backend: drop wlr_backend_get_presentation_clock()

We can just assume CLOCK_MONOTONIC everywhere.

Simplifies the backend API, and fixes clock mismatches when multiple
backends are used together with different clocks.

2 files changed, 6 insertions, 10 deletions

diff --git a/backend/drm/backend.c b/backend/drm/backend.c
index df02c6b3..4ee79773 100644
--- a/backend/drm/backend.c
+++ b/backend/drm/backend.c
@@ -64,11 +64,6 @@ static void backend_destroy(struct wlr_backend *backend) {
 	free(drm);
 }
 
-static clockid_t backend_get_presentation_clock(struct wlr_backend *backend) {
-	struct wlr_drm_backend *drm = get_drm_backend_from_backend(backend);
-	return drm->clock;
-}
-
 static int backend_get_drm_fd(struct wlr_backend *backend) {
 	struct wlr_drm_backend *drm = get_drm_backend_from_backend(backend);
 
@@ -86,7 +81,6 @@ static uint32_t drm_backend_get_buffer_caps(struct wlr_backend *backend) {
 static const struct wlr_backend_impl backend_impl = {
 	.start = backend_start,
 	.destroy = backend_destroy,
-	.get_presentation_clock = backend_get_presentation_clock,
 	.get_drm_fd = backend_get_drm_fd,
 	.get_buffer_caps = drm_backend_get_buffer_caps,
 };
diff --git a/backend/drm/drm.c b/backend/drm/drm.c
index 3db27749..f7c33690 100644
--- a/backend/drm/drm.c
+++ b/backend/drm/drm.c
@@ -80,6 +80,11 @@ bool check_drm_features(struct wlr_drm_backend *drm) {
 		return false;
 	}
 
+	if (drmGetCap(drm->fd, DRM_CAP_TIMESTAMP_MONOTONIC, &cap) || !cap) {
+		wlr_log(WLR_ERROR, "DRM_CAP_TIMESTAMP_MONOTONIC unsupported");
+		return false;
+	}
+
 	if (env_parse_bool("WLR_DRM_FORCE_LIBLIFTOFF")) {
 #if HAVE_LIBLIFTOFF
 		wlr_log(WLR_INFO,
@@ -110,13 +115,10 @@ bool check_drm_features(struct wlr_drm_backend *drm) {
 		drm->supports_tearing_page_flips = drmGetCap(drm->fd, DRM_CAP_ASYNC_PAGE_FLIP, &cap) == 0 && cap == 1;
 	}
 
-	int ret = drmGetCap(drm->fd, DRM_CAP_TIMESTAMP_MONOTONIC, &cap);
-	drm->clock = (ret == 0 && cap == 1) ? CLOCK_MONOTONIC : CLOCK_REALTIME;
-
 	if (env_parse_bool("WLR_DRM_NO_MODIFIERS")) {
 		wlr_log(WLR_DEBUG, "WLR_DRM_NO_MODIFIERS set, disabling modifiers");
 	} else {
-		ret = drmGetCap(drm->fd, DRM_CAP_ADDFB2_MODIFIERS, &cap);
+		int ret = drmGetCap(drm->fd, DRM_CAP_ADDFB2_MODIFIERS, &cap);
 		drm->addfb2_modifiers = ret == 0 && cap == 1;
 		wlr_log(WLR_DEBUG, "ADDFB2 modifiers %s",
 			drm->addfb2_modifiers ? "supported" : "unsupported");