drm/connector: demote connector force-probes for non-master clients

Force-probing a connector can be slow and cause flickering. As this
affects the global KMS state, let's make it so only the DRM master
can force-probe a connector.

Non-master DRM clients won't be able to force-probe a connector
anymore. Instead, KMS will perform a regular read-only connector
query.

Signed-off-by: Simon Ser <contact@emersion.fr>
Acked-by: Pekka Paalanen <pekka.paalanen@collabora.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20210402112212.5625-1-contact@emersion.fr

diff --git a/drivers/gpu/drm/drm_connector.c b/drivers/gpu/drm/drm_connector.c
index eab8c0b..9de1453 100644 (file)
--- a/drivers/gpu/drm/drm_connector.c
+++ b/drivers/gpu/drm/drm_connector.c
@@ -20,6 +20,7 @@
  * OF THIS SOFTWARE.
  */
 
+#include <drm/drm_auth.h>
 #include <drm/drm_connector.h>
 #include <drm/drm_edid.h>
 #include <drm/drm_encoder.h>
@@ -2376,9 +2377,13 @@ int drm_mode_getconnector(struct drm_device *dev, void *data,
 
        mutex_lock(&dev->mode_config.mutex);
        if (out_resp->count_modes == 0) {
-               connector->funcs->fill_modes(connector,
-                                            dev->mode_config.max_width,
-                                            dev->mode_config.max_height);
+               if (drm_is_current_master(file_priv))
+                       connector->funcs->fill_modes(connector,
+                                                    dev->mode_config.max_width,
+                                                    dev->mode_config.max_height);
+               else
+                       drm_dbg_kms(dev, "User-space requested a forced probe on [CONNECTOR:%d:%s] but is not the DRM master, demoting to read-only probe",
+                                   connector->base.id, connector->name);
        }
 
        out_resp->mm_width = connector->display_info.width_mm;

diff --git a/include/uapi/drm/drm_mode.h b/include/uapi/drm/drm_mode.h
index a5e76aa..9b6722d 100644 (file)
--- a/include/uapi/drm/drm_mode.h
+++ b/include/uapi/drm/drm_mode.h
@@ -413,9 +413,10 @@ enum drm_mode_subconnector {
  *
  * **Force-probing a connector**
  *
- * If the @count_modes field is set to zero, the kernel will perform a forced
- * probe on the connector to refresh the connector status, modes and EDID.
- * A forced-probe can be slow, might cause flickering and the ioctl will block.
+ * If the @count_modes field is set to zero and the DRM client is the current
+ * DRM master, the kernel will perform a forced probe on the connector to
+ * refresh the connector status, modes and EDID. A forced-probe can be slow,
+ * might cause flickering and the ioctl will block.
  *
  * User-space needs to force-probe connectors to ensure their metadata is
  * up-to-date at startup and after receiving a hot-plug event. User-space