clock: Add ClockEvent parameter to callbacks

The Clock framework allows users to specify a callback which is
called after the clock's period has been updated.  Some users need to
also have a callback which is called before the clock period is
updated.

As the first step in adding support for notifying Clock users on
pre-update events, add an argument to the ClockCallback to specify
what event is being notified, and add an argument to the various
functions for registering a callback to specify which events are
of interest to that callback.

Note that the documentation update renders correct the previously
incorrect claim in 'Adding a new clock' that callbacks "will be
explained in a following section".

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Luc Michel <luc@lmichel.fr>
Tested-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20210219144617.4782-2-peter.maydell@linaro.org

1 files changed, 17 insertions, 4 deletions

diff --git a/hw/core/clock.c b/hw/core/clock.c
index 76b5f468b6..4479eff145 100644
--- a/hw/core/clock.c
+++ b/hw/core/clock.c
@@ -39,15 +39,17 @@ Clock *clock_new(Object *parent, const char *name)
     return clk;
 }
 
-void clock_set_callback(Clock *clk, ClockCallback *cb, void *opaque)
+void clock_set_callback(Clock *clk, ClockCallback *cb, void *opaque,
+                        unsigned int events)
 {
     clk->callback = cb;
     clk->callback_opaque = opaque;
+    clk->callback_events = events;
 }
 
 void clock_clear_callback(Clock *clk)
 {
-    clock_set_callback(clk, NULL, NULL);
+    clock_set_callback(clk, NULL, NULL, 0);
 }
 
 bool clock_set(Clock *clk, uint64_t period)
@@ -62,6 +64,17 @@ bool clock_set(Clock *clk, uint64_t period)
     return true;
 }
 
+static void clock_call_callback(Clock *clk, ClockEvent event)
+{
+    /*
+     * Call the Clock's callback for this event, if it has one and
+     * is interested in this event.
+     */
+    if (clk->callback && (clk->callback_events & event)) {
+        clk->callback(clk->callback_opaque, event);
+    }
+}
+
 static void clock_propagate_period(Clock *clk, bool call_callbacks)
 {
     Clock *child;
@@ -72,8 +85,8 @@ static void clock_propagate_period(Clock *clk, bool call_callbacks)
             trace_clock_update(CLOCK_PATH(child), CLOCK_PATH(clk),
                                CLOCK_PERIOD_TO_HZ(clk->period),
                                call_callbacks);
-            if (call_callbacks && child->callback) {
-                child->callback(child->callback_opaque);
+            if (call_callbacks) {
+                clock_call_callback(child, ClockUpdate);
             }
             clock_propagate_period(child, call_callbacks);
         }