[src/trunk]: src/sys/arch/alpha/alpha Provide an alternate delay function tha...

[thorpej <thorpej%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/53c58dfe0915
branches:  trunk
changeset: 940092:53c58dfe0915
user:      thorpej <thorpej%NetBSD.org@localhost>
date:      Sat Oct 03 17:32:49 2020 +0000

description:
Provide an alternate delay function that uses the Qemu get-time hypercall.

diffstat:

 sys/arch/alpha/alpha/qemu.c |  53 +++++++++++++++++++++++++++++++++++++++-----
 1 files changed, 46 insertions(+), 7 deletions(-)

diffs (95 lines):

diff -r 9817b17b8808 -r 53c58dfe0915 sys/arch/alpha/alpha/qemu.c
--- a/sys/arch/alpha/alpha/qemu.c       Sat Oct 03 17:31:46 2020 +0000
+++ b/sys/arch/alpha/alpha/qemu.c       Sat Oct 03 17:32:49 2020 +0000
@@ -1,4 +1,4 @@
-/* $NetBSD: qemu.c,v 1.2 2020/09/29 01:33:00 thorpej Exp $ */
+/* $NetBSD: qemu.c,v 1.3 2020/10/03 17:32:49 thorpej Exp $ */
 
 /*-
  * Copyright (c) 2020 The NetBSD Foundation, Inc.
@@ -56,8 +56,10 @@
        struct timecounter sc_tc;
 };
 
-static u_int
-qemu_get_timecount(struct timecounter * const tc __unused)
+static unsigned long qemu_nsec_per_tick __read_mostly = (unsigned long)-1;
+
+static inline unsigned long
+qemu_get_vmtime(void)
 {
        register unsigned long v0 __asm("$0");
        register unsigned long a0 __asm("$16") = 7;     /* Qemu get-time */
@@ -67,7 +69,41 @@
                : "i"(PAL_cserve)
                : "$17", "$18", "$19", "$20", "$21");
 
-       return (u_int)v0;
+       return v0;
+}
+
+static void
+qemu_delay(unsigned long usec)
+{
+       /* Get starting point. */
+       const unsigned long base = qemu_get_vmtime();
+
+       /* convert request from usec to nsec */
+       const unsigned long nsec = usec * 1000;
+       KASSERT(nsec > usec);
+
+       /* Figure out finish line. */
+       const unsigned long finished = base + nsec;
+       KASSERT(finished > base);
+
+       unsigned long now;
+
+       /* Spin until we're finished. */
+       while ((now = qemu_get_vmtime()) < finished) {
+               /*
+                * If we have more than one clock tick worth of spinning
+                * to do, when use WTINT to wait at a low power state.
+                */
+               if (finished - now > qemu_nsec_per_tick) {
+                       alpha_pal_wtint(0);
+               }
+       }
+}
+
+static u_int
+qemu_get_timecount(struct timecounter * const tc __unused)
+{
+       return (u_int)qemu_get_vmtime();
 }
 
 static inline void
@@ -82,8 +118,6 @@
                : "$0", "$18", "$19", "$20", "$21");
 }
 
-static unsigned long qemu_nsec_per_tick __read_mostly;
-
 static void
 qemu_hardclock(struct clockframe * const framep)
 {
@@ -102,7 +136,7 @@
 qemu_clock_init(void * const v __unused)
 {
        /* First-time initialization... */
-       if (qemu_nsec_per_tick == 0) {
+       if (qemu_nsec_per_tick == (unsigned long)-1) {
                KASSERT(CPU_IS_PRIMARY(curcpu()));
                qemu_nsec_per_tick = 1000000000UL / hz;
 
@@ -175,6 +209,11 @@
         * Qemu's PALcode implements WTINT; use it to save host cycles.
         */
        cpu_idle_fn = cpu_idle_wtint;
+
+       /*
+        * Use Qemu's "VM time" hypercall to implement delay().
+        */
+       alpha_delay_fn = qemu_delay;
 }
 
 CFATTACH_DECL_NEW(qemu, sizeof(struct qemu_softc),