Hi.
Perhaps we can help ourselves solidify this discussion a little by
producing some pseudo code. Here's my first hack at driver "fred". I
haven't made any effort at applying _all_ of the discussion so far. Feel
free to ignore it, pull it to pieces...
Nigel
/* fred_power_management
*
* Called on system state transitions and run time transitions
*/
static int fred_power_management(pm_messsage_t * request)
{
/* The state we're really in */
static int current_state = FRED_FULL_POWER;
/* The state we would be in if a system state isn't overriding us */
static int current_state_rt = FRED_FULL_POWER;
/*
* pm_message_to_fred_state might be the same function for a whole
* swag of devices eg those on a particular bus
*/
int fred_state_requested = pm_message_to_fred_state(request);
int result = 0;
/*
* Whether a system state or rt state requested, if we're
* already in the state, there's nothing to do.
*/
if (fred_state_requested == current_state)
return 0;
if (request->type == PM_SYSTEM_STATE) {
/* Can we, and do we want to decline the transition? */
if (request->can_decline && i_dont_want_to())
return -ENO_WAY_HOSE;
} else {
current_state_rt = fred_state_requested;
/* Does system state force us to a lower state? */
if (current_state < fred_state_requested)
return 0;
}
/*
* Perhaps other drivers (not necessarily parent) might like to know
* I'm about to change state. They might also want to say "Don't do it!"
* Is a notifier chain the best way to do this?
* notifier_chain (or whatever) would really be part of the struct device,
* I guess.
*/
if (result=notifier_call_chain(&fred_pre_state_change_notifier_chain))
return result;
switch (fred_state_requested) {
case FRED_FULL_POWER:
/* whatever is required to do the transition */
break;
case FRED_SEMI_CONSCIOUS:
/* whatever is required to do this transition */
break;
}
/*
* Perhaps other drivers (not necessarily parent) might like to know
* I have changed state. They can't complain now, though.
*/
notifier_call_chain(&fred_post_state_change_notifier_chain))
current_state = fred_state_requested;
return 0;
}
--
Nigel Cunningham
Software Engineer, Canberra, Australia
http://www.cyclades.com
Bus: +61 (2) 6291 9554; Hme: +61 (2) 6292 8028; Mob: +61 (417) 100 574
Maintainer of Suspend2 Kernel Patches http://suspend2.net
