Re: [linux-pm] [PATCH] Custom power states for non-ACPI systems

[Todd Poynor <tpoynor@mvista.com>]

Pavel Machek wrote:
...
>>In most of the cases I'm thinking of, it wouldn't be a user 
>>requesting a state but rather software (say, a cell phone 
>>progressively entering lower power states due to inactivity).  I 
>>haven't noticed a platform with more than 3 low-power modes so far, 
> 
> 
> Are not your power states more like cpu power states?
> These are expected to be system states, and sleeping system
> does not take calls, etc...

There's a great variety of behaviors and usage models out there, not 
sure I can draw a useful distinction between cpu power states vs. system 
states, but the net effect could be considered to be approximately the 
same in typical embedded uses: the drivers are called to place 
appropriate devices in a low(er)-power state, various platform thingies 
are slowed or powered off, and the system stops waiting for something to 
wake it up.  In some cases the system does not wake up until an explicit 
user action (button press, etc.), but more commonly 
wake-on-device-activity (including ring from telephony unit) or 
time-based actions (including wake on alarm from event in user's 
datebook) is also wanted (rather like wake-on-LAN et al).  I don't think 
this would correspond well to hardware-managed CPU power states like 
ACPI C states, for example.  Thanks,


-- 
Todd