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| author | Felix Held <felix-coreboot@felixheld.de> | 2023-03-24 22:07:48 +0100 |
|---|---|---|
| committer | Felix Held <felix-coreboot@felixheld.de> | 2023-03-29 13:24:17 +0000 |
| commit | c08d804f01d88ac028c7271f0efed07373c3bc97 (patch) | |
| tree | 0eabe66f9ddee3089803ebf30bf81a2ed463067a /src/soc/amd | |
| parent | 77c5d898aecbb15b37e4458cd32ca95f10e2264e (diff) | |
soc/amd/stoneyridge/monotonic_time: add comment that we can't use TSC
Due to a non-constant TSC rate before the microcode update is applied,
the Performance Time Stamp Counter is used instead. To clarify this, add
a comment to the timestamp_get implementation. See commit 24079323d4d8
("soc/amd/stoneyridge: provide alternate monotonic timer") and the
description of the TscInvariant bit in CPUID Fn8000_0007_EDX Advanced
Power Management Information in the public version of BKDG #55072 Rev
3.09 for more details.
Signed-off-by: Felix Held <felix-coreboot@felixheld.de>
Change-Id: I824b372c36fa6f3eb912469b235a9474f6a58ff5
Reviewed-on: https://review.coreboot.org/c/coreboot/+/74018
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Eric Lai <eric_lai@quanta.corp-partner.google.com>
Diffstat (limited to 'src/soc/amd')
| -rw-r--r-- | src/soc/amd/stoneyridge/monotonic_timer.c | 2 |
1 files changed, 2 insertions, 0 deletions
diff --git a/src/soc/amd/stoneyridge/monotonic_timer.c b/src/soc/amd/stoneyridge/monotonic_timer.c index 06e0c93413..bd1e4e7aac 100644 --- a/src/soc/amd/stoneyridge/monotonic_timer.c +++ b/src/soc/amd/stoneyridge/monotonic_timer.c @@ -12,6 +12,8 @@ void timer_monotonic_get(struct mono_time *mt) mono_time_set_usecs(mt, timestamp_get()); } +/* The TSC has a non-constant rate before the microcode update is applied, so it can't be used + in timestamp_get before that. Instead, the Performance Time Stamp Counter is used. */ uint64_t timestamp_get(void) { msr_t msr; |