arch/x86: zefi must disable HPET before OS handoff
The firmware on existing devices uses HPET timer zero for its own
purposes, and leaves it alive with interrupts enabled. The Zephyr
driver now knows how to recover from this state with fuller
initialization, but that's not enough to fix the inherent race:
The timer can fire BEFORE the driver initialization happens (and does,
with certain versions of the EFI shell), thus flagging an interrupt to
what Zephyr sees as a garbage vector. The OS can't fix this on its
own, the EFI bootloader (which is running with interrupts enabled as
part of the EFI environment) has to do it. Here we can know that our
setting got there in time and didn't result in a stale interrupt flag
in the APIC waiting to blow up when interrupts get enabled.
Note: this is really just a workaround. It assumes the hardware has
an HPET with a standard address. Ideally we'd be able to build zefi
using Zephyr kconfig and devicetree values and predicate the HPET
reset on the correct configuraiton.
Signed-off-by: Andy Ross <andrew.j.ross@intel.com>
1 file changed
