drm: Document drm_connector_helper_funcs

Nothing special, except the somewhat awkward split in probe helper
callbacks between here and drm_crtc_funcs.

v2: Suggestions from Thierry.

Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1449218769-16577-25-git-send-email-daniel.vetter@ffwll.ch
Reviewed-by: Thierry Reding <treding@nvidia.com>

1 files changed, 101 insertions, 5 deletions

diff --git a/include/drm/drm_modeset_helper_vtables.h b/include/drm/drm_modeset_helper_vtables.h
index c77b7dcf343b..4b3869bd49b5 100644
--- a/include/drm/drm_modeset_helper_vtables.h
+++ b/include/drm/drm_modeset_helper_vtables.h
@@ -270,18 +270,114 @@ static inline void drm_encoder_helper_add(struct drm_encoder *encoder,
 
 /**
  * struct drm_connector_helper_funcs - helper operations for connectors
- * @get_modes: get mode list for this connector
- * @mode_valid: is this mode valid on the given connector? (optional)
- * @best_encoder: return the preferred encoder for this connector
- * @atomic_best_encoder: atomic version of @best_encoder
  *
- * The helper operations are called by the mid-layer CRTC helper.
+ * These functions are used by the atomic and legacy modeset helpers and by the
+ * probe helpers.
  */
 struct drm_connector_helper_funcs {
+        /**
+         * @get_modes:
+         *
+         * This function should fill in all modes currently valid for the sink
+         * into the connector->probed_modes list. It should also update the
+         * EDID property by calling drm_mode_connector_update_edid_property().
+         *
+         * The usual way to implement this is to cache the EDID retrieved in the
+         * probe callback somewhere in the driver-private connector structure.
+         * In this function drivers then parse the modes in the EDID and add
+         * them by calling drm_add_edid_modes(). But connectors that driver a
+         * fixed panel can also manually add specific modes using
+         * drm_mode_probed_add(). Finally drivers that support audio probably
+         * want to update the ELD data, too, using drm_edid_to_eld().
+         *
+         * This function is only called after the ->detect() hook has indicated
+         * that a sink is connected and when the EDID isn't overridden through
+         * sysfs or the kernel commandline.
+         *
+         * This callback is used by the probe helpers in e.g.
+         * drm_helper_probe_single_connector_modes().
+         *
+         * RETURNS:
+         *
+         * The number of modes added by calling drm_mode_probed_add().
+         */
         int (*get_modes)(struct drm_connector *connector);
+
+        /**
+         * @mode_valid:
+         *
+         * 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().
+         *
+         * NOTE:
+         *
+         * This only filters the mode list supplied to userspace in the
+         * GETCONNECOTR IOCTL. Userspace is free to create modes of its own and
+         * ask the kernel to use them. It this case the atomic helpers or legacy
+         * CRTC helpers will not call this function. Drivers therefore must
+         * still fully validate any mode passed in in a modeset request.
+         *
+         * RETURNS:
+         *
+         * Either MODE_OK or one of the failure reasons in enum
+         * &drm_mode_status.
+         */
         enum drm_mode_status (*mode_valid)(struct drm_connector *connector,
                                            struct drm_display_mode *mode);
+        /**
+         * @best_encoder:
+         *
+         * This function should select the best encoder for the given connector.
+         *
+         * This function is used by both the atomic helpers (in the
+         * drm_atomic_helper_check_modeset() function) and in the legacy CRTC
+         * helpers.
+         *
+         * NOTE:
+         *
+         * In atomic drivers this function is called in the check phase of an
+         * atomic update. The driver is not allowed to change or inspect
+         * anything outside of arguments passed-in. Atomic drivers which need to
+         * inspect dynamic configuration state should instead use
+         * @atomic_best_encoder.
+         *
+         * RETURNS:
+         *
+         * Encoder that should be used for the given connector and connector
+         * state, or NULL if no suitable encoder exists. Note that the helpers
+         * will ensure that encoders aren't used twice, drivers should not check
+         * for this.
+         */
         struct drm_encoder *(*best_encoder)(struct drm_connector *connector);
+
+        /**
+         * @atomic_best_encoder:
+         *
+         * This is the atomic version of @best_encoder for atomic drivers which
+         * need to select the best encoder depending upon the desired
+         * configuration and can't select it statically.
+         *
+         * This function is used by drm_atomic_helper_check_modeset() and either
+         * this or @best_encoder is required.
+         *
+         * NOTE:
+         *
+         * This function is called in the check phase of an atomic update. The
+         * driver is not allowed to change anything outside of the free-standing
+         * state objects passed-in or assembled in the overall &drm_atomic_state
+         * update tracking structure.
+         *
+         * RETURNS:
+         *
+         * Encoder that should be used for the given connector and connector
+         * state, or NULL if no suitable encoder exists. Note that the helpers
+         * will ensure that encoders aren't used twice, drivers should not check
+         * for this.
+         */
         struct drm_encoder *(*atomic_best_encoder)(struct drm_connector *connector,
                                                    struct drm_connector_state *connector_state);
 };