Re: [PATCH 3/3] x86/tsc_msr: Make MSR derived TSC frequency more accurate

[Hans de Goede]

Hi,

On 30-01-2020 17:02, David Laight wrote:
> 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?

I have no idea. Andy if you can find any docs on the MSR_FSB_FREQ values
for Merriefield (BYT MID) and Moorefield (CHT MID) that would be great,
if not I suggest we stick with what we have.

Regards,

Hans