3 files changed, 22 insertions, 3 deletions
diff --git a/backend/backend.c b/backend/backend.c
index 2d6464b7..b8cf8797 100644
--- a/backend/backend.c
+++ b/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) {
diff --git a/backend/drm/backend.c b/backend/drm/backend.c
index b298365e..b230613d 100644
--- a/backend/drm/backend.c
+++ b/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) {
diff --git a/backend/drm/drm.c b/backend/drm/drm.c
index ace0835e..753b6ab8 100644
--- a/backend/drm/drm.c
+++ 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) {
+	uint64_t cap;
 	if (drm->parent) {
-		uint64_t cap;
 		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;
 }