From mboxrd@z Thu Jan 1 00:00:00 1970 From: Gautham R Shenoy Subject: Re: [v3 PATCH 1/3] powernv-cpufreq: Add helper to extract pstate from PMSR Date: Mon, 18 Dec 2017 14:33:19 +0530 Message-ID: <20171218090319.GC28881@in.ibm.com> References: <1513148261-21097-1-git-send-email-ego@linux.vnet.ibm.com> <1513148261-21097-2-git-send-email-ego@linux.vnet.ibm.com> Reply-To: ego@linux.vnet.ibm.com Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org To: Balbir Singh Cc: "Gautham R. Shenoy" , Shilpasri G Bhat , Viresh Kumar , "Rafael J. Wysocki" , huntbag@linux.vnet.ibm.com, Akshay Adiga , Michael Ellerman , Vaidyanathan Srinivasan , linux-pm@vger.kernel.org, "linux-kernel@vger.kernel.org" , "open list:LINUX FOR POWERPC (32-BIT AND 64-BIT)" List-Id: linux-pm@vger.kernel.org Hi Balbir, On Sun, Dec 17, 2017 at 02:04:03PM +1100, Balbir Singh wrote: > On Wed, Dec 13, 2017 at 5:57 PM, Gautham R. Shenoy > wrote: > > From: "Gautham R. Shenoy" > > > > On POWERNV platform, the fields for pstates in the Power Management > > Status Register (PMSR) and the Power Management Control Register > > (PMCR) are 8-bits wide. On POWER8 the pstates are negatively numbered > > while on POWER9 they are positively numbered. > > > > The device-tree exports pstates as 32-bit entries. The device-tree > > implementation sign-extends the 8-bit pstate values to obtain the > > corresponding 32-bit entry. > > > > Eg: On POWER8, a pstate value 0x82 [-126] is represented in the > > device-tree as 0xfffffff82 while on POWER9, the same value 0x82 [130] > > is represented in the device-tree as 0x00000082. > > > > The powernv-cpufreq driver implementation represents pstates using the > > integer type. In multiple places in the driver, the code interprets > > the pstates extracted from the PMSR as a signed byte and assigns it to > > a integer variable to get the sign-extention. > > > > On POWER9 platforms which have greater than 128 pstates, this results > > in the driver performing incorrect sign-extention, and thereby > > treating a legitimate pstate (say 130) as an invalid pstates (since it > > is interpreted as -126). > > > > This patch fixes the issue by implementing a helper function to > > extract Pstates from PMSR register, and correctly sign-extend it to be > > consistent with the values provided by the device-tree. > > > > Signed-off-by: Gautham R. Shenoy > > --- > > This looks better Thanks for the Review. > > Acked-by: Balbir Singh > > Balbir Singh >