From mboxrd@z Thu Jan 1 00:00:00 1970 From: Len Brown Subject: Re: voltage tables Date: Mon, 30 Jul 2007 22:41:29 -0400 Message-ID: <200707302241.29635.lenb@kernel.org> References: <20070730230439.GB6949@tatooine.rebelbase.local> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20070730230439.GB6949@tatooine.rebelbase.local> Content-Disposition: inline List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: cpufreq-bounces@lists.linux.org.uk Errors-To: cpufreq-bounces+glkc-cpufreq=m.gmane.org+glkc-cpufreq=m.gmane.org@lists.linux.org.uk Content-Type: text/plain; charset="us-ascii" To: cpufreq@lists.linux.org.uk On Monday 30 July 2007 19:04, markus reichelt wrote: > Hi, > > just a thought.... with more and more people wondering why cpufreq > doesn't work on their over/underclocked systems, what about offering > the possibility to use static (and thus easily tweakable) voltage > tables instead of/parallel to the ACPI-approach? > > I don't know about the effort this would take to implement / the > stress it would put on maintenance, but it would be my choice. > > I'm thinking along the lines of using the ACPI values by default but > providing the means to use custom tables instead, for "experts". > > Given the slim chances (yes, I'm brainstorming) of success, what > about documentation -- if one would like to look into the matter and > try to implement the above? Anything apart from reading the source > code? Trying to speak for Intel parts only here, since I don't know what AMD does... In the past, there were model specific encoding for the bit pattern that got written to PERF_CTL. That is how speedstep-centrino was born. But these tables were a PITA to maintain, since they were not necessarily documented, and every stepping might have different encodings. Intel then documented the model-specific _PDC bits, which allowed open source to do this the way Windows does -- by asking ACPI. Thus acpi-cpufreq became the driver of choice, and speedstep-centrino was deprecated. Going forward, I believe that the hardware guys have no plans to maintain any sort of reasonable compatibility or even straightforward decoding of the bit pattern that gets written to PERF_CTL -- so the reason that speedstep-centrino and its hard-coded tables became deprecated will be even more true in the future. Further, I've not played with this, but my understanding is that on the Extreme parts, the way to over-clock them is to have a really good cooling solution, and then just enter the BIOS SETUP and select a higher maximum bus/core ratio. In theory, this should be reflected in the ACPI BIOS P-state tables, the tables should have accurate encodings for the necessary voltage, and assuming the cooling works, everybody is happy. Maybe somebody on the list can comment on if this last part works for them. I don't know b/c I never over-clock the parts -- I just use next year's parts:-) cheers, -Len