drm: Detect if drivers support buffer modifiers

Use drmGetCap() in the DRM modesetting renderer to detect whether
framebuffers can be created with modifiers, instead of always trying
to use them and falling back to avoid them.

platform/drm/cog-drm-modeset-renderer.c

@@ -99,6 +99,7 @@ typedef struct {
     drmModeModeInfo mode;
     bool            mode_set;
     bool            atomic_modesetting;
+    bool            addfb2_modifiers;
 
     struct {
         drmModeObjectProperties *props;
@@ -190,14 +191,13 @@ drm_create_buffer_for_bo(CogDrmModesetRenderer *self,
         in_modifiers[i] = in_modifiers[0];
     }
 
-    int flags = 0;
-    if (in_modifiers[0])
-        flags = DRM_MODE_FB_MODIFIERS;
-
+    int      ret;
     uint32_t fb_id = 0;
-    int ret = drmModeAddFB2WithModifiers(get_drm_fd(self), width, height, format, in_handles, in_strides, in_offsets,
-                                         in_modifiers, &fb_id, flags);
-    if (ret) {
+
+    if (G_LIKELY(self->addfb2_modifiers)) {
+        ret = drmModeAddFB2WithModifiers(get_drm_fd(self), width, height, format, in_handles, in_strides, in_offsets,
+                                         in_modifiers, &fb_id, DRM_MODE_FB_MODIFIERS);
+    } else {
         in_handles[0] = gbm_bo_get_handle(bo).u32;
         in_handles[1] = in_handles[2] = in_handles[3] = 0;
         in_strides[0] = gbm_bo_get_stride(bo);
@@ -661,6 +661,15 @@ cog_drm_modeset_renderer_new(struct gbm_device     *gbm_dev,
         .plane_id = plane_id,
         .atomic_modesetting = atomic_modesetting,
     };
+
+    uint64_t value = 0;
+    if (drmGetCap(gbm_device_get_fd(self->gbm_dev), DRM_CAP_ADDFB2_MODIFIERS, &value)) {
+        g_debug("%s: Cannot get addfb2_modifiers capability: %s", G_STRFUNC, g_strerror(errno));
+    } else {
+        g_debug("%s: Capability addfb2_modifiers = %#" PRIx64, G_STRFUNC, value);
+        self->addfb2_modifiers = !!value;
+    }
+
     wl_list_init(&self->buffer_list);
     memcpy(&self->mode, mode, sizeof(drmModeModeInfo));
 

platform/drm/cog-platform-drm.c

@@ -131,6 +131,7 @@ static struct {
     double   device_scale;
 
     bool atomic_modesetting;
+    bool addfb2_modifiers;
     bool mode_set;
 } drm_data = {
     .fd = -1,