[linux-dvb] Re: refactoring

[Gerd Knorr <kraxel@bytesex.org>]

On Mon, Oct 11, 2004 at 01:26:04PM +0100, Andrew de Quincey wrote:
> > > 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.

My cx22702 driver does the suspend/resume simply in the demod
powermanagement handlers.  Code isn't tested yet through, I'm somehow
too busy writing mails these days ...

The ordering of the devices within the bus doesn't matter.  The
important point is that the ordering of the devices and the bus itself
is correct (i.e. first suspend the i2c devices, then the PCI (or
whatever) device the i2c bus is connected through).  Thus you can be
sure you can access the i2c bus within the suspend/resume handlers.

  Gerd

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