[src/trunk]: src/sys/arch Workaround A-008585 errata in GTMR.

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

details:   https://anonhg.NetBSD.org/src/rev/f8eb5c349e6e
branches:  trunk
changeset: 322725:f8eb5c349e6e
user:      joerg <joerg%NetBSD.org@localhost>
date:      Mon May 14 17:15:54 2018 +0000

description:
Workaround A-008585 errata in GTMR.

Register reads and writes may provide unstable results if the counter
hardware is active at the same time. This results in non-monotonic
counters seen by both the gtmr interrupt and time counter.

The loops are currently applied unconditionally, restricting them to
appropiate FDT markers can be applied later.

diffstat:

 sys/arch/aarch64/include/armreg.h |   9 ++++-
 sys/arch/arm/cortex/gtmr.c        |  67 +++++++++++++++++++++++++++++++++-----
 sys/arch/arm/include/armreg.h     |   9 ++++-
 3 files changed, 73 insertions(+), 12 deletions(-)

diffs (181 lines):

diff -r 79338545adca -r f8eb5c349e6e sys/arch/aarch64/include/armreg.h
--- a/sys/arch/aarch64/include/armreg.h Mon May 14 17:11:38 2018 +0000
+++ b/sys/arch/aarch64/include/armreg.h Mon May 14 17:15:54 2018 +0000
@@ -1,4 +1,4 @@
-/* $NetBSD: armreg.h,v 1.9 2018/04/01 04:35:03 ryo Exp $ */
+/* $NetBSD: armreg.h,v 1.10 2018/05/14 17:15:54 joerg Exp $ */
 
 /*-
  * Copyright (c) 2014 The NetBSD Foundation, Inc.
@@ -1005,6 +1005,13 @@
 /*
  * Counter-timer Virtual Timer TimerValue register
  */
+static inline uint32_t
+gtmr_cntv_tval_read(void)
+{
+
+       return reg_cntv_tval_el0_read();
+}
+
 static inline void
 gtmr_cntv_tval_write(uint32_t val)
 {
diff -r 79338545adca -r f8eb5c349e6e sys/arch/arm/cortex/gtmr.c
--- a/sys/arch/arm/cortex/gtmr.c        Mon May 14 17:11:38 2018 +0000
+++ b/sys/arch/arm/cortex/gtmr.c        Mon May 14 17:15:54 2018 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: gtmr.c,v 1.26 2018/05/14 17:11:38 joerg Exp $  */
+/*     $NetBSD: gtmr.c,v 1.27 2018/05/14 17:15:54 joerg Exp $  */
 
 /*-
  * Copyright (c) 2012 The NetBSD Foundation, Inc.
@@ -30,7 +30,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: gtmr.c,v 1.26 2018/05/14 17:11:38 joerg Exp $");
+__KERNEL_RCSID(0, "$NetBSD: gtmr.c,v 1.27 2018/05/14 17:15:54 joerg Exp $");
 
 #include <sys/param.h>
 #include <sys/bus.h>
@@ -50,6 +50,51 @@
 #include <arm/cortex/gtmr_var.h>
 #include <arm/cortex/mpcore_var.h>
 
+#define stable_write(reg) \
+static void \
+reg ## _stable_write(struct gtmr_softc *sc, uint64_t val) \
+{ \
+       static int max_retry = 0; \
+       int retry; \
+       reg ## _write(val); \
+       retry = 0; \
+       while (reg ## _read() != (val) && retry++ < 200) \
+               reg ## _write(val); \
+       if (retry > max_retry) { \
+               aprint_verbose_dev(sc->sc_dev, #reg "_write max retries %d -> %d\n", \
+                   max_retry, retry); \
+               max_retry = retry; \
+       } \
+}
+
+stable_write(gtmr_cntv_tval);
+
+#define stable_read(reg) \
+static uint64_t \
+reg ## _stable_read(struct gtmr_softc *sc) \
+{ \
+       static int max_retry = 0; \
+       uint64_t oval, val; \
+       int retry = 0; \
+       val = reg ## _read(); \
+       while (++retry < 200) { \
+               oval = val; \
+               val = reg ## _read(); \
+               if (val == oval) \
+                       break; \
+       } \
+       if (retry > max_retry) { \
+               aprint_verbose_dev(sc->sc_dev, #reg "_read max retries %d -> %d\n", \
+                   max_retry, retry); \
+               max_retry = retry; \
+       } \
+       return val; \
+}
+
+stable_read(gtmr_cntv_cval);
+stable_read(gtmr_cntvct);
+stable_read(gtmr_cntpct);
+
 static int gtmr_match(device_t, cfdata_t, void *);
 static void gtmr_attach(device_t, device_t, void *);
 
