneathe the node of main device.  Shall we have a convention
to mark such devices in device tree so that the sub-device can be
scanned and probed as a standalone of_platform_device?

If "simple-bus" may cause confusion to do this job as it's not a bus
actually, I propose to use "has-subdevice".

- Leo