Commit 30c7e5b1 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Thomas Gleixner
Browse files

x86/tsc: Allow TSC calibration without PIT 



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: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Cc: len.brown@intel.com
Cc: rui.zhang@intel.com
Link: https://lkml.kernel.org/r/20171222092243.333145937@infradead.org
parent 4b5b2127

arch/x86/include/asm/i8259.h

+5 −0
Original line number Original line Diff line number Diff line
@@ -69,6 +69,11 @@ struct legacy_pic { 
extern struct legacy_pic *legacy_pic;

extern struct legacy_pic *legacy_pic;

extern struct legacy_pic null_legacy_pic;

extern struct legacy_pic null_legacy_pic;





static inline bool has_legacy_pic(void)

{

	return legacy_pic != &null_legacy_pic;

}



static inline int nr_legacy_irqs(void)

static inline int nr_legacy_irqs(void)

{

{

	return legacy_pic->nr_legacy_irqs;

	return legacy_pic->nr_legacy_irqs;

arch/x86/kernel/tsc.c

+18 −0
Original line number Original line Diff line number Diff line
@@ -25,6 +25,7 @@ 
#include <asm/geode.h>

#include <asm/geode.h>

#include <asm/apic.h>

#include <asm/apic.h>

#include <asm/intel-family.h>

#include <asm/intel-family.h>

#include <asm/i8259.h>





unsigned int __read_mostly cpu_khz;	/* TSC clocks / usec, not used here */

unsigned int __read_mostly cpu_khz;	/* TSC clocks / usec, not used here */

EXPORT_SYMBOL(cpu_khz);

EXPORT_SYMBOL(cpu_khz);
@@ -363,6 +364,20 @@ static unsigned long pit_calibrate_tsc(u32 latch, unsigned long ms, int loopmin) 
	unsigned long tscmin, tscmax;

	unsigned long tscmin, tscmax;

	int pitcnt;

	int pitcnt;





	if (!has_legacy_pic()) {

		/*

		 * Relies on tsc_early_delay_calibrate() to have given us semi

		 * usable udelay(), wait for the same 50ms we would have with

		 * the PIT loop below.

		 */

		udelay(10 * USEC_PER_MSEC);

		udelay(10 * USEC_PER_MSEC);

		udelay(10 * USEC_PER_MSEC);

		udelay(10 * USEC_PER_MSEC);

		udelay(10 * USEC_PER_MSEC);

		return ULONG_MAX;

	}



	/* Set the Gate high, disable speaker */

	/* Set the Gate high, disable speaker */

	outb((inb(0x61) & ~0x02) | 0x01, 0x61);

	outb((inb(0x61) & ~0x02) | 0x01, 0x61);
@@ -487,6 +502,9 @@ static unsigned long quick_pit_calibrate(void) 
	u64 tsc, delta;

	u64 tsc, delta;

	unsigned long d1, d2;

	unsigned long d1, d2;





	if (!has_legacy_pic())

		return 0;



	/* Set the Gate high, disable speaker */

	/* Set the Gate high, disable speaker */

	outb((inb(0x61) & ~0x02) | 0x01, 0x61);

	outb((inb(0x61) & ~0x02) | 0x01, 0x61);

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