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| author | Peter Zijlstra <peterz@infradead.org> | 2017-12-22 12:20:11 +0300 |
|---|---|---|
| committer | Thomas Gleixner <tglx@linutronix.de> | 2018-01-14 22:18:23 +0300 |
| commit | 30c7e5b123673d5e570e238dbada2fb68a87212c (patch) | |
| tree | 2b1ccd53e66e21b0f5f8a6f0afc3a3bf19975513 /arch/x86/kernel/tsc.c | |
| parent | 4b5b2127238e689ee18aa6752959751dd61c4c73 (diff) | |
| download | linux-30c7e5b123673d5e570e238dbada2fb68a87212c.tar.xz | |
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: 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
Diffstat (limited to 'arch/x86/kernel/tsc.c')
| -rw-r--r-- | arch/x86/kernel/tsc.c | 18 |
1 files changed, 18 insertions, 0 deletions
diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c index e169e85db434..a2c9dd8bfc6f 100644 --- a/arch/x86/kernel/tsc.c +++ b/arch/x86/kernel/tsc.c @@ -25,6 +25,7 @@ #include <asm/geode.h> #include <asm/apic.h> #include <asm/intel-family.h> +#include <asm/i8259.h> unsigned int __read_mostly cpu_khz; /* TSC clocks / usec, not used here */ 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; 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 */ outb((inb(0x61) & ~0x02) | 0x01, 0x61); @@ -487,6 +502,9 @@ static unsigned long quick_pit_calibrate(void) u64 tsc, delta; unsigned long d1, d2; + if (!has_legacy_pic()) + return 0; + /* Set the Gate high, disable speaker */ outb((inb(0x61) & ~0x02) | 0x01, 0x61); |