Re: powernow-k8 updates

From: Dominik Brodowski <linux@dominikbrodowski.de>
To: Pavel Machek <pavel@ucw.cz>
Cc: paul.devriendt@amd.com, Cpufreq mailing list <cpufreq@www.linux.org.uk>
Subject: Re: powernow-k8 updates
Date: Fri, 26 Mar 2004 14:02:54 +0100	[thread overview]
Message-ID: <20040326130254.GA9284@dominikbrodowski.de> (raw)
In-Reply-To: <20040326123216.GB321@elf.ucw.cz>

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On Fri, Mar 26, 2004 at 01:32:16PM +0100, Pavel Machek wrote:
> On Pá 26-03-04 13:27:42, Dominik Brodowski wrote:
> > On Fri, Mar 26, 2004 at 01:19:15PM +0100, Pavel Machek wrote:
> > > Hi!
> > > 
> > > > Few updates, enable ACPI, add common printing function, fix typo, move
> > > > "pst out of sequence" where it belongs, fix formating in
> > > > powernow-k8.h. I'm not quite sure what this is against, so this is
> > > > "eyes only".
> > > 
> > > Its strange, ACPI code does not seem to mention batps at all, still
> > > cpu goes to 800MHz when I unplug the cord... Perhaps it should at
> > > least say something into the syslog?
> > 
> > ... again our differences about verbosity... :-)
> 
> Actually, I do not understand how it works. How does cpufreq know how
> many states are there on battery? It does something, but I'd like to
> understand it...

The BIOS notifies the acpi processor module of a platform limit change
(acpi_processor_notify). The acpi processor module then reads out the _PDC
value of the ACPI table, which contains the maximum current supported
P-State [P0 is highest freq, Px is lowest]. 

Then the cpufreq_update_policy() function is called: the last cpufreq policy
set is send to the cpufreq notifiers, among them is
acpi_processor_ppc_notifier(), which limits the max allowed frequency, see

        cpufreq_verify_within_limits(policy, 0,
                pr->performance->states[ppc].core_frequency * 1000);

Then the policy (min/max frequency) is passed to a cpufreq governor [in most 
cases the userspace governor], which selects one speed between min and max 
frequency and tells the driver via ->target() of the frequency to set.

Hope this clarifies,

	Dominik

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