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x86/tsc: Read all ratio bits from MSR_PLATFORM_INFO 

Currently we read the tsc radio: ratio = (MSR_PLATFORM_INFO >> 8) & 0x1f;

Thus we get bit 8-12 of MSR_PLATFORM_INFO, however according to the SDM
(35.5), the ratio bits are bit 8-15.

Ignoring the upper bits can result in an incorrect tsc ratio, which causes the
TSC calibration and the Local APIC timer frequency to be incorrect.

Fix this problem by masking 0xff instead.

[ tglx: Massaged changelog ]

Fixes: 7da7c15613 "x86, tsc: Add static (MSR) TSC calibration on Intel Atom SoCs"
Signed-off-by: Chen Yu <yu.c.chen@intel.com>
Cc: "Rafael J. Wysocki" <rafael@kernel.org>
Cc: stable@vger.kernel.org
Cc: Bin Gao <bin.gao@intel.com>
Cc: Len Brown <lenb@kernel.org>
Link: http://lkml.kernel.org/r/1462505619-5516-1-git-send-email-yu.c.chen@intel.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
This commit is contained in:
Chen Yu 2016-05-06 11:33:39 +08:00 committed by Thomas Gleixner
parent 08914f436b
commit 886123fb3a
1 changed files with 1 additions and 1 deletions
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2
arch/x86/kernel/tsc_msr.c
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@ -92,7 +92,7 @@ unsigned long try_msr_calibrate_tsc(void)
if (freq_desc_tables[cpu_index].msr_plat) {
rdmsr(MSR_PLATFORM_INFO, lo, hi);
ratio = (lo >> 8) & 0x1f;
ratio = (lo >> 8) & 0xff;
} else {
rdmsr(MSR_IA32_PERF_STATUS, lo, hi);
ratio = (hi >> 8) & 0x1f;