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Date:   Thu, 1 Aug 2019 12:17:33 +0200 (CEST)
From:   Thomas Gleixner <tglx@linutronix.de>
To:     Daniel Drake <drake@endlessm.com>
cc:     Aubrey Li <aubrey.intel@gmail.com>, x86@kernel.org,
        "Li, Aubrey" <aubrey.li@linux.intel.com>,
        Ingo Molnar <mingo@redhat.com>,
        "H . Peter Anvin" <hpa@zytor.com>,
        Linux Kernel <linux-kernel@vger.kernel.org>,
        Endless Linux Upstreaming Team <linux@endlessm.com>
Subject: Re: setup_boot_APIC_clock() NULL dereference during early boot on
 reduced hardware platforms
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On Thu, 1 Aug 2019, Daniel Drake wrote:
> On Thu, Aug 1, 2019 at 3:16 PM Aubrey Li <aubrey.intel@gmail.com> wrote:
> However, the only way this can be called is from hpet_enable().
> 
> hpet_enable() is called from 2 places:
>  1. From hpet_time_init(). This is the default x86 timer_init that
> acpi_generic_reduced_hw_init() took out of action here.
>  2. From hpet_late_init(). However that function is only called late,
> after calibrate_APIC_clock() has already crashed the kernel. Also,
> even if moved earlier it would also not call hpet_enable() here
> because the ACPI HPET table parsing has already populated
> hpet_address.
> 
> I tried slotting in a call to hpet_enable() at an earlier point
> regardless, but I still end up with the kernel hanging later during
> boot, probably because irq0 fails to be setup and this error is hit:
>     if (setup_irq(0, &irq0))
>         pr_info("Failed to register legacy timer interrupt\n");

Right. The thing also lacks PIT :)

So there are two options:

   1) Make sure the HPET is parsed somehow even with the reduced stuff

   2) Make the clock frequency detection work.

#1 is a trainwreck

#2 is something we really want to have anyway. See the other reply. I cc'ed
   Tom there, he should be able to give us the missing link.

Thanks,

	tglx