[linux-dvb] Re: refactoring

[Andrew de Quincey <adq_dvb@lidskialf.net>]

On Monday 11 Oct 2004 13:20, Andrew de Quincey wrote:
> On Monday 11 Oct 2004 13:14, Johannes Stezenbach wrote:
> > On Mon, Oct 11, 2004 at 12:32:45PM +0100, Andrew de Quincey wrote:
> > > On Monday 11 Oct 2004 12:29, Johannes Stezenbach wrote:
> > > > Well, if the i2c bus and the devices on the bus aren't exposed
> > > > at all in sysfs, then the DVB adapter driver could take care
> > > > of it when called via PCI bus power management hooks. I don't
> > > > think this is a good design, but it would work for PCI cards.
> > >
> > > I'm only talking about not exposing the bits of the frontend - exposing
> > > the i2c bus is fine - you might have self-contained devices on it that
> > > it makes sense for userspace to see (e.g. EEPROMs, analogue tv tuners).
> >
> > Then I suspect we might run into problems when the power management
> > core decides to power down busses in the wrong order. Well, on PCI
> > cards one could make the i2c adapter shutdown a noop, and do the i2c
> > shutdown when the PCI adapter is shutdown. On embedded you have
> > no such luck. You must power down the demod/PLL before the
> > i2c bus goes to sleep. (There'll be probable ways to kludge
> > around this, but it will never be clean&simple.)
>
> Urgh, there is no nice solution to this. What is the least nasty?

For that matter, how do you control the order in which i2c devices on a single 
bus are shut down? You'd have to shut down the PLL before the demod, in order 
to be able to use the demod's i2c bus switch.