[WESTON PATCH 2/2] compositor-drm: Watchdog timer implementation

[Frederic Plourde]

Weston will not repaint until previous update has been acked by
a page-flip event coming from the drm driver. However, some buggy drivers
won't return those events or will stop sending them at some point and
Weston output repaints will completely freeze. To ease developers' task in
testing their drivers, this patch makes compositor-drm use a watchdog timer
to detect cases where those page-flip events stop coming.

This watchdog timer (WDT) implementation is software only and includes
basic features usually found in a WDT. We simply exit Weston gracefully
with an exit code when the dog barks.

The watchdog timeout value can be set via weston.ini by adding a
watchdog-timer-timeout=<SECONDS> entry under a new [compositor-drm]
section. Setting this timeout to 0 disables the watchdog feature.

https://bugs.freedesktop.org/show_bug.cgi?id=83884
---
 src/compositor-drm.c | 100 +++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 100 insertions(+)

diff --git a/src/compositor-drm.c b/src/compositor-drm.c
index 07b83a7..f9fb673 100644
--- a/src/compositor-drm.c
+++ b/src/compositor-drm.c
@@ -122,6 +122,8 @@ struct drm_compositor {
 
 	uint32_t cursor_width;
 	uint32_t cursor_height;
+
+	uint32_t watchdog_timer_timeout;
 };
 
 struct drm_mode {
@@ -183,6 +185,11 @@ struct drm_output {
 
 	struct vaapi_recorder *recorder;
 	struct wl_listener recorder_frame_listener;
+
+	struct watchdog_timer {
+		struct wl_event_source *timer;
+		uint32_t timeout;
+	} wdt;
 };
 
 /*
@@ -221,6 +228,57 @@ static struct gl_renderer_interface *gl_renderer;
 
 static const char default_seat[] = "seat0";
 
+/* Creates a watchdog timer. Note that timer is not armed by default */
+static int
+drm_output_watchdog_timer_create(struct watchdog_timer *wdt, struct wl_display *display,
+					  wl_event_loop_timer_func_t timeout_func, void *timer_arg,
+					  uint32_t timeout)
+{
+	struct wl_event_loop *loop = NULL;
+
+	loop = wl_display_get_event_loop(display);
+	if (loop) {
+		wdt->timer = wl_event_loop_add_timer(loop,
+											 timeout_func, timer_arg);
+		if (wdt->timer) {
+			wdt->timeout = timeout;
+			return 0;
+		}
+	}
+
+	return -1;
+}
+
+/* Start/reset/arm the dog's timer. This can also be used to 'pat' the dog */
+static int
+drm_output_watchdog_timer_start(struct watchdog_timer *wdt)
+{
+	if (wdt->timer)
+		return wl_event_source_timer_update(wdt->timer, wdt->timeout);
+
+	return -1;
+}
+
+/* Disarms the watchdog */
+static int
+drm_output_watchdog_timer_stop(struct watchdog_timer *wdt)
+{
+	if (wdt->timer)
+		return wl_event_source_timer_update(wdt->timer, 0);
+
+	return -1;
+}
+
+static void
+drm_output_watchdog_timer_destroy(struct watchdog_timer *wdt)
+{
+	if (wdt->timer) {
+		wl_event_source_remove(wdt->timer);
+	}
+
+	wdt->timer = NULL;
+}
+
 static void
 drm_output_set_cursor(struct drm_output *output);
 
@@ -591,6 +649,20 @@ drm_output_set_gamma(struct weston_output *output_base,
 		weston_log("set gamma failed: %m\n");
 }
 
+static void
+drm_output_watchdog_bark(void *output) {
+	/*
+	* Our watchdog just barked at us, means we're not receiving drm
+	* page flip events anymore for that output. Let's gracefully exit
+	* weston with a return value so devs can debug what's going on.
+	*/
+	struct drm_output *out = (struct drm_output *) output;
+	struct weston_compositor *compositor =
+		(struct weston_compositor *) out->base.compositor;
+
+	weston_compositor_exit_with_code(compositor, EXIT_FAILURE);
+}
+
 static int
 drm_output_repaint(struct weston_output *output_base,
 		   pixman_region32_t *damage)
@@ -624,6 +696,13 @@ drm_output_repaint(struct weston_output *output_base,
 		output_base->set_dpms(output_base, WESTON_DPMS_ON);
 	}
 
+	/* Start out watchdog timer */
+	if (output->wdt.timer) {
+		if (drm_output_watchdog_timer_start(&output->wdt)) {
+			weston_log("failed to start drm watchdog: %m\n");
+		}
+	}
+
 	if (drmModePageFlip(compositor->drm.fd, output->crtc_id,
 			    output->next->fb_id,
 			    DRM_MODE_PAGE_FLIP_EVENT, output) < 0) {
@@ -781,6 +860,10 @@ page_flip_handler(int fd, unsigned int frame,
 
 	output->page_flip_pending = 0;
 
+	/* Stop the watchdog instead of patting it here */
+	if (output->wdt.timer)
+		drm_output_watchdog_timer_stop(&output->wdt);
+
 	if (output->destroy_pending)
 		drm_output_destroy(&output->base);
 	else if (!output->vblank_pending) {
@@ -1176,6 +1259,8 @@ drm_output_destroy(struct weston_output *output_base)
 		gbm_surface_destroy(output->surface);
 	}
 
+	drm_output_watchdog_timer_destroy(&output->wdt);
+
 	weston_plane_release(&output->fb_plane);
 	weston_plane_release(&output->cursor_plane);
 
@@ -2013,6 +2098,17 @@ create_output_for_connector(struct drm_compositor *ec,
 
 	output->crtc_id = resources->crtcs[i];
 	output->pipe = i;
+
+	output->wdt.timer = NULL;
+	if (ec->watchdog_timer_timeout) {
+		if (drm_output_watchdog_timer_create(&output->wdt,
+			   ec->base.wl_display, (wl_event_loop_timer_func_t)
+			   drm_output_watchdog_bark, output,
+			   ec->watchdog_timer_timeout)) {
+			weston_log("creating drm watchdog timer failed: %m\n");
+		}
+	}
+
 	ec->crtc_allocator |= (1 << output->crtc_id);
 	output->connector_id = connector->connector_id;
 	ec->connector_allocator |= (1 << output->connector_id);
@@ -2786,6 +2882,10 @@ drm_compositor_create(struct wl_display *display,
 					&ec->format) == -1)
 		goto err_base;
 
+	section = weston_config_get_section(config, "compositor-drm", NULL, NULL);
+	weston_config_section_get_uint(section, "watchdog-timer-timeout",
+									 &ec->watchdog_timer_timeout, 0);
+
 	ec->use_pixman = param->use_pixman;
 
 	if (weston_compositor_init(&ec->base, display, argc, argv,
-- 
1.9.1