sna: Hook up a backlight udev monitor for external changes

Changes to the backlights are notified through uevents. Hooking up a
udev monitor to listen out for external changes to the backlight (e.g.
through ACPI function keys, or by the user writing to
/sys/class/backlight directly) is easier than enabling polling on the
backlight sysfs file using X's select() mechanism.

Since we listen to backlight changes, we have to be careful not to
confuse the side-effects of disabling connectors (which may cause either
ourselves or the kernel to turn off the backlight) with the user value.

Many thanks to Alexander Mezin for the suggestion to use udev for
tracking the notifications for external changes to the backlight.

Reported-by: Alexander Mezin <mezin.alexander@gmail.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=79699
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

2 files changed, 150 insertions, 4 deletions

diff --git a/src/sna/sna.h b/src/sna/sna.h
index 7845cd11..0739f7b0 100644
--- a/src/sna/sna.h
+++ b/src/sna/sna.h
@@ -298,6 +298,11 @@ struct sna {
 		unsigned serial;
 
 		uint32_t *encoders;
+
+#if HAVE_UDEV
+		struct udev_monitor *backlight_monitor;
+		pointer backlight_handler;
+#endif
 	} mode;
 
 	struct {
diff --git a/src/sna/sna_display.c b/src/sna/sna_display.c
index 2dbe3f34..c6bb9cd8 100644
--- a/src/sna/sna_display.c
+++ b/src/sna/sna_display.c
@@ -399,6 +399,129 @@ static void gem_close(int fd, uint32_t handle)
 #define BACKLIGHT_DEPRECATED_NAME  "BACKLIGHT"
 static Atom backlight_atom, backlight_deprecated_atom;
 
+#if HAVE_UDEV
+static void
+sna_backlight_uevent(int fd, void *closure)
+{
+	struct sna *sna = closure;
+	xf86CrtcConfigPtr config = XF86_CRTC_CONFIG_PTR(sna->scrn);
+	int i;
+
+	DBG(("%s()\n", __FUNCTION__));
+
+	/* Drain the event queue */
+	do {
+		struct udev_device *dev;
+
+		dev = udev_monitor_receive_device(sna->mode.backlight_monitor);
+		if (dev == NULL)
+			break;
+
+		udev_device_unref(dev);
+	} while (1);
+
+	/* Query all backlights for any changes */
+	for (i = 0; i < sna->mode.num_real_output; i++) {
+		xf86OutputPtr output = config->output[i];
+		struct sna_output *sna_output = to_sna_output(output);
+		int val;
+
+		if (sna_output->dpms_mode != DPMSModeOn)
+			continue;
+
+		assert(output->randr_output);
+
+		val = backlight_get(&sna_output->backlight);
+		if (val < 0)
+			continue;
+		DBG(("%s(%s): backlight '%s' was %d, now %d\n",
+		     __FUNCTION__, output->name, sna_output->backlight.iface,
+		     sna_output->backlight_active_level, val));
+
+		if (val == sna_output->backlight_active_level)
+			continue;
+
+		sna_output->backlight_active_level = val;
+
+		DBG(("%s(%s): sending change notification\n", __FUNCTION__, output->name));
+		RRChangeOutputProperty(output->randr_output,
+				       backlight_atom, XA_INTEGER,
+				       32, PropModeReplace, 1, &val,
+				       TRUE, FALSE);
+		RRChangeOutputProperty(output->randr_output,
+				       backlight_deprecated_atom, XA_INTEGER,
+				       32, PropModeReplace, 1, &val,
+				       TRUE, FALSE);
+	}
+}
+
+static void sna_backlight_pre_init(struct sna *sna)
+{
+	struct udev *u;
+	struct udev_monitor *mon;
+
+	u = udev_new();
+	if (!u)
+		return;
+
+	mon = udev_monitor_new_from_netlink(u, "udev");
+	if (!mon)
+		goto free_udev;
+
+	if (udev_monitor_filter_add_match_subsystem_devtype(mon, "backlight", NULL))
+		goto free_monitor;
+
+	if (udev_monitor_enable_receiving(mon))
+		goto free_monitor;
+
+	sna->mode.backlight_handler =
+		xf86AddGeneralHandler(udev_monitor_get_fd(mon),
+				      sna_backlight_uevent, sna);
+	if (!sna->mode.backlight_handler)
+		goto free_monitor;
+
+	DBG(("%s: installed backlight monitor\n", __FUNCTION__));
+	sna->mode.backlight_monitor = mon;
+
+	return;
+
+free_monitor:
+	udev_monitor_unref(mon);
+free_udev:
+	udev_unref(u);
+}
+
+static void sna_backlight_drain_uevents(struct sna *sna)
+{
+	if (sna->mode.backlight_monitor == NULL)
+		return;
+
+	sna_backlight_uevent(udev_monitor_get_fd(sna->mode.backlight_monitor),
+			     sna);
+}
+
+static void sna_backlight_close(struct sna *sna)
+{
+	struct udev *u;
+
+	if (sna->mode.backlight_handler == NULL)
+		return;
+
+	xf86RemoveGeneralHandler(sna->mode.backlight_handler);
+
+	u = udev_monitor_get_udev(sna->mode.backlight_monitor);
+	udev_monitor_unref(sna->mode.backlight_monitor);
+	udev_unref(u);
+
+	sna->mode.backlight_handler = NULL;
+	sna->mode.backlight_monitor = NULL;
+}
+#else
+static void sna_backlight_pre_init(struct sna *sna) { }
+static void sna_backlight_drain_uevents(struct sna *sna) { }
+static void sna_backlight_close(struct sna *sna) { }
+#endif
+
 static void
 sna_output_backlight_set(xf86OutputPtr output, int level)
 {
@@ -417,6 +540,12 @@ sna_output_backlight_set(xf86OutputPtr output, int level)
 			RRDeleteOutputProperty(output->randr_output, backlight_deprecated_atom);
 		}
 	}
+
+	/* Consume the uevent notification now so that we don't misconstrue
+	 * the change latter when we wake up and the output is in a different
+	 * state.
+	 */
+	sna_backlight_drain_uevents(to_sna(output->scrn));
 }
 
