On Tue, Aug 03, 2010 at 05:02:29PM -0700, Patrick Pannuto wrote:
> On 08/03/2010 04:56 PM, Greg KH wrote:
> > On Tue, Aug 03, 2010 at 04:35:06PM -0700, Patrick Pannuto wrote:
> >> Inspiration for this comes from:
> >> http://www.mail-archive.com/[email protected]/msg31161.html
> >>
> >> INTRO
> >>
> >> As SOCs become more popular, the desire to quickly define a simple,
> >> but functional, bus type with only a few unique properties becomes
> >> desirable. As they become more complicated, the ability to nest these
> >> simple busses and otherwise orchestrate them to match the actual
> >> topology also becomes desirable.
> >>
> >> EXAMPLE USAGE
> >>
> >> /arch/ARCH/MY_ARCH/my_bus.c:
> >>
> >> #include <linux/device.h>
> >> #include <linux/platform_device.h>
> >>
> >> struct bus_type my_bus_type = {
> >> .name = "mybus",
> >> };
> >> EXPORT_SYMBOL_GPL(my_bus_type);
For your question below, this could be in write-only memory. Well, I
guess it never is as we modify things in the bus structure, so nevermind
about that, false alarm.
> >>
> >> 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?
> >> +void platform_bus_type_init(struct bus_type *bus)
> >> +{
> >> + if (!bus->dev_attrs)
> >> + bus->dev_attrs = platform_bus_type.dev_attrs;
> >> + if (!bus->match)
> >> + bus->match = platform_bus_type.match;
> >> + if (!bus->uevent)
> >> + bus->uevent = platform_bus_type.uevent;
> >> + if (!bus->pm)
> >> + bus->pm = platform_bus_type.pm;
> >
> > Watch out for things in "write only" memory here. That could cause
> > problems.
>
> Pardon my ignorance (I'm quite new to kernel work), what do you mean
> here? What memory could be "write only"?
See above. I was thinking that struct bus would be a constant or
something. Sorry.
greg k-h
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