[src/trunk]: src/sys/arch/arm/cortex Sprinkle some arm_isb() to force executi...

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

details:   https://anonhg.NetBSD.org/src/rev/363902d3c31c
branches:  trunk
changeset: 336865:363902d3c31c
user:      matt <matt%NetBSD.org@localhost>
date:      Tue Mar 24 08:58:41 2015 +0000

description:
Sprinkle some arm_isb() to force execution of the mcrr instructions to get
more accurate values.  (Given that the generic timer is usually running at
a 64th or less of the cpu clock, this only settle to a tick or so.)

diffstat:

 sys/arch/arm/cortex/gtmr.c |  26 ++++++++++++++++++++------
 1 files changed, 20 insertions(+), 6 deletions(-)

diffs (96 lines):

diff -r 5336d45ce63a -r 363902d3c31c sys/arch/arm/cortex/gtmr.c
--- a/sys/arch/arm/cortex/gtmr.c        Tue Mar 24 08:38:29 2015 +0000
+++ b/sys/arch/arm/cortex/gtmr.c        Tue Mar 24 08:58:41 2015 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: gtmr.c,v 1.10 2015/03/23 23:33:22 jmcneill Exp $       */
+/*     $NetBSD: gtmr.c,v 1.11 2015/03/24 08:58:41 matt Exp $   */
 
 /*-
  * Copyright (c) 2012 The NetBSD Foundation, Inc.
@@ -30,7 +30,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: gtmr.c,v 1.10 2015/03/23 23:33:22 jmcneill Exp $");
+__KERNEL_RCSID(0, "$NetBSD: gtmr.c,v 1.11 2015/03/24 08:58:41 matt Exp $");
 
 #include <sys/param.h>
 #include <sys/bus.h>
@@ -44,6 +44,8 @@
 
 #include <prop/proplib.h>
 
+#include <arm/locore.h>
+
 #include <arm/cortex/gtmr_var.h>
 
 #include <arm/cortex/mpcore_var.h>
@@ -169,6 +171,7 @@
         * Get now and update the compare timer.
         */
        ci->ci_lastintr = armreg_cntv_ct_read();
+       arm_isb();
        armreg_cntv_tval_write(sc->sc_autoinc);
 #if 0
        printf("%s: %s: delta cval = %"PRIu64"\n",
@@ -186,14 +189,17 @@
 
        uint64_t now64;
        uint64_t start64 = armreg_cntv_ct_read();
+       arm_isb();
        do {
                now64 = armreg_cntv_ct_read();
+               arm_isb();
        } while (start64 == now64);
        start64 = now64;
        uint64_t end64 = start64 + 64;
        uint32_t start32 = armreg_pmccntr_read();
        do {
                now64 = armreg_cntv_ct_read();
+               arm_isb();
        } while (end64 != now64);
        uint32_t end32 = armreg_pmccntr_read();
 
@@ -241,10 +247,11 @@
 
        const uint64_t delta = n * incr_per_us;
        const uint64_t base = armreg_cntv_ct_read();
+       arm_isb();
        const uint64_t finish = base + delta;
 
        while (armreg_cntv_ct_read() < finish) {
-               /* spin */
+               arm_isb();      /* spin */
        }
 }
 
@@ -273,12 +280,16 @@
 int
 gtmr_intr(void *arg)
 {
-       const uint64_t now = armreg_cntv_ct_read();
        struct cpu_info * const ci = curcpu();
-       uint64_t delta = now - ci->ci_lastintr;
        struct clockframe * const cf = arg;
        struct gtmr_softc * const sc = &gtmr_sc;
 
+       const uint64_t now = armreg_cntv_ct_read();
+
+       arm_isb();
+
+       uint64_t delta = now - ci->ci_lastintr;
+
 #ifdef DIAGNOSTIC
        const uint64_t then = armreg_cntv_cval_read();
        struct gtmr_percpu * const pc = percpu_getref(sc->sc_percpu);
@@ -329,6 +340,9 @@
 static u_int
 gtmr_get_timecount(struct timecounter *tc)
 {
+       u_int now = (u_int) armreg_cntp_ct_read();
 
-       return (u_int) (armreg_cntp_ct_read());
+       arm_isb();      // we want the time NOW, not some instructions later.
+
+       return now;
 }