linux-kernel - RE: [PATCH 3/3] x86/tsc_msr: Make MSR derived TSC frequency more accurate

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Message-ID: <01feee20ee5d4b83ab218c14fc35accb@AcuMS.aculab.com>
Date:   Thu, 30 Jan 2020 16:02:30 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Hans de Goede' <hdegoede@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>
CC:     Andy Shevchenko <andy@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Vipul Kumar <vipulk0511@...il.com>,
        Vipul Kumar <vipul_kumar@...tor.com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Srikanth Krishnakar <Srikanth_Krishnakar@...tor.com>,
        Cedric Hombourger <Cedric_Hombourger@...tor.com>,
        Len Brown <len.brown@...el.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: RE: [PATCH 3/3] x86/tsc_msr: Make MSR derived TSC frequency more
 accurate

From: Hans de Goede
> Sent: 30 January 2020 15:55
...
> >> + * Moorefield (CHT MID) SDM MSR_FSB_FREQ frequencies simplified PLL model:
> >> + * 0000:   100 *  5 /  6  =  83.3333 MHz
> >> + * 0001:   100 *  1 /  1  = 100.0000 MHz
> >> + * 0010:   100 *  4 /  3  = 133.3333 MHz
> >> + * 0011:   100 *  1 /  1  = 100.0000 MHz
> >
> > Unless I'm going cross-eyed, that's 4 times the exact same table.
> 
> Correct, except that the not listed values on the none Cherry Trail
> table are undefined in the SDM, so we should probably deny them
> (or as the old code was doing simply return 0).
> 
> And at least the Moorefield (CHT MID) table is different for 0011, that
> is again 100 MHz like 0001 instead of 116.6667 as it is for BYT and CHT.
> 
> Note that the Merriefield (BYT MID) and Moorefield (CHT MID) values are
> based on the old code I've not seen those values in the current latest
> version of the SDM.

I wonder if Moorefield:11 is an old typo?

	David

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