Multiple parents in device driver model and Common Display Framework (CDF)

[Greg KH]

On Tue, Feb 12, 2013 at 11:20:04PM +0100, Marcus Lorentzon wrote:
> Den 12 feb 2013 23:02 skrev "Greg KH" <gregkh at linuxfoundation.org>:
> >
> > On Tue, Feb 12, 2013 at 04:04:53PM +0100, Marcus Lorentzon wrote:
> > > 3) Daniel V hinted that multiple parents (or multiple busses) is
> > > something that has been discussed as a limitation of device driver
> > > model before. And that maybe now was the time to fix that or at
> > > least sort out how to handle it.
> >
> > No, it's the other way around, we have discussed ways about having
> > multiple drivers control a single device at the same time.  The
> > "multiple parents" issue has come up a number of times with the power
> > management people, but they solved this by keeping a separate tree of
> > how to properly control and walk things to handle power domains and the
> > like.
> >
> Thanks,
> does this mean there are no other devices in the kernel that sit on multiple
> busses that can be use as inspiration?

Lots of devices do this, but they all have an individual 'struct device'
for the part that sits on each bus, with a single driver controlling
both of them

> Was the discussion about handling one device from multiple drivers concluded/
> implemented? It sounds very much what we are trying to do? Or this was just
> some f2f discussion?

We've been talking about it off and on for many years now, and I think
the framework in the driver core is almost there, but in reality, the
different "types" of devices usually solve this problem, so we've never
spent the time to do anything else here.

sorry,

greg k-h