drm/probe_helper: Add drm_connector_helper_funcs.mode_valid_ctx

This is just an atomic version of mode_valid, which is intended to be
used for situations where a driver might need to check the atomic state
of objects other than the connector itself. One such example is with
MST, where the maximum possible bandwidth on a connector can change
dynamically irregardless of the display configuration.

Changes since v1:
* Use new drm logging functions
* Make some corrections in the mode_valid_ctx kdoc
* Return error codes or 0 from ->mode_valid_ctx() on fail, and store the
  drm_mode_status in an additional function parameter
Changes since v2:
* Don't accidentally assign ret to mode->status on success, or we'll
  squash legitimate mode validation results
* Don't forget to assign MODE_OK to status in drm_connector_mode_valid()
  if we have no callbacks
* Drop leftover hunk in drm_modes.h around enum drm_mode_status
Changes since v3:
* s/return ret/return 0/ in drm_mode_validate_pipeline()
* Minor cleanup in drm_connector_mode_valid()

Tested-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Imre Deak <imre.deak@intel.com>
Cc: Lee Shawn C <shawn.c.lee@intel.com>
Signed-off-by: Lyude Paul <lyude@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200713170746.254388-2-lyude@redhat.com

1 files changed, 42 insertions, 0 deletions

diff --git a/include/drm/drm_modeset_helper_vtables.h b/include/drm/drm_modeset_helper_vtables.h
index 421a30f08463..4efec30f8bad 100644
--- a/include/drm/drm_modeset_helper_vtables.h
+++ b/include/drm/drm_modeset_helper_vtables.h
@@ -968,6 +968,48 @@ struct drm_connector_helper_funcs {
 	 */
 	enum drm_mode_status (*mode_valid)(struct drm_connector *connector,
 					   struct drm_display_mode *mode);
+
+	/**
+	 * @mode_valid_ctx:
+	 *
+	 * Callback to validate a mode for a connector, irrespective of the
+	 * specific display configuration.
+	 *
+	 * This callback is used by the probe helpers to filter the mode list
+	 * (which is usually derived from the EDID data block from the sink).
+	 * See e.g. drm_helper_probe_single_connector_modes().
+	 *
+	 * This function is optional, and is the atomic version of
+	 * &drm_connector_helper_funcs.mode_valid.
+	 *
+	 * To allow for accessing the atomic state of modesetting objects, the
+	 * helper libraries always call this with ctx set to a valid context,
+	 * and &drm_mode_config.connection_mutex will always be locked with
+	 * the ctx parameter set to @ctx. This allows for taking additional
+	 * locks as required.
+	 *
+	 * Even though additional locks may be acquired, this callback is
+	 * still expected not to take any constraints into account which would
+	 * be influenced by the currently set display state - such constraints
+	 * should be handled in the driver's atomic check. For example, if a
+	 * connector shares display bandwidth with other connectors then it
+	 * would be ok to validate the minimum bandwidth requirement of a mode
+	 * against the maximum possible bandwidth of the connector. But it
+	 * wouldn't be ok to take the current bandwidth usage of other
+	 * connectors into account, as this would change depending on the
+	 * display state.
+	 *
+	 * Returns:
+	 * 0 if &drm_connector_helper_funcs.mode_valid_ctx succeeded and wrote
+	 * the &enum drm_mode_status value to @status, or a negative error
+	 * code otherwise.
+	 *
+	 */
+	int (*mode_valid_ctx)(struct drm_connector *connector,
+			      struct drm_display_mode *mode,
+			      struct drm_modeset_acquire_ctx *ctx,
+			      enum drm_mode_status *status);
+
 	/**
 	 * @best_encoder:
 	 *