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Replace the static initialization of the legacy clockevent with runtime initialization utilizing the common init function as the last preparatory step to switch the legacy clockevent over to the channel 0 storage in hpet_base. This comes with a twist. The static clockevent initializer has selected support for periodic and oneshot mode unconditionally whether the HPET config advertised periodic mode or not. Even the pre clockevents code did this. But.... Using the conditional in hpet_init_clockevent() makes at least Qemu and one hardware machine fail to boot. There are two issues which cause the boot failure: #1 After the timer delivery test in IOAPIC and the IOAPIC setup the next interrupt is not delivered despite the HPET channel being programmed correctly. Reprogramming the HPET after switching to IOAPIC makes it work again. After fixing this, the next issue surfaces: #2 Due to the unconditional periodic mode 'availability' the Local APIC timer calibration can hijack the global clockevents event handler without causing damage. Using oneshot at this stage makes if hang because the HPET does not get reprogrammed due to the handler hijacking. Duh, stupid me! Both issues require major surgery and especially the kick HPET again after enabling IOAPIC results in really nasty hackery. This 'assume periodic works' magic has survived since HPET support got added, so it's questionable whether this should be fixed. Both Qemu and the failing hardware machine support periodic mode despite the fact that both don't advertise it in the configuration register and both need that extra kick after switching to IOAPIC. Seems to be a feature... Keep the 'assume periodic works' magic around and add a big fat comment. Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Reviewed-by: Ingo Molnar <mingo@kernel.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Ricardo Neri <ricardo.neri-calderon@linux.intel.com> Cc: Ashok Raj <ashok.raj@intel.com> Cc: Andi Kleen <andi.kleen@intel.com> Cc: Suravee Suthikulpanit <Suravee.Suthikulpanit@amd.com> Cc: Stephane Eranian <eranian@google.com> Cc: Ravi Shankar <ravi.v.shankar@intel.com> Link: https://lkml.kernel.org/r/20190623132436.646565913@linutronix.de
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.