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acpi_timer: use ACPI-Fast if WAET timer one read flag is set 

The Windows ACPI Emulated Devices Table (WAET) has a hint to inform the OS
that a single read of the PM timer is reliable. Honour this flag.
This commit is contained in:
jmcneill 2021-07-25 01:43:08 +00:00
parent f83944e0d2
commit c211f59c20
1 changed files with 15 additions and 2 deletions
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17
sys/dev/acpi/acpi_timer.c
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@ -1,4 +1,4 @@
/* $NetBSD: acpi_timer.c,v 1.26 2020/05/29 12:30:41 rin Exp $ */
/* $NetBSD: acpi_timer.c,v 1.27 2021/07/25 01:43:08 jmcneill Exp $ */
/*-
* Copyright (c) 2006 Matthias Drochner <drochner@NetBSD.org>
@ -27,7 +27,7 @@
*/
#include <sys/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: acpi_timer.c,v 1.26 2020/05/29 12:30:41 rin Exp $");
__KERNEL_RCSID(0, "$NetBSD: acpi_timer.c,v 1.27 2021/07/25 01:43:08 jmcneill Exp $");
#include <sys/types.h>
#include <sys/systm.h>
@ -61,6 +61,7 @@ int
acpitimer_init(struct acpi_softc *sc)
{
#if (!ACPI_REDUCED_HARDWARE)
ACPI_TABLE_WAET *waet;
ACPI_STATUS rv;
uint32_t bits;
int i, j;
@ -79,6 +80,18 @@ acpitimer_init(struct acpi_softc *sc)
for (i = j = 0; i < 10; i++)
j += acpitimer_test();
rv = AcpiGetTable(ACPI_SIG_WAET, 0, (ACPI_TABLE_HEADER **)&waet);
if (ACPI_SUCCESS(rv)) {
/*
* Windows ACPI Emulated Devices Table (WAET) has a hint
* to let the OS know that a single read of the PM timer
* provides a reliable value.
*/
if ((waet->Flags & ACPI_WAET_TIMER_ONE_READ) != 0) {
j += 10;
}
}
if (j >= 10) {
acpi_timecounter.tc_name = "ACPI-Fast";
acpi_timecounter.tc_get_timecount = acpitimer_read_fast;