[RFC] CPUFreq PowerOP integration, Intro 0/3

[RFC] CPUFreq PowerOP integration, Intro 0/3

[Eugeny S. Mints]

Integrating CPUFreq and PowerOP was discussed at the Linux PM summit
and in recent emails exchanges.  Some say keep them separate and some
say they must be integrated.  There is actually a very natural point
where integration makes sense - cpufreq_driver. This patchset presents
that integration point and is submitted for discussion.

The patches do not change the functionality of the cpufreq core.
Instead the idea is to redesign the tightly coupled interfaces of
cpufreq to clearly separate the arch dependent and independent pieces
layers.  This enables cpufreq to become arch independent and can start
to use the named operating points in all its layers.

PowerOP  replaces cpufreq driver as the h/w independent interface for
operating points.  PM core handles the h/w specific details for
defining the power parameters and setting the power parameters in h/w
registers.  Operating point definition/registration is now independent
of cpufreq.

Please note, that all userspace/kernel governor concepts, legacy sysfs cpufreq
interface remain untouched and SMP case is accounted in the resulting code as
well.

Highlights:

cpufreq.c
- get rid of cpufreq driver calls. the calls are replaced be calls to arch
independent freq_helpers (freq_helpers.c)
- available frequencies sysfs interface now can be handled in arch independent
way
- cpufreq_sysdev_driver now serves only cpufreq core internal needs upon cpu
add/remove events (since all hw related is handled by PM Core)
- cpufreq_powerop_call() is added to handle operating point registration in the
kernel by an independent module at arbitrary moment

freq_table.c (now freq_helpers.c)
- get rid of cpufreq_frequency_table structures as input parameter and made the
code arch independent by leveraging PowerOP interface
- routine remain the same but are no longer used by arch dependent code but by
cpufreq core arch independent code instead
- all routines are arch independent; the only shared knowledge is platform
power parameter names (string)
- target() method expects power parameter names "freqN", "vN" are supported by
PM Core for cpu N
- setpolisy() method expects power parameter names "hfreqN", "lfreqN", "vN" are
supported by PM Core for cpu N

Re: [RFC] CPUFreq PowerOP integration, Intro 0/3

[Dominik Brodowski]

Hi,

Just some nitpicking at the description, will cover the patches next.

On Thu, Sep 14, 2006 at 06:42:26PM +0400, Eugeny S. Mints wrote:
> Integrating CPUFreq and PowerOP was discussed at the Linux PM summit
> and in recent emails exchanges.  Some say keep them separate and some
> say they must be integrated.  There is actually a very natural point
> where integration makes sense - cpufreq_driver.

Well, I don't think that cpufreq_driver is the "natural" point -- in fact,
I think it is one of the worst points for the interaction. My alternative
suggestion will be the last one of the many mails you'll likely receive from
me today :)

> The patches do not change the functionality of the cpufreq core.
> Instead the idea is to redesign the tightly coupled interfaces of
> cpufreq to clearly separate the arch dependent and independent pieces
> layers.  This enables cpufreq to become arch independent and can start
> to use the named operating points in all its layers.

cpufreq is arch independent, as can be seen that it is used by many
different architectures right now.

> cpufreq.c
> - get rid of cpufreq driver calls. the calls are replaced be calls to arch
> independent freq_helpers (freq_helpers.c)

Have you considered the drivers which do not use the frequency table helper
library in cpufreq?

> - available frequencies sysfs interface now can be handled in arch 
> independent way

Also for the case where there are thousands of frequency states? Or only a
range to be set, and a in-CPU-mode [longrun]? There's a reason this export
is optional.

> - cpufreq_sysdev_driver now serves only cpufreq core internal needs upon cpu
> add/remove events (since all hw related is handled by PM Core)

That sounds like a good step forward -- especially as sysdevs may actually
be removed soon. It's orthogonal to the other changes though; i.e. we could
do that with the current cpufreq core without switching to PowerOP/"PM
core".

> freq_table.c (now freq_helpers.c)
> - get rid of cpufreq_frequency_table structures as input parameter and made 
> the code arch independent by leveraging PowerOP interface

arch independent? Well, this helper library is used by different archs already...

Thanks,
	Dominik