acpitimer(4): add acpitimer_delay(), another delay(9) implementation

When lapic_delay() is removed from the tree in the near future, older
machines without a constant/invariant TSC will need a delay(9)
implementation better than i8254_delay().

This patch adds acpitimer_delay(), a delay(9) implementation based on
the ACPI PM timer.  It is only preferable to i8254_delay(), so set its
quality to 1000.

With input from jsg@.

Link: https://marc.info/?l=openbsd-tech&m=166053729104923&w=2
ok mlarkin@ jsg@

diff --git a/sys/dev/acpi/acpitimer.c b/sys/dev/acpi/acpitimer.c
index 7b04127..570402f 100644 (file)
--- a/sys/dev/acpi/acpitimer.c
+++ b/sys/dev/acpi/acpitimer.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: acpitimer.c,v 1.15 2022/04/06 18:59:27 naddy Exp $ */
+/* $OpenBSD: acpitimer.c,v 1.16 2022/08/25 17:43:34 cheloha Exp $ */
 /*
  * Copyright (c) 2005 Thorsten Lockert <tholo@sigmasoft.com>
  *
@@ -18,17 +18,27 @@
 #include <sys/param.h>
 #include <sys/systm.h>
 #include <sys/device.h>
+#include <sys/stdint.h>
 #include <sys/timetc.h>
 
 #include <machine/bus.h>
+#include <machine/cpu.h>
 
 #include <dev/acpi/acpireg.h>
 #include <dev/acpi/acpivar.h>
 
+struct acpitimer_softc {
+       struct device           sc_dev;
+
+       bus_space_tag_t         sc_iot;
+       bus_space_handle_t      sc_ioh;
+};
+
 int acpitimermatch(struct device *, void *, void *);
 void acpitimerattach(struct device *, struct device *, void *);
-
+void acpitimer_delay(int);
 u_int acpi_get_timecount(struct timecounter *tc);
+uint32_t acpitimer_read(struct acpitimer_softc *);
 
 static struct timecounter acpi_timecounter = {
        .tc_get_timecount = acpi_get_timecount,
@@ -41,13 +51,6 @@ static struct timecounter acpi_timecounter = {
        .tc_user = 0,
 };
 
-struct acpitimer_softc {
-       struct device           sc_dev;
-
-       bus_space_tag_t         sc_iot;
-       bus_space_handle_t      sc_ioh;
-};
-
 const struct cfattach acpitimer_ca = {
        sizeof(struct acpitimer_softc), acpitimermatch, acpitimerattach
 };
@@ -98,18 +101,43 @@ acpitimerattach(struct device *parent, struct device *self, void *aux)
        acpi_timecounter.tc_priv = sc;
        acpi_timecounter.tc_name = sc->sc_dev.dv_xname;
        tc_init(&acpi_timecounter);
+
+       delay_init(acpitimer_delay, 1000);
+
 #if defined(__amd64__)
        extern void cpu_recalibrate_tsc(struct timecounter *);
        cpu_recalibrate_tsc(&acpi_timecounter);
 #endif
 }
 
+void
+acpitimer_delay(int usecs)
+{
+       uint64_t count = 0, cycles;
+       struct acpitimer_softc *sc = acpi_timecounter.tc_priv;
+       uint32_t mask = acpi_timecounter.tc_counter_mask;
+       uint32_t val1, val2;
+
+       val2 = acpitimer_read(sc);
+       cycles = usecs * acpi_timecounter.tc_frequency / 1000000;
+       while (count < cycles) {
+               CPU_BUSY_CYCLE();
+               val1 = val2;
+               val2 = acpitimer_read(sc);
+               count += (val2 - val1) & mask;
+       }
+}
 
 u_int
 acpi_get_timecount(struct timecounter *tc)
 {
-       struct acpitimer_softc *sc = tc->tc_priv;
-       u_int u1, u2, u3;
+       return acpitimer_read(tc->tc_priv);
+}
+
+uint32_t
+acpitimer_read(struct acpitimer_softc *sc)
+{
+       uint32_t u1, u2, u3;
 
        u2 = bus_space_read_4(sc->sc_iot, sc->sc_ioh, 0);
        u3 = bus_space_read_4(sc->sc_iot, sc->sc_ioh, 0);