linux-kernel - Re: [v3] x86/tsc: Unset TSC_KNOWN_FREQ and TSC

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Message-ID: <87imku2t3w.fsf@nanos.tec.linutronix.de>
Date:   Wed, 29 Jan 2020 16:13:39 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Hans de Goede <hdegoede@...hat.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     vipul kumar <vipulk0511@...il.com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        linux-kernel@...r.kernel.org, Stable <stable@...r.kernel.org>,
        Srikanth Krishnakar <Srikanth_Krishnakar@...tor.com>,
        Cedric Hombourger <Cedric_Hombourger@...tor.com>,
        x86@...nel.org, Len Brown <len.brown@...el.com>,
        Vipul Kumar <vipul_kumar@...tor.com>
Subject: Re: [v3] x86/tsc: Unset TSC_KNOWN_FREQ and TSC_RELIABLE flags on Intel Bay Trail SoC

Hans de Goede <hdegoede@...hat.com> writes:
> On 29-01-2020 15:14, Andy Shevchenko wrote:
>>> The only one which is possibly suspicious here is this line:
>>>
>>>   * 0111:   25 * 32 /  9  =  88.8889 MHz
>>>
>>> The SDM says 88.9 MHz for this one.

I trust math more than the SDM :)

>> Anyway it seems need to be fixed as well.
>> 
>> Btw, why we are mentioning 20 / 6 and 28 / 6 when arithmetically
>> it's the same as 10 / 3 and 14 / 3?
>
> I copied the BYT values from Thomas' email and I guess he did not
> get around to simplifying them, I'll use the simplified versions
> for my patch.

Too tired, too lazy :)

Andy, can you please make sure that people inside Intel who can look
into the secrit documentation confirm what we are aiming for?

Ideally they should provide the X-tal frequency and the mult/div pair
themself :)

Thanks,

        tglx