[src/trunk]: src/sys/arch/xen/xen xen_clock(4): Fix whitespace and sprinkle c...

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

details:   https://anonhg.NetBSD.org/src/rev/324b01330a50
branches:  trunk
changeset: 378257:324b01330a50
user:      riastradh <riastradh%NetBSD.org@localhost>
date:      Fri Jul 28 10:38:44 2023 +0000

description:
xen_clock(4): Fix whitespace and sprinkle comments.

No functional change intended.

diffstat:

 sys/arch/xen/xen/xen_clock.c |  40 +++++++++++++++++++++++++++++++++++-----
 1 files changed, 35 insertions(+), 5 deletions(-)

diffs (93 lines):

diff -r ce2f07b55629 -r 324b01330a50 sys/arch/xen/xen/xen_clock.c
--- a/sys/arch/xen/xen/xen_clock.c      Fri Jul 28 10:37:28 2023 +0000
+++ b/sys/arch/xen/xen/xen_clock.c      Fri Jul 28 10:38:44 2023 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: xen_clock.c,v 1.12 2023/07/17 10:12:54 bouyer Exp $    */
+/*     $NetBSD: xen_clock.c,v 1.13 2023/07/28 10:38:44 riastradh Exp $ */
 
 /*-
  * Copyright (c) 2017, 2018 The NetBSD Foundation, Inc.
@@ -36,7 +36,7 @@
 #endif
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: xen_clock.c,v 1.12 2023/07/17 10:12:54 bouyer Exp $");
+__KERNEL_RCSID(0, "$NetBSD: xen_clock.c,v 1.13 2023/07/28 10:38:44 riastradh Exp $");
 
 #include <sys/param.h>
 #include <sys/types.h>
@@ -673,11 +673,31 @@ xen_suspendclocks(struct cpu_info *ci)
        KASSERT(ci == curcpu());
        KASSERT(kpreempt_disabled());
 
+       /*
+        * Find the VIRQ_TIMER event channel and close it so new timer
+        * interrupt events stop getting delivered to it.
+        *
+        * XXX Should this happen later?  This is not the reverse order
+        * of xen_resumeclocks.  It is apparently necessary in this
+        * order only because we don't stash evtchn anywhere, but we
+        * could stash it.
+        */
        evtch = unbind_virq_from_evtch(VIRQ_TIMER);
        KASSERT(evtch != -1);
 
+       /*
+        * Mask the event channel so we stop getting new interrupts on
+        * it.
+        */
        hypervisor_mask_event(evtch);
-       event_remove_handler(evtch, 
+
+       /*
+        * Now that we are no longer getting new interrupts, remove the
+        * handler and wait for any existing calls to the handler to
+        * complete.  After this point, there can be no concurrent
+        * calls to xen_timer_handler.
+        */
+       event_remove_handler(evtch,
            __FPTRCAST(int (*)(void *), xen_timer_handler), ci);
 
        aprint_verbose("Xen clock: removed event channel %d\n", evtch);
@@ -705,9 +725,16 @@ xen_resumeclocks(struct cpu_info *ci)
        KASSERT(ci == curcpu());
        KASSERT(kpreempt_disabled());
 
+       /*
+        * Allocate an event channel to receive VIRQ_TIMER events.
+        */
        evtch = bind_virq_to_evtch(VIRQ_TIMER);
        KASSERT(evtch != -1);
 
+       /*
+        * Set an event handler for VIRQ_TIMER events to call
+        * xen_timer_handler.
+        */
        snprintf(intr_xname, sizeof(intr_xname), "%s clock",
            device_xname(ci->ci_dev));
        /* XXX sketchy function pointer cast -- fix the API, please */
@@ -716,7 +743,6 @@ xen_resumeclocks(struct cpu_info *ci)
            ci, IPL_CLOCK, NULL, intr_xname, true, ci) == NULL)
                panic("failed to establish timer interrupt handler");
 
-
        aprint_verbose("Xen %s: using event channel %d\n", intr_xname, evtch);
 
        /* Disarm the periodic timer on Xen>=3.1 which is allegedly buggy.  */
@@ -729,11 +755,15 @@ xen_resumeclocks(struct cpu_info *ci)
        /* Pretend the last hardclock happened right now.  */
        ci->ci_xen_hardclock_systime_ns = xen_vcputime_systime_ns();
 
-
        /* Arm the one-shot timer.  */
        error = HYPERVISOR_set_timer_op(ci->ci_xen_hardclock_systime_ns +
            NS_PER_TICK);
        KASSERT(error == 0);
+
+       /*
+        * Ready to go.  Unmask the event.  After this point, Xen may
+        * start calling xen_timer_handler.
+        */
        hypervisor_unmask_event(evtch);
 
        /* We'd better not have switched CPUs.  */