On Fri 2015-08-21 19:53:34, Chen Yu wrote:

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 introducing a framework
for saving/restoring specify MSR registers(THERM_CONTROL in this case)
on suspend/resume.

When user finds a problematic platform that requires save/restore MSRs,
he can simply add quirk in msr_save_dmi_table, and customizes MSR
registers in quirk callback, for example:

unsigned int msr_id_need_to_save[] = {MSR_ID0, MSR_ID1, MSR_ID2...};

and system ensures that, once resumed from suspend, these MSR indicated
by IDs will be restored to their original values before suspend.

Since both 64/32-bit kernels are affected, this patch covers 64/32-bit
common code path. And because the MSR ids specified by user might not be
available or readable in any situation, we use rdmsrl_safe to safely
save these MSR registers.

Tested-by: Marcin Kaszewski <redacted>
Signed-off-by: Chen Yu <yu.c.chen@intel.com>

Acked-by: Pavel Machek <redacted>

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