From 239c948e3266adba944da4ea257362e773f39823 Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Fri, 22 Dec 2017 10:20:11 +0100 Subject: [PATCH] x86/tsc: Allow TSC calibration without PIT [ Upstream commit 30c7e5b123673d5e570e238dbada2fb68a87212c ] 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) Signed-off-by: Thomas Gleixner 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 Signed-off-by: Greg Kroah-Hartman --- arch/x86/include/asm/i8259.h | 5 +++++ arch/x86/kernel/tsc.c | 18 ++++++++++++++++++ 2 files changed, 23 insertions(+) diff --git a/arch/x86/include/asm/i8259.h b/arch/x86/include/asm/i8259.h index c8376b40e882..5cdcdbd4d892 100644 --- a/arch/x86/include/asm/i8259.h +++ b/arch/x86/include/asm/i8259.h @@ -69,6 +69,11 @@ struct legacy_pic { extern struct legacy_pic *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) { return legacy_pic->nr_legacy_irqs; diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c index 183a3a142309..0bf06fa3027e 100644 --- a/arch/x86/kernel/tsc.c +++ b/arch/x86/kernel/tsc.c @@ -25,6 +25,7 @@ #include #include #include +#include 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); -- 2.20.1