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soc/intel/pmc: add a note about legacy OSes/payloads to PM Timer Kconfig

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Since ACPI 5.0A it is allowed to disable the ACPI Timer, when the
according FADT flag `ACPI_FADT_PLATFORM_CLOCK` is unset.

Starting with Skylake, most platforms (except Xeon-SP) support PM Timer
emulation, so even legacy OSes and payloads should work fine with the
hardware PM Timer disabled. However, when the `TMR_STS` functionality
is required, some legacy OSes might still not work (properly).

Add a note about this to the Kconfig help.

Change-Id: I53f1814113902124779ed85da030374439570688
Signed-off-by: Michael Niewöhner <foss@mniewoehner.de>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/58018
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Nico Huber <nico.h@gmx.de>
Reviewed-by: Lance Zhao
This commit is contained in:
Michael Niewöhner 2021-09-25 00:10:30 +02:00 committed by Nico Huber
parent 5c259642c2
commit c47fc40022
1 changed files with 7 additions and 0 deletions
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7
src/soc/intel/common/block/pmc/Kconfig
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@ -76,4 +76,11 @@ config USE_PM_ACPI_TIMER
Disabling this option also stops the hardware TCO timer and makes Disabling this option also stops the hardware TCO timer and makes
the TCO watchdog unavailable. the TCO watchdog unavailable.
Note: On platforms without uCode PM Timer emulation, legacy OSes
or payloads with ACPI version < 5.0A might not work without
PM ACPI timer.
(Legacy) software requiring `TMR_STS` (for timer overflow
interrupts) will not work with this option disabled.
endif # PM_ACPI_TIMER_OPTIONAL endif # PM_ACPI_TIMER_OPTIONAL