drm_common: Add option to toggle use of atomic modesetting

It is useful when debugging to be able to force atomic off, or as a
workaround if atomic breaks for some user. Legacy modesetting is less
likely to break by virtue of being a less complex API.

DOCS/man/vo.rst

@@ -488,6 +488,16 @@ Available video output drivers are:
         Mode ID to use (resolution and frame rate).
         (default: 0)
 
+    ``--drm-atomic=<no|auto>``
+        Toggle use of atomic modesetting. Mostly useful for debugging.
+
+        :no:    Use legacy modesetting.
+        :auto:  Use atomic modesetting, falling back to legacy modesetting if
+                not available. (default)
+
+        Note: Only affects ``gpu-context=drm``. ``vo=drm`` supports legacy
+        modesetting only.
+
     ``--drm-draw-plane=<primary|overlay|N>``
         Select the DRM plane to which video and OSD is drawn to, under normal
         circumstances. The plane can be specified as ``primary``, which will

video/out/drm_common.c

@@ -48,6 +48,9 @@ const struct m_sub_options drm_conf = {
         OPT_STRING_VALIDATE("drm-connector", drm_connector_spec,
                             0, drm_validate_connector_opt),
         OPT_INT("drm-mode", drm_mode_id, 0),
+        OPT_CHOICE("drm-atomic", drm_atomic, 0,
+                   ({"no", 0},
+                    {"auto", 1})),
         OPT_CHOICE_OR_INT("drm-draw-plane", drm_draw_plane, 0, 0, INT_MAX,
                           ({"primary", DRM_OPTS_PRIMARY_PLANE},
                            {"overlay", DRM_OPTS_OVERLAY_PLANE})),
@@ -65,6 +68,7 @@ const struct m_sub_options drm_conf = {
         {0},
     },
     .defaults = &(const struct drm_opts) {
+        .drm_atomic = 1,
         .drm_draw_plane = DRM_OPTS_PRIMARY_PLANE,
         .drm_drmprime_video_plane = DRM_OPTS_OVERLAY_PLANE,
     },
@@ -276,9 +280,9 @@ static void parse_connector_spec(struct mp_log *log,
     }
 }
 
-
 struct kms *kms_create(struct mp_log *log, const char *connector_spec,
-                       int mode_id, int draw_plane, int drmprime_video_plane)
+                       int mode_id, int draw_plane, int drmprime_video_plane,
+                       bool use_atomic)
 {
     int card_no = -1;
     char *connector_name = NULL;
@@ -321,8 +325,10 @@ struct kms *kms_create(struct mp_log *log, const char *connector_spec,
         mp_err(log, "Failed to set Universal planes capability\n");
     }
 
-    if (drmSetClientCap(kms->fd, DRM_CLIENT_CAP_ATOMIC, 1)) {
+    if (!use_atomic) {
-        mp_verbose(log, "No DRM Atomic support found\n");
+        mp_verbose(log, "Using Legacy Modesetting\n");
+    } else if (drmSetClientCap(kms->fd, DRM_CLIENT_CAP_ATOMIC, 1)) {
+        mp_verbose(log, "No DRM Atomic support found. Falling back to legacy modesetting\n");
     } else {
         mp_verbose(log, "DRM Atomic support found\n");
         kms->atomic_context = drm_atomic_create_context(kms->log, kms->fd, kms->crtc_id,

video/out/drm_common.h

@@ -48,6 +48,7 @@ struct vt_switcher {
 struct drm_opts {
     char *drm_connector_spec;
     int drm_mode_id;
+    int drm_atomic;
     int drm_draw_plane;
     int drm_drmprime_video_plane;
     int drm_format;
@@ -65,7 +66,8 @@ void vt_switcher_release(struct vt_switcher *s, void (*handler)(void*),
                          void *user_data);
 
 struct kms *kms_create(struct mp_log *log, const char *connector_spec,
-                       int mode_id, int draw_plane, int drmprime_video_plane);
+                       int mode_id, int draw_plane, int drmprime_video_plane,
+                       bool use_atomic);
 void kms_destroy(struct kms *kms);
 double kms_get_display_fps(const struct kms *kms);
 

video/out/opengl/context_drm_egl.c

@@ -766,7 +766,8 @@ static bool drm_egl_init(struct ra_ctx *ctx)
     p->kms = kms_create(ctx->log, ctx->vo->opts->drm_opts->drm_connector_spec,
                         ctx->vo->opts->drm_opts->drm_mode_id,
                         ctx->vo->opts->drm_opts->drm_draw_plane,
-                        ctx->vo->opts->drm_opts->drm_drmprime_video_plane);
+                        ctx->vo->opts->drm_opts->drm_drmprime_video_plane,
+                        ctx->vo->opts->drm_opts->drm_atomic);
     if (!p->kms) {
         MP_ERR(ctx, "Failed to create KMS.\n");
         return false;

video/out/vo_drm.c

@@ -417,11 +417,10 @@ static int preinit(struct vo *vo)
         MP_WARN(vo, "Failed to set up VT switcher. Terminal switching will be unavailable.\n");
     }
 
-    p->kms = kms_create(
+    p->kms = kms_create(vo->log,
-        vo->log, vo->opts->drm_opts->drm_connector_spec,
+                        vo->opts->drm_opts->drm_connector_spec,
                         vo->opts->drm_opts->drm_mode_id,
-                 vo->opts->drm_opts->drm_draw_plane,
+                        0, 0, false);
-                 vo->opts->drm_opts->drm_drmprime_video_plane);
     if (!p->kms) {
         MP_ERR(vo, "Failed to create KMS.\n");
         goto err;