From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from gate.crashing.org (gate.crashing.org [63.228.1.57]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client did not present a certificate) by ozlabs.org (Postfix) with ESMTP id 3760D67DE9 for ; Sun, 31 Jul 2005 02:21:27 +1000 (EST) From: Benjamin Herrenschmidt To: Kevin Diggs In-Reply-To: <42E672B1.7050709@hypersurf.com> References: <42E672B1.7050709@hypersurf.com> Content-Type: text/plain Date: Sat, 30 Jul 2005 18:18:03 +0200 Message-Id: <1122740284.18835.87.camel@gaston> Mime-Version: 1.0 Cc: linuxppc-dev@ozlabs.org Subject: Re: preliminary 750GX PLL control patch List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Tue, 2005-07-26 at 10:28 -0700, Kevin Diggs wrote: > Hi, > > I've attached a patch that adds preliminary access to the HID1 > register in the 750GX (aka the PLL config register). The patch is > against 2.4.30. It has been lightly tested on a PowerMac 8600 with a > PowerLogix PowerForce 750GX cpu card. > > Depending on the values for the pllx_cfg field, this should > work on the 750FX as well ... except for the stuff in idle_6xx.S. Since > there are plenty of people on this list way more smarterer than me I was > hoping someone could answer a question about the powersave modes that > some of the PowerPC processors have: > > Since, as I understand it, the clock is shut off to much of the > chip when a powersave mode is engaged does it really buy you that much > to switch to a lower clock speed? Wouldn't you be better off shutting > off the unused PLL? > > Also, please note that I am not very experienced creating > patches so please use a backup of your source tree. Well... I replicated what darwin does here. I don't remember completely but it's possible that there is some kind of CPU errata related to nap and clock speed... or maybe it still makes a difference :) You want to wakeup fast from nap too, so switching off/on the unused PLL might not be that a good idea. But heh, you are welcome to try & measure. Ben.