[RFC PATCH v2 2/5] hw/misc/led: Add LED_STATUS_CHANGED QAPI event

["Philippe Mathieu-Daudé" <f4bug@amsat.org>]

Allow LED devices to emit STATUS_CHANGED events on a QMP chardev.

QMP event examples:

{
    "timestamp": {
        "seconds": 1591704274,
        "microseconds": 520850
    },
    "event": "LED_STATUS_CHANGED",
    "data": {
        "name": "Green LED #0",
        "status": "on"
    }
}
{
    "timestamp": {
        "seconds": 1591704275,
        "microseconds": 530912
    },
    "event": "LED_STATUS_CHANGED",
    "data": {
        "name": "Green LED #0",
        "status": "off"
    }
}

Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
---
Since v1: rate limit 4/sec (eblake)
---
 qapi/led.json         | 47 +++++++++++++++++++++++++++++++++++++++++++
 qapi/qapi-schema.json |  1 +
 include/hw/misc/led.h |  1 +
 hw/misc/led.c         | 24 +++++++++++++++++++++-
 MAINTAINERS           |  1 +
 qapi/Makefile.objs    |  2 +-
 6 files changed, 74 insertions(+), 2 deletions(-)
 create mode 100644 qapi/led.json

diff --git a/qapi/led.json b/qapi/led.json
new file mode 100644
index 0000000000..b6cef8a5dd
--- /dev/null
+++ b/qapi/led.json
@@ -0,0 +1,47 @@
+# -*- Mode: Python -*-
+#
+
+##
+# = LED device
+##
+
+##
+# @LedState:
+#
+# Status of a LED
+#
+# @on: device is emitting
+#
+# @off: device is off
+#
+# Since: 5.1
+##
+{ 'enum': 'LedState', 'data': [ 'on', 'off' ] }
+
+##
+# @LED_STATUS_CHANGED:
+#
+# Emitted when LED status changed
+#
+# @name: LED description
+#
+# @status: New status
+#
+# Since: 5.1
+#
+# Example:
+#
+# <- {"timestamp": {"seconds": 1541579657, "microseconds": 986760},
+#     "event": "LED_STATUS_CHANGED",
+#     "data":
+#         {"name": "Blue LED #3",
+#          "status": "on"
+#         }
+#    }
+#
+##
+{ 'event': 'LED_STATUS_CHANGED',
+  'data': { 'name'      : 'str',
+            'status'    : 'LedState'
+          }
+}
diff --git a/qapi/qapi-schema.json b/qapi/qapi-schema.json
index 43b0ba0dea..6f3ffc0ae1 100644
--- a/qapi/qapi-schema.json
+++ b/qapi/qapi-schema.json
@@ -84,3 +84,4 @@
 { 'include': 'misc.json' }
 { 'include': 'misc-target.json' }
 { 'include': 'audio.json' }
+{ 'include': 'led.json' }
diff --git a/include/hw/misc/led.h b/include/hw/misc/led.h
index 427ca1418e..9300d4db6c 100644
--- a/include/hw/misc/led.h
+++ b/include/hw/misc/led.h
@@ -21,6 +21,7 @@ typedef struct LEDState {
 
     qemu_irq irq;
     uint8_t current_state;
+    int64_t last_event_ms;
 
     /* Properties */
     char *name;
diff --git a/hw/misc/led.c b/hw/misc/led.c
index 1bae1a34c0..11c7e8bb89 100644
--- a/hw/misc/led.c
+++ b/hw/misc/led.c
@@ -7,18 +7,40 @@
  */
 #include "qemu/osdep.h"
 #include "qapi/error.h"
+#include "qapi/qapi-events-led.h"
+#include "qemu/timer.h"
 #include "migration/vmstate.h"
 #include "hw/qdev-properties.h"
 #include "hw/misc/led.h"
 #include "hw/irq.h"
 #include "trace.h"
 
+#define MAX_QMP_LED_EVENTS_PER_SEC  4 /* TODO shared between LED children? */
+
+static void emit_led_status_changed_event(LEDState *s, int state)
+{
+    static const int64_t delay_min_ms = NANOSECONDS_PER_SECOND / SCALE_MS
+                                        / MAX_QMP_LED_EVENTS_PER_SEC;
+    int64_t now = qemu_clock_get_ms(QEMU_CLOCK_REALTIME);
+
+    if (now - s->last_event_ms > delay_min_ms) {
+        qapi_event_send_led_status_changed(s->name, state
+                                                    ? LED_STATE_ON
+                                                    : LED_STATE_OFF);
+    } else {
+        /* TODO count skipped events? */
+    }
+    s->last_event_ms = now;
+}
+
 static void led_set(void *opaque, int line, int new_state)
 {
     LEDState *s = LED(opaque);
 
     trace_led_set(s->name, s->current_state, new_state);
-
+    if (new_state != s->current_state) {
+        emit_led_status_changed_event(s, new_state);
+    }
     s->current_state = new_state;
 }
 
diff --git a/MAINTAINERS b/MAINTAINERS
index 10593863dc..266b07c4b4 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -1860,6 +1860,7 @@ F: stubs/vmgenid.c
 LED
 M: Philippe Mathieu-Daudé <f4bug@amsat.org>
 S: Maintained
+F: qapi/led.json
 F: include/hw/misc/led.h
 F: hw/misc/led.c
 
diff --git a/qapi/Makefile.objs b/qapi/Makefile.objs
index 4673ab7490..e9f6570c32 100644
--- a/qapi/Makefile.objs
+++ b/qapi/Makefile.objs
@@ -6,7 +6,7 @@ util-obj-y += qmp-event.o
 util-obj-y += qapi-util.o
 
 QAPI_COMMON_MODULES = audio authz block-core block char common control crypto
-QAPI_COMMON_MODULES += dump error introspect job machine migration misc
+QAPI_COMMON_MODULES += dump error introspect job led machine migration misc
 QAPI_COMMON_MODULES += net pragma qdev qom rdma rocker run-state sockets tpm
 QAPI_COMMON_MODULES += trace transaction ui
 QAPI_TARGET_MODULES = machine-target misc-target
-- 
2.21.3