Re: [PATCH 01/13] OMAP: Introduce a user list for each voltage domain instance in the voltage driver.

[Nishanth Menon <nm@ti.com>]

Thomas Petazzoni had written, on 09/02/2010 02:43 AM, the following:
> Hello,
> 
> On Wed, 01 Sep 2010 15:51:40 -0700
> Kevin Hilman <khilman@deeprootsystems.com> wrote:
> 
>> Looking closer at this, keeping track of a list of devices and
>> constraints is what the regulator framework does as well.  
>>
>> Before we get too far down this path, we need to start working with
>> Thomas Petazzoni to better understand how we can use the regulator
>> framework for much of the management levels of the voltage layer.
> 
> Yes, as discussed on IRC with Kevin, I think that some of this voltage
> layer mechanisms would benefit from using the existing kernel regulator
> framework.
> 
> The regulator framework already keeps tracks of consumers (in your
> patch set called "vdd users"), and for each consumer, keeps track of
> the requested voltage. The maximum requested voltage is then applied to
> the regulator. It seems to fit quite well some of the mechanisms you're
> introducing in this patch set.

Just brainstorming -> if we use the regulator framework - there are 
potential benefits - agreed. BUT, consider the cpuidle path -> currently 
we disable SR while hitting off/ret for class3, this is done in irq 
locked context while the regulator framework uses locks by itself - we 
would probably have to evolve an entirely different mechanism to handle 
this.

SR by itself can easily be represented I believe and my thoughts  when i 
initialy looked at that option had been:
a) latency overheads
b) flexibility we achieve vs complexity in s/w implementation
c) lock handling - esp impact on omap_sram_idle paths..

-- 
Regards,
Nishanth Menon

PS:personally though concept of latency additions when scaling voltages, 
disabling SR etc should be a parameter in userspace governor decisions 
(the fact that cpuidle and cpufreq are independent statemachine is not 
my personal fav either). But this is a larger topic of discussion not 
pertinent to this thread..