linux-kernel - Re: setup_boot_APIC_clock() NULL dereference during early boot on reduced hardware platforms

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Date:   Thu, 1 Aug 2019 15:44:19 +0000
From:   "Lendacky, Thomas" <Thomas.Lendacky@....com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        "Li, Aubrey" <aubrey.li@...ux.intel.com>
CC:     Aubrey Li <aubrey.intel@...il.com>,
        Daniel Drake <drake@...lessm.com>,
        "x86@...nel.org" <x86@...nel.org>, Ingo Molnar <mingo@...hat.com>,
        "H . Peter Anvin" <hpa@...or.com>,
        Linux Kernel <linux-kernel@...r.kernel.org>,
        Endless Linux Upstreaming Team <linux@...lessm.com>
Subject: Re: setup_boot_APIC_clock() NULL dereference during early boot on
 reduced hardware platforms

On 8/1/19 5:13 AM, Thomas Gleixner wrote:
> On Thu, 1 Aug 2019, Li, Aubrey wrote:
>> On 2019/8/1 16:13, Thomas Gleixner wrote:
>>> The point is that it does not matter which vendor a CPU comes from. The
>>> kernel does support legacyless boot when the frequencies are known. Whether
>>> that's currently possible on that particular CPU is a different question.
>>>
>> Yeah, I should specify, Daniel, your platform needs a global clock event, ;-)
> 
> Care to look at the manuals before making assumptions?
> 
>   2.1.9 Timers
> 
>    Each core includes the following timers. These timers do not vary in
>    frequency regardless of the current P-state or C-state.
> 
>    * Core::X86::Msr::TSC; the TSC increments at the rate specified by the
>      P0 Pstate. See Core::X86::Msr::PStateDef.
> 
>    * The APIC timer (Core::X86::Apic::TimerInitialCount and
>      Core::X86::Apic::TimerCurrentCount), which increments at the rate of
>      2xCLKIN; the APIC timer may increment in units of between 1 and 8.
> 
> The Ryzens use a 100MHz input clock for the APIC normally, but I'm not sure
> whether this is subject to overclocking. If so then it should be possible
> to figure that out somehow. Tom?

Let me check with the hardware folks and I'll get back to you.

Thanks,
Tom

> 
> Thanks,
> 
> 	tglx
>