Re: community PM requirements/issues and PowerOP [Was: Re: So, what's the status on the recent patches here?]

["Eugeny S. Mints" <eugeny.mints@gmail.com>]

Pavel Machek wrote:
>>>> - PowerOP is only one layer (towards the bottom) in a power management 
>>>> solution.
>>>> - PowerOP does *not* replace cpufreq
>>> PowerOP provides userland interface for changing processor
>>> frequency. That's bad -- duplicate interface.
>> Basically the biggest problem with cpufreq interface is that cpufreq has 
>> "chose
>> predefined closest to a given frequency" functionality implemented in the
>> kernel while there is _no_ any reason to have this functionality 
>> implemented in
>> the kernel if we have sysfs interface exported by PowerOP in place - you 
>> just
> 
> No, there is reason to keep that in kernel -- so that cpufreq
> userspace interface can be kept, and so that resulting kernel<->user
> interface is not ugly.
Cpuferq defines cpufreq_frequency_table structure in arch independent header 
while it's arch dependent data structure. A lot of code is built around this 
invalid basic brick and therefore is invalid: cpufreq tables, interface with cpu 
freq drivers, etc. Notion of transition latency as it defined by cpufreq is 
wrong because it's not a function of cpu type but function of current and next 
operating point. no runtime control on operating points set. it's always the 
same set of operating points for all system cpus in smp case and no way to 
define different sets or track any dependencies in case say multi core cpus. 
insufficient kernel<->user space interface to handle embedded requirements and 
no way to extend it within current design. Shall I continue?  Why should then 
anyone want to keep cpufreq userspace interface just due to keep it?
> 
>> of the fact that cpufreq implements incorrect design of PM stack layers and
>> interfaces. PowerOP solves this issues as well.
> 
> Actually I believe that cpufreq implements correct design and PowerOP
> got it wrong.
PowerOP/cufreq integration patch set contains very details explanation of the 
cpufreq design issues and POwerOP solutions. Comment there is you feel it's wrong.

Eugeny
> 
>>> Well, you'll only get good interface review when you have
>>> Documentation/ , and it needs to go to lkml before it goes to any
>>> queues.
>> PM stack is too complex and heavy part to go in such pieces thru lkml. i 
>> expect all linux  pm experts to be on this list
> 
> "We are too lazy to make the code clean enough / well enough explained
> to survive lkml review".
> 
> Your interface impacts everyone, so everyone should have chance to
> comment on it.
> 								Pavel