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Date:   Mon, 18 Dec 2017 21:28:22 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Zhang Rui <rui.zhang@...el.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>, linux-x86 <x86@...nel.org>,
        Len Brown <len.brown@...el.com>,
        "Chen, Yu C" <yu.c.chen@...el.com>
Subject: Re: Regression: unable to boot after commit bd9240a18edf ("x86/apic:
 Add TSC_DEADLINE quirk due to errata") - Surface Pro 4 SKL


Hi, can you see if this makes you Surface boot?

I tested it on my IVB by making has_legacy_pic() return unconditional
true.

[    0.024000] tsc: Unable to calibrate against PIT
[    0.025000] tsc: using HPET reference calibration
[    0.026000] tsc: Detected 2792.451 MHz processor

---


diff --git a/arch/x86/include/asm/i8259.h b/arch/x86/include/asm/i8259.h
index c8376b40e882..e2cfc4b52ee4 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 8ea117f8142e..2afc623b2280 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 +364,15 @@ static unsigned long pit_calibrate_tsc(u32 latch, unsigned long ms, int loopmin)
 	unsigned long tscmin, tscmax;
 	int pitcnt;
 
+	if (!has_legacy_pic()) {
+		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 +497,9 @@ 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);
 

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