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Message-ID: <87lgigdo5f.fsf@concordia.ellerman.id.au> Date: Wed, 06 Dec 2017 23:41:32 +1100 From: Michael Ellerman <mpe@...erman.id.au> To: Gautham R Shenoy <ego@...ux.vnet.ibm.com> Cc: Shilpasri G Bhat <shilpa.bhat@...ux.vnet.ibm.com>, linux-pm@...r.kernel.org, "Gautham R. Shenoy" <ego@...ux.vnet.ibm.com>, viresh.kumar@...aro.org, rjw@...ysocki.net, linux-kernel@...r.kernel.org, huntbag@...ux.vnet.ibm.com, linuxppc-dev@...ts.ozlabs.org, akshay.adiga@...ux.vnet.ibm.com Subject: Re: [PATCH] cpufreq: powernv: Define methods to parse positive & negative pstates Gautham R Shenoy <ego@...ux.vnet.ibm.com> writes: > Hi Michael, > > On Wed, Dec 06, 2017 at 09:54:27PM +1100, Michael Ellerman wrote: >> Shilpasri G Bhat <shilpa.bhat@...ux.vnet.ibm.com> writes: >> >> > From: "Gautham R. Shenoy" <ego@...ux.vnet.ibm.com> >> > >> > 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
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