Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752310AbdLFMli (ORCPT ); Wed, 6 Dec 2017 07:41:38 -0500 Received: from ozlabs.org ([103.22.144.67]:35905 "EHLO ozlabs.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751840AbdLFMle (ORCPT ); Wed, 6 Dec 2017 07:41:34 -0500 From: Michael Ellerman To: Gautham R Shenoy Cc: Shilpasri G Bhat , linux-pm@vger.kernel.org, "Gautham R. Shenoy" , viresh.kumar@linaro.org, rjw@rjwysocki.net, linux-kernel@vger.kernel.org, huntbag@linux.vnet.ibm.com, linuxppc-dev@lists.ozlabs.org, akshay.adiga@linux.vnet.ibm.com Subject: Re: [PATCH] cpufreq: powernv: Define methods to parse positive & negative pstates In-Reply-To: <20171206111944.GB22880@in.ibm.com> References: <1512017018-4857-1-git-send-email-shilpa.bhat@linux.vnet.ibm.com> <87r2s8dt3w.fsf@concordia.ellerman.id.au> <20171206111944.GB22880@in.ibm.com> Date: Wed, 06 Dec 2017 23:41:32 +1100 Message-ID: <87lgigdo5f.fsf@concordia.ellerman.id.au> MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1460 Lines: 40 Gautham R Shenoy writes: > Hi Michael, > > On Wed, Dec 06, 2017 at 09:54:27PM +1100, Michael Ellerman wrote: >> Shilpasri G Bhat writes: >> >> > From: "Gautham R. Shenoy" >> > >> > Pstates are 8bit values but on POWER8 they are negative and on POWER9 >> > they are positive. This patch adds helper routines to differentiate >> > the sign to read the correct pstate value. >> >> This sounds like it could be a bad bug, but I can't really tell from the >> change log. What is the actual impact of not having this patch? > > On some POWER9 platforms, there can be more than 128 pstates. > > Without this patch, on such platforms, if the value of the current > frequency corresponds to a pstate greater than 128, then the code will > interpret it as a negative number, and report that the "pstate is out > of bound" while returning a nominal frequency. OK, that's good detail to have in the change log, please include it. >> Should it have a Fixes/Cc-stable tag? > > This doesn't fix any prior commit, but is fixes a newly discovered > bug. OK. You could say it "fixes" the commit that added Power9 support to the driver, but it seems there wasn't really a commit that did that specifically. > I will resend the patch Cc'ing stable. You don't have to Cc stable, that was just a suggestion. Though it sounds like the symptoms are probably bad enough to warrant it. cheers