x86/tsc: Allow TSC calibration without PIT

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[ Upstream commit 30c7e5b123 ]

Zhang Rui reported that a Surface Pro 4 will fail to boot with
lapic=notscdeadline. Part of the problem is that that machine doesn't have
a PIT.

If, for some reason, the TSC init has to fall back to TSC calibration, it
relies on the PIT to be present.

Allow TSC calibration to reliably fall back to HPET.

The below results in an accurate TSC measurement when forced on a IVB:

  tsc: Unable to calibrate against PIT
  tsc: No reference (HPET/PMTIMER) available
  tsc: Unable to calibrate against PIT
  tsc: using HPET reference calibration
  tsc: Detected 2792.451 MHz processor

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: len.brown@intel.com
Cc: rui.zhang@intel.com
Link: https://lkml.kernel.org/r/20171222092243.333145937@infradead.org
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

...

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Peter Zijlstra 2017-12-22 10:20:11 +01:00 • committed by Greg Kroah-Hartman

parent 4a5d70332d

commit 239c948e32

2 changed files with 23 additions and 0 deletions

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5

arch/x86/include/asm/i8259.h

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18

arch/x86/kernel/tsc.c

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