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    SubjectRe: setup_boot_APIC_clock() NULL dereference during early boot on reduced hardware platforms
    On Thu, Aug 1, 2019 at 2:26 PM Daniel Drake <drake@endlessm.com> wrote:
    >
    > Hi,
    >
    > Working with a new consumer laptop based on AMD R7-3700U, we are
    > seeing a kernel panic during early boot (before the display
    > initializes). It's a new product and there is no previous known
    > working kernel version (tested 5.0, 5.2 and current linus master).
    >
    > We may have also seen this problem on a MiniPC based on AMD APU 7010
    > from another vendor, but we don't have it in hands right now to
    > confirm that it's the exact same crash.
    >
    > earlycon shows the details: a NULL dereference under
    > setup_boot_APIC_clock(), which actually happens in
    > calibrate_APIC_clock():
    >
    > /* Replace the global interrupt handler */
    > real_handler = global_clock_event->event_handler;
    > global_clock_event->event_handler = lapic_cal_handler;
    >
    > 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
    clock source on your platform, like HPET?

    Thanks,
    -Aubrey

    > However I'm probably missing part of the big picture here, as this
    > only makes boot fail later on. It continues til the next point that
    > something leads to schedule(), such as a driver calling msleep() or
    > mark_readonly() calling rcu_barrier(), etc. Then it hangs.
    >
    > Is something missing in terms of timer setup here? Suggestions appreciated...
    >
    > Thanks
    > Daniel

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