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.

backend/backend.c

@@ -116,13 +116,6 @@ static struct wlr_session *session_create_and_wait(struct wl_display *disp) {
 #endif
 }
 
-clockid_t wlr_backend_get_presentation_clock(struct wlr_backend *backend) {
-	if (backend->impl->get_presentation_clock) {
-		return backend->impl->get_presentation_clock(backend);
-	}
-	return CLOCK_MONOTONIC;
-}
-
 int wlr_backend_get_drm_fd(struct wlr_backend *backend) {
 	if (!backend->impl->get_drm_fd) {
 		return -1;

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,
 };

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");

backend/multi/backend.c

@@ -63,20 +63,6 @@ static void multi_backend_destroy(struct wlr_backend *wlr_backend) {
 	free(backend);
 }
 
-static clockid_t multi_backend_get_presentation_clock(
-		struct wlr_backend *backend) {
-	struct wlr_multi_backend *multi = multi_backend_from_backend(backend);
-
-	struct subbackend_state *sub;
-	wl_list_for_each(sub, &multi->backends, link) {
-		if (sub->backend->impl->get_presentation_clock) {
-			return wlr_backend_get_presentation_clock(sub->backend);
-		}
-	}
-
-	return CLOCK_MONOTONIC;
-}
-
 static int multi_backend_get_drm_fd(struct wlr_backend *backend) {
 	struct wlr_multi_backend *multi = multi_backend_from_backend(backend);
 
@@ -115,7 +101,6 @@ static uint32_t multi_backend_get_buffer_caps(struct wlr_backend *backend) {
 static const struct wlr_backend_impl backend_impl = {
 	.start = multi_backend_start,
 	.destroy = multi_backend_destroy,
-	.get_presentation_clock = multi_backend_get_presentation_clock,
 	.get_drm_fd = multi_backend_get_drm_fd,
 	.get_buffer_caps = multi_backend_get_buffer_caps,
 };

backend/wayland/backend.c

@@ -95,7 +95,11 @@ static const struct xdg_wm_base_listener xdg_wm_base_listener = {
 static void presentation_handle_clock_id(void *data,
 		struct wp_presentation *presentation, uint32_t clock) {
 	struct wlr_wl_backend *wl = data;
-	wl->presentation_clock = clock;
+
+	if (clock != CLOCK_MONOTONIC) {
+		wp_presentation_destroy(wl->presentation);
+		wl->presentation = NULL;
+	}
 }
 
 static const struct wp_presentation_listener presentation_listener = {
@@ -535,11 +539,6 @@ static void backend_destroy(struct wlr_backend *backend) {
 	free(wl);
 }
 
-static clockid_t backend_get_presentation_clock(struct wlr_backend *backend) {
-	struct wlr_wl_backend *wl = get_wl_backend_from_backend(backend);
-	return wl->presentation_clock;
-}
-
 static int backend_get_drm_fd(struct wlr_backend *backend) {
 	struct wlr_wl_backend *wl = get_wl_backend_from_backend(backend);
 	return wl->drm_fd;
@@ -554,7 +553,6 @@ static uint32_t 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 = get_buffer_caps,
 };
@@ -585,7 +583,6 @@ struct wlr_backend *wlr_wl_backend_create(struct wl_display *display,
 	wl_list_init(&wl->outputs);
 	wl_list_init(&wl->seats);
 	wl_list_init(&wl->buffers);
-	wl->presentation_clock = CLOCK_MONOTONIC;
 
 	if (remote_display != NULL) {
 		wl->remote_display = remote_display;

include/backend/drm/drm.h

@@ -4,7 +4,6 @@
 #include <stdbool.h>
 #include <stddef.h>
 #include <stdint.h>
-#include <time.h>
 #include <wayland-server-core.h>
 #include <wayland-util.h>
 #include <wlr/backend/drm.h>
@@ -79,7 +78,6 @@ struct wlr_drm_backend {
 
 	struct wlr_drm_backend *parent;
 	const struct wlr_drm_interface *iface;
-	clockid_t clock;
 	bool addfb2_modifiers;
 
 	int fd;

include/backend/wayland.h

@@ -43,7 +43,6 @@ struct wlr_wl_backend {
 	struct zwp_relative_pointer_manager_v1 *zwp_relative_pointer_manager_v1;
 	struct wl_list seats; // wlr_wl_seat.link
 	struct zwp_tablet_manager_v2 *tablet_manager;
-	clockid_t presentation_clock;
 	struct wlr_drm_format_set shm_formats;
 	struct wlr_drm_format_set linux_dmabuf_v1_formats;
 	struct wl_drm *legacy_drm;

include/wlr/backend.h

@@ -51,10 +51,6 @@ bool wlr_backend_start(struct wlr_backend *backend);
  * automatically when the struct wl_display is destroyed.
  */
 void wlr_backend_destroy(struct wlr_backend *backend);
-/**
- * Returns the clock used by the backend for presentation feedback.
- */
-clockid_t wlr_backend_get_presentation_clock(struct wlr_backend *backend);
 /**
  * Returns the DRM node file descriptor used by the backend's underlying
  * platform. Can be used by consumers for additional rendering operations.

include/wlr/backend/interface.h

@@ -10,13 +10,11 @@
 #define WLR_BACKEND_INTERFACE_H
 
 #include <stdbool.h>
-#include <time.h>
 #include <wlr/backend.h>
 
 struct wlr_backend_impl {
 	bool (*start)(struct wlr_backend *backend);
 	void (*destroy)(struct wlr_backend *backend);
-	clockid_t (*get_presentation_clock)(struct wlr_backend *backend);
 	int (*get_drm_fd)(struct wlr_backend *backend);
 	uint32_t (*get_buffer_caps)(struct wlr_backend *backend);
 };

include/wlr/types/wlr_presentation_time.h

@@ -21,7 +21,6 @@ struct wlr_output_event_present;
 
 struct wlr_presentation {
 	struct wl_global *global;
-	clockid_t clock;
 
 	struct {
 		struct wl_signal destroy;

types/output/output.c

@@ -913,9 +913,7 @@ void wlr_output_send_present(struct wlr_output *output,
 
 	struct timespec now;
 	if (event->presented && event->when == NULL) {
-		clockid_t clock = wlr_backend_get_presentation_clock(output->backend);
+		if (clock_gettime(CLOCK_MONOTONIC, &now) != 0) {
-		errno = 0;
-		if (clock_gettime(clock, &now) != 0) {
 			wlr_log_errno(WLR_ERROR, "failed to send output present event: "
 				"failed to read clock");
 			return;

types/wlr_presentation_time.c

@@ -168,7 +168,7 @@ static void presentation_bind(struct wl_client *client, void *data,
 	wl_resource_set_implementation(resource, &presentation_impl, presentation,
 		NULL);
 
-	wp_presentation_send_clock_id(resource, (uint32_t)presentation->clock);
+	wp_presentation_send_clock_id(resource, CLOCK_MONOTONIC);
 }
 
 static void handle_display_destroy(struct wl_listener *listener, void *data) {
@@ -194,8 +194,6 @@ struct wlr_presentation *wlr_presentation_create(struct wl_display *display,
 		return NULL;
 	}
 
-	presentation->clock = wlr_backend_get_presentation_clock(backend);
-
 	wl_signal_init(&presentation->events.destroy);
 
 	presentation->display_destroy.notify = handle_display_destroy;