@@ -150,6 +195,7 @@
 
        gtmr_timecounter.tc_name = device_xname(sc->sc_dev);
        gtmr_timecounter.tc_frequency = sc->sc_freq;
+       gtmr_timecounter.tc_priv = sc;
 
        tc_init(&gtmr_timecounter);
 
@@ -177,8 +223,8 @@
         * Get now and update the compare timer.
         */
        arm_isb();
-       ci->ci_lastintr = gtmr_cntvct_read();
-       gtmr_cntv_tval_write(sc->sc_autoinc);
+       ci->ci_lastintr = gtmr_cntvct_stable_read(sc);
+       gtmr_cntv_tval_stable_write(sc, sc->sc_autoinc);
        splx(s);
        KASSERT(gtmr_cntvct_read() != 0);
 }
@@ -210,11 +256,11 @@
        unsigned int delta = 0, usecs = 0;
 
        arm_isb();
-       uint64_t last = gtmr_cntpct_read();
+       uint64_t last = gtmr_cntpct_stable_read(sc);
 
        while (n > usecs) {
                arm_isb();
-               uint64_t curr = gtmr_cntpct_read();
+               uint64_t curr = gtmr_cntpct_stable_read(sc);
                if (curr < last)
                        delta += curr + (UINT64_MAX - last);
                else
@@ -246,11 +292,11 @@
        if ((ctl & CNTCTL_ISTATUS) == 0)
                return 0;
 
-       const uint64_t now = gtmr_cntvct_read();
+       const uint64_t now = gtmr_cntvct_stable_read(sc);
        uint64_t delta = now - ci->ci_lastintr;
 
 #ifdef DIAGNOSTIC
-       const uint64_t then = gtmr_cntv_cval_read();
+       const uint64_t then = gtmr_cntv_cval_stable_read(sc);
        struct gtmr_percpu * const pc = percpu_getref(sc->sc_percpu);
        KASSERTMSG(then <= now, "%"PRId64, now - then);
        KASSERTMSG(then + pc->pc_delta >= ci->ci_lastintr + sc->sc_autoinc,
@@ -271,7 +317,7 @@
        } else {
                delta = 0;
        }
-       gtmr_cntv_tval_write(sc->sc_autoinc - delta);
+       gtmr_cntv_tval_stable_write(sc, sc->sc_autoinc - delta);
 
        ci->ci_lastintr = now;
 
@@ -296,6 +342,7 @@
 static u_int
 gtmr_get_timecount(struct timecounter *tc)
 {
+       struct gtmr_softc * const sc = tc->tc_priv;
        arm_isb();      // we want the time NOW, not some instructions later.
-       return (u_int) gtmr_cntpct_read();
+       return (u_int) gtmr_cntpct_stable_read(sc);
 }
diff -r 79338545adca -r f8eb5c349e6e sys/arch/arm/include/armreg.h
--- a/sys/arch/arm/include/armreg.h     Mon May 14 17:11:38 2018 +0000
+++ b/sys/arch/arm/include/armreg.h     Mon May 14 17:15:54 2018 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: armreg.h,v 1.120 2018/04/01 04:35:04 ryo Exp $ */
+/*     $NetBSD: armreg.h,v 1.121 2018/05/14 17:15:54 joerg Exp $       */
 
 /*
  * Copyright (c) 1998, 2001 Ben Harris
@@ -969,6 +969,13 @@
 /*
  * Counter-timer Virtual Timer TimerValue register
  */
+static inline uint32_t
+gtmr_cntv_tval_read(void)
+{
+
+       return armreg_cntv_tval_read();
+}
+
 static inline void
 gtmr_cntv_tval_write(uint32_t val)
 {