 static int
@@ -820,6 +949,14 @@ sna_crtc_apply(xf86CrtcPtr crtc)
 	for (i = 0; i < config->num_output; i++) {
 		xf86OutputPtr output = config->output[i];
 
+		/* Make sure we mark the output as off (and save the backlight)
+		 * before the kernel turns it off due to changing the pipe.
+		 * This is necessary as the kernel may turn off the backlight
+		 * and we lose track of the user settings.
+		 */
+		if (output->crtc == NULL)
+			output->funcs->dpms(output, DPMSModeOff);
+
 		if (output->crtc != crtc)
 			continue;
 
@@ -2374,6 +2511,7 @@ sna_output_dpms(xf86OutputPtr output, int dpms)
 {
 	struct sna *sna = to_sna(output->scrn);
 	struct sna_output *sna_output = output->driver_private;
+	int old_dpms = sna_output->dpms_mode;
 
 	DBG(("%s(%s:%d): dpms=%d (current: %d), active? %d\n",
 	     __FUNCTION__, output->name, sna_output->id,
@@ -2383,7 +2521,7 @@ sna_output_dpms(xf86OutputPtr output, int dpms)
 	if (!sna_output->id)
 		return;
 
-	if (sna_output->dpms_mode == dpms)
+	if (old_dpms == dpms)
 		return;
 
 	/* Record the value of the backlight before turning
@@ -2394,11 +2532,12 @@ sna_output_dpms(xf86OutputPtr output, int dpms)
 	 * and reapply it afterwards.
 	 */
 	if (sna_output->backlight.iface && dpms != DPMSModeOn) {
-		if (sna_output->dpms_mode == DPMSModeOn) {
+		if (old_dpms == DPMSModeOn) {
 			sna_output->backlight_active_level = sna_output_backlight_get(output);
 			DBG(("%s: saving current backlight %d\n",
 			     __FUNCTION__, sna_output->backlight_active_level));
 		}
+		sna_output->dpms_mode = dpms;
 		sna_output_backlight_set(output, 0);
 	}
 
@@ -2407,7 +2546,7 @@ sna_output_dpms(xf86OutputPtr output, int dpms)
 					sna_output->id,
 					sna_output->dpms_id,
 					dpms))
-		dpms = sna_output->dpms_mode;
+		dpms = old_dpms;
 
 	if (sna_output->backlight.iface && dpms == DPMSModeOn) {
 		DBG(("%s: restoring previous backlight %d\n",
@@ -2577,9 +2716,9 @@ sna_output_set_property(xf86OutputPtr output, Atom property,
 		if (val < 0 || val > sna_output->backlight.max)
 			return FALSE;
 
+		sna_output->backlight_active_level = val;
 		if (sna_output->dpms_mode == DPMSModeOn)
 			sna_output_backlight_set(output, val);
-		sna_output->backlight_active_level = val;
 		return TRUE;
 	}
 
@@ -4736,6 +4875,7 @@ bool sna_mode_pre_init(ScrnInfoPtr scrn, struct sna *sna)
 		drmModeFreeResources(res);
 
 		sna_cursor_pre_init(sna);
+		sna_backlight_pre_init(sna);
 	} else {
 		if (num_fake == 0)
 			num_fake = 1;
@@ -4772,6 +4912,7 @@ sna_mode_close(struct sna *sna)
 	if (sna->flags & SNA_IS_HOSTED)
 		return;
 
+	sna_backlight_close(sna);
 	sna_cursor_close(sna);
 
 	for (i = 0; i < sna->mode.num_real_crtc; i++)