Module Name: src
Committed By: ad
Date: Fri Apr 24 22:25:07 UTC 2020
Modified Files:
src/sys/dev/ic: hpet.c
Log Message:
On attach figure out how long a single read of the counter register takes
and use that for the adjustment in hpet_delay().
To generate a diff of this commit:
cvs rdiff -u -r1.14 -r1.15 src/sys/dev/ic/hpet.c
Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.
Modified files:
Index: src/sys/dev/ic/hpet.c
diff -u src/sys/dev/ic/hpet.c:1.14 src/sys/dev/ic/hpet.c:1.15
--- src/sys/dev/ic/hpet.c:1.14 Thu Apr 23 20:33:57 2020
+++ src/sys/dev/ic/hpet.c Fri Apr 24 22:25:07 2020
@@ -1,4 +1,4 @@
-/* $NetBSD: hpet.c,v 1.14 2020/04/23 20:33:57 ad Exp $ */
+/* $NetBSD: hpet.c,v 1.15 2020/04/24 22:25:07 ad Exp $ */
/*
* Copyright (c) 2006 Nicolas Joly
@@ -33,7 +33,7 @@
*/
#include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: hpet.c,v 1.14 2020/04/23 20:33:57 ad Exp $");
+__KERNEL_RCSID(0, "$NetBSD: hpet.c,v 1.15 2020/04/24 22:25:07 ad Exp $");
#include <sys/systm.h>
#include <sys/device.h>
@@ -79,7 +79,7 @@ hpet_attach_subr(device_t dv)
struct hpet_softc *sc = device_private(dv);
struct timecounter *tc;
uint64_t tmp;
- uint32_t val;
+ uint32_t val, sval, eval;
int i;
tc = &sc->sc_tc;
@@ -130,6 +130,19 @@ hpet_attach_subr(device_t dv)
if (device_unit(dv) == 0)
hpet0 = sc;
+
+ /*
+ * Determine approximately how long it takes to read the counter
+ * register once, and compute an ajustment for hpet_delay() based on
+ * that.
+ */
+ (void)bus_space_read_4(sc->sc_memt, sc->sc_memh, HPET_MCOUNT_LO);
+ sval = bus_space_read_4(sc->sc_memt, sc->sc_memh, HPET_MCOUNT_LO);
+ for (i = 0; i < 998; i++)
+ (void)bus_space_read_4(sc->sc_memt, sc->sc_memh, HPET_MCOUNT_LO);
+ eval = bus_space_read_4(sc->sc_memt, sc->sc_memh, HPET_MCOUNT_LO);
+ val = eval - sval;
+ sc->sc_adj = (int64_t)val * sc->sc_period / 1000;
}
static u_int
@@ -168,13 +181,13 @@ hpet_delay(unsigned int us)
int64_t delta;
/*
- * Read timer before slow division. Assume that each read of the
- * HPET costs ~500ns. Aim for the middle and subtract 750ns for
- * overhead.
+ * Read timer before slow division. Convert microseconds to
+ * femtoseconds, subtract the cost of 1 counter register access,
+ * and convert to HPET units.
*/
sc = hpet0;
otick = bus_space_read_4(sc->sc_memt, sc->sc_memh, HPET_MCOUNT_LO);
- delta = (((int64_t)us * 1000000000) - 750000000) / sc->sc_period;
+ delta = (((int64_t)us * 1000000000) - sc->sc_adj) / sc->sc_period;
while (delta > 0) {
SPINLOCK_BACKOFF_HOOK;
