drm/i915/dp_mst: Add atomic state for all streams on pre-tgl platforms

If an MST stream is modeset, its state must be checked along all the
other streams on the same MST link, for instance to resolve a BW
overallocation of a non-sink MST port or to make sure that the FEC is
enabled/disabled the same way for all these streams.

To prepare for that this patch adds all the stream CRTCs to the atomic
state and marks them for modeset similarly to tgl+ platforms. (If the
state computation doesn't change the state the CRTC is switched back to
fastset mode.)

So far on tgl+ this was required because all streams in the topology
shared the master transcoder. For older platforms this didn't apply but
adding all the state is required now on all platforms based on the
above.

v2:
- Add code and commit log comment clarifying the requirements on old/new
  platforms. (Stan)
- Rename the function based on the new semantic. (Ville)

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231030155843.2251023-15-imre.deak@intel.com

drivers/gpu/drm/i915/display/intel_dp_mst.c

@@ -563,19 +563,23 @@ static int intel_dp_mst_compute_config_late(struct intel_encoder *encoder,
  * that shares the same MST stream as mode changed,
  * intel_modeset_pipe_config()+intel_crtc_check_fastset() will take care to do
  * a fastset when possible.
+ *
+ * On TGL+ this is required since each stream go through a master transcoder,
+ * so if the master transcoder needs modeset, all other streams in the
+ * topology need a modeset. All platforms need to add the atomic state
+ * for all streams in the topology, since a modeset on one may require
+ * changing the MST link BW usage of the others, which in turn needs a
+ * recomputation of the corresponding CRTC states.
  */
 static int
-intel_dp_mst_atomic_master_trans_check(struct intel_connector *connector,
-				       struct intel_atomic_state *state)
+intel_dp_mst_atomic_topology_check(struct intel_connector *connector,
+				   struct intel_atomic_state *state)
 {
 	struct drm_i915_private *dev_priv = to_i915(state->base.dev);
 	struct drm_connector_list_iter connector_list_iter;
 	struct intel_connector *connector_iter;
 	int ret = 0;
 
-	if (DISPLAY_VER(dev_priv) < 12)
-		return  0;
-
 	if (!intel_connector_needs_modeset(state, &connector->base))
 		return 0;
 
@@ -629,7 +633,7 @@ intel_dp_mst_atomic_check(struct drm_connector *connector,
 	if (ret)
 		return ret;
 
-	ret = intel_dp_mst_atomic_master_trans_check(intel_connector, state);
+	ret = intel_dp_mst_atomic_topology_check(intel_connector, state);
 	if (ret)
 		return ret;