Main differences between drivers

Main differences between drivers

[Guilherme Moro]

Hello all,

Can someone explain, or send a link or a document that explain the
real difference between the different drivers for Intel processors ?
Why the same processor can use speedstep-ich, speedstep-centrino and
acpi-cpufreq ?
the basic differences I can understand, like acpi-cpufreq use of acpi
tables, but what driver is the "better" or more "official" for Intel
platforms?

Guilherme Moro

Re: Main differences between drivers

[Len Brown]

On Tuesday 15 August 2006 10:22, Guilherme Moro wrote:
> Hello all,
> 
> Can someone explain, or send a link or a document that explain the
> real difference between the different drivers for Intel processors ?
> Why the same processor can use speedstep-ich, speedstep-centrino and
> acpi-cpufreq ?
> the basic differences I can understand, like acpi-cpufreq use of acpi
> tables, but what driver is the "better" or more "official" for Intel
> platforms?

good question -- the names are quite poor, and unfortunately
it is a pain to re-name drivers.

As of 2.6.17, both acpi-cpufreq and speedstep-centrino 
use ACPI tables, but acpi-cpufreq uses IO accesses
and speedstep centrino uses MSR accesses. 
Since MSR accesses are faster,
it is preferred to try speedstep-centrino first.

speedstep centrino also has reverse engineered tables to fall back on
if ACPI tables fail.  I haven't seen this happen in practice in recent history.
The hard-coded tables were there from before Intel published the PDC
bits that allow ACPI tables to work with MSR accesses.

Going forward, there has been a set of patches on the list to:
1. add MSR access to acpi-cpufreq
2. remove ACPI tables from speedstep-centrino.

That would mean that acpi-cpufreq can handle any ACPI situation --
IO or MSR; and that speedstep-centrino would be only for the reverse-engineered case.
Thus the preference would change to be acpi-cpufreq first, speedstep-centrino second --
though the reverse preference would probably be okay too.

-Len

ps. don't bother with speedstep-ich if the above work, and never use p4-clockmod.

RE: Main differences between drivers

[Guilherme Moro]

Hello again

Another question, this 2 drivers can, theorically, cover all kind of Intel
based hardware?
If I build my own, all new, platform, will I need to write a new driver?
Will emerge any situation to write a new driver, thinking that I will always
use Intel processors, compatibles with Enhanced SpeedStep?

Guilherme Moro

> -----Mensagem original-----
> De: Len Brown [mailto:len.brown@intel.com]
> Enviada em: Tuesday, August 15, 2006 11:57 AM
> Para: cpufreq@lists.linux.org.uk
> Cc: Guilherme Moro
> Assunto: Re: Main differences between drivers
>
> On Tuesday 15 August 2006 10:22, Guilherme Moro wrote:
> > Hello all,
> >
> > Can someone explain, or send a link or a document that explain the
> > real difference between the different drivers for Intel processors ?
> > Why the same processor can use speedstep-ich, speedstep-centrino and
> > acpi-cpufreq ?
> > the basic differences I can understand, like acpi-cpufreq use of acpi
> > tables, but what driver is the "better" or more "official" for Intel
> > platforms?
>
> good question -- the names are quite poor, and unfortunately
> it is a pain to re-name drivers.
>
> As of 2.6.17, both acpi-cpufreq and speedstep-centrino
> use ACPI tables, but acpi-cpufreq uses IO accesses
> and speedstep centrino uses MSR accesses.
> Since MSR accesses are faster,
> it is preferred to try speedstep-centrino first.
>
> speedstep centrino also has reverse engineered tables to fall back on
> if ACPI tables fail.  I haven't seen this happen in practice in recent
> history.
> The hard-coded tables were there from before Intel published the PDC
> bits that allow ACPI tables to work with MSR accesses.
>
> Going forward, there has been a set of patches on the list to:
> 1. add MSR access to acpi-cpufreq
> 2. remove ACPI tables from speedstep-centrino.
>
> That would mean that acpi-cpufreq can handle any ACPI situation --
> IO or MSR; and that speedstep-centrino would be only for the reverse-
> engineered case.
> Thus the preference would change to be acpi-cpufreq first, speedstep-
> centrino second --
> though the reverse preference would probably be okay too.
>
> -Len
>
> ps. don't bother with speedstep-ich if the above work, and never use p4-
> clockmod.
>
>
> --
> No virus found in this incoming message.
> Checked by AVG Free Edition.
> Version: 7.1.405 / Virus Database: 268.10.10/419 - Release Date: 8/15/2006
>

--
No virus found in this outgoing message.
Checked by AVG Free Edition.
Version: 7.1.405 / Virus Database: 268.10.10/419 - Release Date: 8/15/2006


--
No virus found in this outgoing message.
Checked by AVG Free Edition.
Version: 7.1.405 / Virus Database: 268.10.10/419 - Release Date: 8/15/2006




-- 
Guilherme Moro

RE: Main differences between drivers

[Pallipadi, Venkatesh]

 

>-----Original Message-----
>From: cpufreq-bounces@lists.linux.org.uk 
>[mailto:cpufreq-bounces@lists.linux.org.uk] On Behalf Of Guilherme Moro
>Sent: Tuesday, August 15, 2006 11:44 AM
>To: cpufreq@lists.linux.org.uk
>Subject: RE: Main differences between drivers
>
>Hello again
>
>Another question, this 2 drivers can, theorically, cover all 
>kind of Intel
>based hardware?
>If I build my own, all new, platform, will I need to write a 
>new driver?
>Will emerge any situation to write a new driver, thinking that 
>I will always
>use Intel processors, compatibles with Enhanced SpeedStep?
>

Yes. They cover all the current hardware. In future the plan is to
combine the functionality under one driver instead of two. You don't
have to write a new driver as long as you have current Intel CPUs and
your platform provides ACPI support for Enhanced speedstep.

Thanks,
Venki