linux-kernel - Re: [RFC PATCH] platform: Faciliatate the creation of pseduo-platform busses

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Message-ID: <4C58B1B6.9050005@quicinc.com>
Date:	Tue, 3 Aug 2010 17:17:58 -0700
From:	Patrick Pannuto <ppannuto@...cinc.com>
To:	Greg KH <gregkh@...e.de>
CC:	Patrick Pannuto <ppannuto@...eaurora.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-msm@...r.kernel.org" <linux-arm-msm@...r.kernel.org>,
	"linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>,
	"damm@...nsource.se" <damm@...nsource.se>,
	"lethal@...ux-sh.org" <lethal@...ux-sh.org>,
	"rjw@...k.pl" <rjw@...k.pl>, "dtor@...l.ru" <dtor@...l.ru>,
	"eric.y.miao@...il.com" <eric.y.miao@...il.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [RFC PATCH] platform: Faciliatate the creation of pseduo-platform
 busses

>>>>
>>>> 	struct platform_device sub_bus1 = {
>>>> 		.name		= "sub_bus1",
>>>> 		.id		= -1,
>>>> 		.dev.bus	= &my_bus_type,
>>>> 	}
>>>> 	EXPORT_SYMBOL_GPL(sub_bus1);
>>>
>>> You really want a bus hanging off of a bus?  Normally you need a device
>>> to do that, which is what I think you have here, but the naming is a bit
>>> odd to me.
>>>
>>> What would you do with this "sub bus"?  It's just a device, but you are
>>> wanting it to be around for something.
>>>
>>
>> It's for power management stuff, basically, there are actual physical buses
>> involved that can be completely powered off IFF all of their devices are
>> not in use. Plus it actually matches bus topology this way.
> 
> Then create a real bus hanging off of a device, not another device that
> "acts" like a bus here, right?  Or am I missing the point?
> 

The motivation for doing it this was is that one driver could drive
devices on two different subbusses.  In the example, "my-driver" could
drive a device on sub_bus1 AND sub_bus2 (if there were 2+ devices, one
or more on each bus).

>From my understanding, this is not possible if they are actually
different busses.
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