Using out of band messages to change min/max frequencies

Using out of band messages to change min/max frequencies

[Mark Langsdorf]

Does cpufreq currently support having an out-of-band agent
change the available minimum/maximum frequency and then
have the current frequency conform to the new values?

I experimented with a notifier routine (from an IPC
context) that used cpufreq_get_policy() and
cpufreq_update_policy(). I ran into two problems:
1) cpufreq_update_policy() would overwrite the
changes I made to the minimum/maximum settings
2) the driver->target call would be called within
the notifier context, and would explode when it
called its own notifiers.

driver->bios_limit doesn't seem like the right answer,
since it wouldn't be called if the current governor
has a static policy (ie performance, powersave).

Is there some better way to approach this? Ideally,
I'd like something like the ACPI _PPC concept, but
looking over that code I'm not sure it actually
limits the frequency correctly.

--Mark Langsdorf
Calxeda, Inc.

Re: Using out of band messages to change min/max frequencies

[Antti P Miettinen]

Mark Langsdorf <mark.langsdorf@calxeda.com> writes:
> Is there some better way to approach this?

PM QoS :-)

http://thread.gmane.org/gmane.linux.kernel.cpufreq/7794
http://thread.gmane.org/gmane.linux.kernel.cpufreq/7797

	--Antti

Re: Using out of band messages to change min/max frequencies

[Mark Langsdorf]

On 03/16/2012 01:26 PM, Antti P Miettinen wrote:
> Mark Langsdorf <mark.langsdorf@calxeda.com> writes:
>> Is there some better way to approach this?
> 
> PM QoS :-)
> 
> http://thread.gmane.org/gmane.linux.kernel.cpufreq/7794
> http://thread.gmane.org/gmane.linux.kernel.cpufreq/7797

Thanks, that looks like it could be useful.

Is there a sample implementation of this in the context of
a cpufreq device driver?

--Mark Langsdorf
Calxeda, Inc.

Re: Using out of band messages to change min/max frequencies

[Antti P Miettinen]

Mark Langsdorf <mark.langsdorf@calxeda.com> writes:
> On 03/16/2012 01:26 PM, Antti P Miettinen wrote:
>> Mark Langsdorf <mark.langsdorf@calxeda.com> writes:
>>> Is there some better way to approach this?
>> 
>> PM QoS :-)
>> 
>> http://thread.gmane.org/gmane.linux.kernel.cpufreq/7794
>> http://thread.gmane.org/gmane.linux.kernel.cpufreq/7797
>
> Thanks, that looks like it could be useful.
>
> Is there a sample implementation of this in the context of
> a cpufreq device driver?

Hmm.. controlling cpufreq core from cpufreq driver? Nope, this input
event booster is the only example I have:

http://thread.gmane.org/gmane.linux.kernel.cpufreq/7801

	--Antti

Re: Using out of band messages to change min/max frequencies

[Mark Langsdorf]

On 03/18/2012 09:34 AM, Antti P Miettinen wrote:
> Mark Langsdorf <mark.langsdorf@calxeda.com> writes:
>> On 03/16/2012 01:26 PM, Antti P Miettinen wrote:
>>> Mark Langsdorf <mark.langsdorf@calxeda.com> writes:
>>>> Is there some better way to approach this?
>>>
>>> PM QoS :-)
>>>
>>> http://thread.gmane.org/gmane.linux.kernel.cpufreq/7794
>>> http://thread.gmane.org/gmane.linux.kernel.cpufreq/7797
>>
>> Thanks, that looks like it could be useful.
>>
>> Is there a sample implementation of this in the context of
>> a cpufreq device driver?
> 
> Hmm.. controlling cpufreq core from cpufreq driver? Nope, this input
> event booster is the only example I have:
> 
> http://thread.gmane.org/gmane.linux.kernel.cpufreq/7801

Thanks. It wasn't exactly applicable, but it gave enough
hints that I got the QoS parts working for my driver.

--Mark Langsdorf
Calxeda, Inc.