Re: [patch/rft 2.6.17-rc5-git 2/6] add PM_EVENT_PRETHAW

[David Brownell <david-b@pacbell.net>]

On Tuesday 30 May 2006 12:17 pm, Pavel Machek wrote:
> Hi!
> 
> Looks mostly good...
> 
> > This adds a new pm_message_t event type to use when preparing to switch
> > into a swsusp snapshot.  Devices that have been initialized by Linux
> > after resume (rather than left in power-up-reset state) may need to be
> > reset; this new event type gives drivers the chance to do that.
> > 
> > The drivers that will care about this are those which understand more
> > hardware states than just "on" and "reset", and read the hardware state
> > during resume().   ...
> 
> ...should this go to Documentation/ somewhere?

I have a separate doc patch, which I will send once the code passes
sufficient muster.


> > + * Other transitions are triggered by messages sent using suspend().  All
> > + * these transitions quiesce the driver, so that I/O queues are inactive.
> > + * That commonly entails turning off IRQs and DMA; there may be rules
> 
> Actually all DMAs must always be turned off. Otherwise swsusp can't
> get consistent image. IRQs can be disabled or not (they usually are), however driver
> prefers... but DMA must be off.

I think there are cases where DMA should still be active, but didn't want to
go into them.  For FREEZE, DMA should stop, yes.

Surely there'd be no point in **disllowing** system states where almost
everything is idled (CPU, most peripherals, etc) but the I/O is flowing?
Normally it's felt to be a _good_ thing to get the system into modes
like that.

- Dave