backend: add get_present_clock

backend/backend.c

@@ -64,6 +64,13 @@ struct wlr_session *wlr_backend_get_session(struct wlr_backend *backend) {
 	return NULL;
 }
 
+clockid_t wlr_backend_get_present_clock(struct wlr_backend *backend) {
+	if (backend->impl->get_present_clock) {
+		return backend->impl->get_present_clock(backend);
+	}
+	return CLOCK_MONOTONIC;
+}
+
 static size_t parse_outputs_env(const char *name) {
 	const char *outputs_str = getenv(name);
 	if (outputs_str == NULL) {

backend/drm/backend.c

@@ -65,10 +65,16 @@ static struct wlr_renderer *backend_get_renderer(
 	}
 }
 
+static clockid_t backend_get_present_clock(struct wlr_backend *backend) {
+	struct wlr_drm_backend *drm = get_drm_backend_from_backend(backend);
+	return drm->clock;
+}
+
 static struct wlr_backend_impl backend_impl = {
 	.start = backend_start,
 	.destroy = backend_destroy,
 	.get_renderer = backend_get_renderer,
+	.get_present_clock = backend_get_present_clock,
 };
 
 bool wlr_backend_is_drm(struct wlr_backend *b) {

backend/drm/drm.c

@@ -1,3 +1,4 @@
+#define _POSIX_C_SOURCE 199309L
 #include <assert.h>
 #include <drm_mode.h>
 #include <EGL/egl.h>
@@ -27,8 +28,8 @@
 #include "util/signal.h"
 
 bool check_drm_features(struct wlr_drm_backend *drm) {
-	if (drm->parent) {
 	uint64_t cap;
+	if (drm->parent) {
 		if (drmGetCap(drm->fd, DRM_CAP_PRIME, &cap) ||
 				!(cap & DRM_PRIME_CAP_IMPORT)) {
 			wlr_log(WLR_ERROR,
@@ -51,16 +52,21 @@ bool check_drm_features(struct wlr_drm_backend *drm) {
 
 	const char *no_atomic = getenv("WLR_DRM_NO_ATOMIC");
 	if (no_atomic && strcmp(no_atomic, "1") == 0) {
-		wlr_log(WLR_DEBUG, "WLR_DRM_NO_ATOMIC set, forcing legacy DRM interface");
+		wlr_log(WLR_DEBUG,
+			"WLR_DRM_NO_ATOMIC set, forcing legacy DRM interface");
 		drm->iface = &legacy_iface;
 	} else if (drmSetClientCap(drm->fd, DRM_CLIENT_CAP_ATOMIC, 1)) {
-		wlr_log(WLR_DEBUG, "Atomic modesetting unsupported, using legacy DRM interface");
+		wlr_log(WLR_DEBUG,
+			"Atomic modesetting unsupported, using legacy DRM interface");
 		drm->iface = &legacy_iface;
 	} else {
 		wlr_log(WLR_DEBUG, "Using atomic DRM interface");
 		drm->iface = &atomic_iface;
 	}
 
+	int ret = drmGetCap(drm->fd, DRM_CAP_TIMESTAMP_MONOTONIC, &cap);
+	drm->clock = (ret == 0 && cap == 1) ? CLOCK_MONOTONIC : CLOCK_REALTIME;
+
 	return true;
 }
 

include/backend/drm/drm.h

@@ -6,6 +6,7 @@
 #include <stdbool.h>
 #include <stddef.h>
 #include <stdint.h>
+#include <time.h>
 #include <wayland-server.h>
 #include <wayland-util.h>
 #include <wlr/backend/drm.h>
@@ -67,6 +68,7 @@ struct wlr_drm_backend {
 
 	struct wlr_drm_backend *parent;
 	const struct wlr_drm_interface *iface;
+	clockid_t clock;
 
 	int fd;
 

include/wlr/backend.h

@@ -62,5 +62,9 @@ struct wlr_renderer *wlr_backend_get_renderer(struct wlr_backend *backend);
  * Might return NULL for backends that don't use a session.
  */
 struct wlr_session *wlr_backend_get_session(struct wlr_backend *backend);
+/**
+ * Returns the clock used by the backend for presentation feedback.
+ */
+clockid_t wlr_backend_get_present_clock(struct wlr_backend *backend);
 
 #endif

include/wlr/backend/interface.h

@@ -10,6 +10,7 @@
 #define WLR_BACKEND_INTERFACE_H
 
 #include <stdbool.h>
+#include <time.h>
 #include <wlr/backend.h>
 #include <wlr/render/egl.h>
 
@@ -18,6 +19,7 @@ struct wlr_backend_impl {
 	void (*destroy)(struct wlr_backend *backend);
 	struct wlr_renderer *(*get_renderer)(struct wlr_backend *backend);
 	struct wlr_session *(*get_session)(struct wlr_backend *backend);
+	clockid_t (*get_present_clock)(struct wlr_backend *backend);
 };
 
 /**

types/wlr_output.c

@@ -18,8 +18,6 @@
 
 #define OUTPUT_VERSION 3
 
-#define DEFAULT_PRESENT_CLOCK CLOCK_MONOTONIC
-
 static void output_send_to_resource(struct wl_resource *resource) {
 	struct wlr_output *output = wlr_output_from_resource(resource);
 	const uint32_t version = wl_resource_get_version(resource);
@@ -268,6 +266,7 @@ void wlr_output_init(struct wlr_output *output, struct wlr_backend *backend,
 	wl_signal_init(&output->events.frame);
 	wl_signal_init(&output->events.needs_swap);
 	wl_signal_init(&output->events.swap_buffers);
+	wl_signal_init(&output->events.present);
 	wl_signal_init(&output->events.enable);
 	wl_signal_init(&output->events.mode);
 	wl_signal_init(&output->events.scale);
@@ -566,7 +565,8 @@ void wlr_output_send_present(struct wlr_output *output, struct timespec *when,
 		unsigned seq, uint32_t flags) {
 	struct timespec now;
 	if (when == NULL) {
-		if (!clock_gettime(DEFAULT_PRESENT_CLOCK, &now)) {
+		clockid_t clock = wlr_backend_get_present_clock(output->backend);
+		if (!clock_gettime(clock, &now)) {
 			wlr_log_errno(WLR_ERROR, "failed to send output present event: "
 				"failed to read clock");
 			return;