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Date:   Thu, 1 Aug 2019 09:35:33 +0200 (CEST)
From:   Thomas Gleixner <tglx@linutronix.de>
To:     Aubrey Li <aubrey.intel@gmail.com>
cc:     Daniel Drake <drake@endlessm.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, Aubrey Li wrote:
> On Thu, Aug 1, 2019 at 2:26 PM Daniel Drake <drake@endlessm.com> wrote:
> > global_clock_event is NULL here. This is a "reduced hardware" ACPI
> > platform so acpi_generic_reduced_hw_init() has set timer_init to NULL,
> > avoiding the usual codepaths that would set up global_clock_event.
> >
> IIRC, acpi_generic_reduced_hw_init() avoids initializing PIT, the status of
> this legacy device is unknown in ACPI hw-reduced mode.
> 
> > I tried the obvious:
> >  if (!global_clock_event)
> >     return -1;
> >
> No, the platform needs a global clock event, can you turn on some other

Wrong. The kernel boots perfectly fine without a global clock event. But
for that the TSC and LAPIC frequency must be known.

Thanks,

	tglx