linux-kernel - [v1 7/9] x86/tsc: use cpuid to determine CPU frequency

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Date:   Wed, 22 Mar 2017 16:24:23 -0400
From:   Pavel Tatashin <pasha.tatashin@...cle.com>
To:     x86@...nel.org, linux-kernel@...r.kernel.org, mingo@...hat.com,
        peterz@...radead.org, tglx@...utronix.de, hpa@...or.com
Subject: [v1 7/9] x86/tsc: use cpuid to determine CPU frequency

Newer processors implement cpuid extension to determine CPU frequency
from cpuid. This patch adds a function that can do this early in boot.

Signed-off-by: Pavel Tatashin <pasha.tatashin@...cle.com>
---
 arch/x86/kernel/tsc.c |   10 ++++++----
 1 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index 1c9fc23..58bd575 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -743,14 +743,14 @@ unsigned long native_calibrate_tsc(void)
 	return tsc_khz;
 }
 
-static unsigned long cpu_khz_from_cpuid(void)
+static unsigned long cpu_khz_from_cpuid_early(int vendor, int cpuid_level)
 {
 	unsigned int eax_base_mhz, ebx_max_mhz, ecx_bus_mhz, edx;
 
-	if (boot_cpu_data.x86_vendor != X86_VENDOR_INTEL)
+	if (vendor != X86_VENDOR_INTEL)
 		return 0;
 
-	if (boot_cpu_data.cpuid_level < 0x16)
+	if (cpuid_level < 0x16)
 		return 0;
 
 	eax_base_mhz = ebx_max_mhz = ecx_bus_mhz = edx = 0;
@@ -770,7 +770,9 @@ unsigned long native_calibrate_cpu(void)
 	unsigned long flags, latch, ms, fast_calibrate;
 	int hpet = is_hpet_enabled(), i, loopmin;
 
-	fast_calibrate = cpu_khz_from_cpuid();
+	fast_calibrate = cpu_khz_from_cpuid_early(boot_cpu_data.x86_vendor,
+						  boot_cpu_data.cpuid_level);
+
 	if (fast_calibrate)
 		return fast_calibrate;
 
-- 
1.7.1