[PATCH] x86, suspend: Save/restore THERM_CONTROL register for suspend

[Chen Yu <yu.c.chen@intel.com>]

A bug is reported(https://bugzilla.redhat.com/show_bug.cgi?id=1227208)
that, after resuming from S3, CPU is working at a low speed.
After investigation, it is found that, BIOS has modified the value
of THERM_CONTROL register during S3, changes it from 0 to 0x10,
while the latter means CPU can only get 25% of the Duty Cycle,
and this caused the problem.

Simple scenario to reproduce:
1.Boot up system
2.Get MSR with address 0x19a, it should output 0
3.Put system into sleep, then wake up
4.Get MSR with address 0x19a, it should output 0(actual it outputs 0x10)

Although this is a BIOS issue, it would be more robust for linux to deal
with this situation. This patch fixes this issue by saving/restoring
THERM_CONTROL(now called CLOCK_MODULATION) register on suspend/resume.

Tested-by: Marcin Kaszewski <marcin.kaszewski@intel.com>
Signed-off-by: Chen Yu <yu.c.chen@intel.com>
---
 arch/x86/include/asm/suspend_64.h | 1 +
 arch/x86/power/cpu.c              | 2 ++
 2 files changed, 3 insertions(+)

diff --git a/arch/x86/include/asm/suspend_64.h b/arch/x86/include/asm/suspend_64.h
index 7ebf0eb..b9f5591 100644
--- a/arch/x86/include/asm/suspend_64.h
+++ b/arch/x86/include/asm/suspend_64.h
@@ -25,6 +25,7 @@ struct saved_context {
 	u64 misc_enable;
 	bool misc_enable_saved;
 	unsigned long efer;
+	unsigned long clock_modulation;
 	u16 gdt_pad; /* Unused */
 	struct desc_ptr gdt_desc;
 	u16 idt_pad;
diff --git a/arch/x86/power/cpu.c b/arch/x86/power/cpu.c
index 9ab5279..f82577b 100644
--- a/arch/x86/power/cpu.c
+++ b/arch/x86/power/cpu.c
@@ -97,6 +97,7 @@ static void __save_processor_state(struct saved_context *ctxt)
 	mtrr_save_fixed_ranges(NULL);
 
 	rdmsrl(MSR_EFER, ctxt->efer);
+	rdmsrl(MSR_IA32_THERM_CONTROL, ctxt->clock_modulation);
 #endif
 
 	/*
@@ -178,6 +179,7 @@ static void notrace __restore_processor_state(struct saved_context *ctxt)
 #else
 /* CONFIG X86_64 */
 	wrmsrl(MSR_EFER, ctxt->efer);
+	wrmsrl(MSR_IA32_THERM_CONTROL, ctxt->clock_modulation);
 	write_cr8(ctxt->cr8);
 	__write_cr4(ctxt->cr4);
 #endif
-- 
1.8.4.2