drm/i915/dp_mst: Enable MST DSC decompression for all streams

Enable DSC decompression for all streams. In particular atm if a sink is
connected to a last branch device that is downstream of the first branch
device connected to the source, decompression is not enabled for it.
Similarly it's not enabled if the sink supports this with the last
branch device passing through the compressed stream to it.

Enable DSC in the above cases as well. Since last branch devices may
handle the decompression for multiple ports, toggling DSC needs to be
refcounted, add this using the DSC AUX device as a reference.

v2:
- Fix refcounting, setting/clearing
  connector->dp.dsc_decompression_enabled always as needed. (Stan)
- Make the refcounting more uniform for the SST vs. MST case.
- Add state checks for connector->dp.dsc_decompression_enabled and
  connector crtc.
- Sanitize connector DSC decompression state during HW setup.
- s/use_count/ref_count/
v3:
- Remove stale TODO: comment to set the actual decompression_aux.

Cc: Stanislav Lisovskiy <stanislav.lisovskiy@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/20231107001505.3370108-6-imre.deak@intel.com

drivers/gpu/drm/i915/display/intel_display_types.h

@@ -626,6 +626,7 @@ struct intel_connector {
 		u8 fec_capability;
 
 		u8 dsc_hblank_expansion_quirk:1;
+		u8 dsc_decompression_enabled:1;
 	} dp;
 
 	/* Work struct to schedule a uevent on link train failure */

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

@@ -1403,6 +1403,7 @@ static bool intel_dp_supports_dsc(const struct intel_connector *connector,
 		return false;
 
 	return intel_dsc_source_support(crtc_state) &&
+		connector->dp.dsc_decompression_aux &&
 		drm_dp_sink_supports_dsc(connector->dp.dsc_dpcd);
 }
 
@@ -2986,6 +2987,65 @@ intel_dp_sink_set_dsc_passthrough(const struct intel_connector *connector,
 			    str_enable_disable(enable));
 }
 
+static int intel_dp_dsc_aux_ref_count(struct intel_atomic_state *state,
+				      const struct intel_connector *connector,
+				      bool for_get_ref)
+{
+	struct drm_i915_private *i915 = to_i915(state->base.dev);
+	struct drm_connector *_connector_iter;
+	struct drm_connector_state *old_conn_state;
+	struct drm_connector_state *new_conn_state;
+	int ref_count = 0;
+	int i;
+
+	/*
+	 * On SST the decompression AUX device won't be shared, each connector
+	 * uses for this its own AUX targeting the sink device.
+	 */
+	if (!connector->mst_port)
+		return connector->dp.dsc_decompression_enabled ? 1 : 0;
+
+	for_each_oldnew_connector_in_state(&state->base, _connector_iter,
+					   old_conn_state, new_conn_state, i) {
+		const struct intel_connector *
+			connector_iter = to_intel_connector(_connector_iter);
+
+		if (connector_iter->mst_port != connector->mst_port)
+			continue;
+
+		if (!connector_iter->dp.dsc_decompression_enabled)
+			continue;
+
+		drm_WARN_ON(&i915->drm,
+			    (for_get_ref && !new_conn_state->crtc) ||
+			    (!for_get_ref && !old_conn_state->crtc));
+
+		if (connector_iter->dp.dsc_decompression_aux ==
+		    connector->dp.dsc_decompression_aux)
+			ref_count++;
+	}
+
+	return ref_count;
+}
+
+static bool intel_dp_dsc_aux_get_ref(struct intel_atomic_state *state,
+				     struct intel_connector *connector)
+{
+	bool ret = intel_dp_dsc_aux_ref_count(state, connector, true) == 0;
+
+	connector->dp.dsc_decompression_enabled = true;
+
+	return ret;
+}
+
+static bool intel_dp_dsc_aux_put_ref(struct intel_atomic_state *state,
+				     struct intel_connector *connector)
+{
+	connector->dp.dsc_decompression_enabled = false;
+
+	return intel_dp_dsc_aux_ref_count(state, connector, false) == 0;
+}
+
 /**
  * intel_dp_sink_enable_decompression - Enable DSC decompression in sink/last branch device
  * @state: atomic state
@@ -3009,7 +3069,11 @@ void intel_dp_sink_enable_decompression(struct intel_atomic_state *state,
 		return;
 
 	if (drm_WARN_ON(&i915->drm,
-			!connector->dp.dsc_decompression_aux))
+			!connector->dp.dsc_decompression_aux ||
+			connector->dp.dsc_decompression_enabled))
+		return;
+
+	if (!intel_dp_dsc_aux_get_ref(state, connector))
 		return;
 
 	intel_dp_sink_set_dsc_passthrough(connector, true);
@@ -3036,7 +3100,11 @@ void intel_dp_sink_disable_decompression(struct intel_atomic_state *state,
 		return;
 
 	if (drm_WARN_ON(&i915->drm,
-			!connector->dp.dsc_decompression_aux))
+			!connector->dp.dsc_decompression_aux ||
+			!connector->dp.dsc_decompression_enabled))
+		return;
+
+	if (!intel_dp_dsc_aux_put_ref(state, connector))
 		return;
 
 	intel_dp_sink_set_dsc_decompression(connector, false);

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

@@ -777,12 +777,7 @@ static void intel_mst_disable_dp(struct intel_atomic_state *state,
 
 	intel_audio_codec_disable(encoder, old_crtc_state, old_conn_state);
 
-	if (intel_dp->active_mst_links == 1) /* last stream ? */
-		/*
-		 * TODO: disable decompression for all streams/in any MST ports, not
-		 * only in the first downstream branch device.
-		 */
-		intel_dp_sink_disable_decompression(state, connector, old_crtc_state);
+	intel_dp_sink_disable_decompression(state, connector, old_crtc_state);
 }
 
 static void intel_mst_post_disable_dp(struct intel_atomic_state *state,
@@ -939,15 +934,11 @@ static void intel_mst_pre_enable_dp(struct intel_atomic_state *state,
 
 	drm_dp_send_power_updown_phy(&intel_dp->mst_mgr, connector->port, true);
 
-	if (first_mst_stream) {
-		/*
-		 * TODO: enable decompression for all streams/in any MST ports, not
-		 * only in the first downstream branch device.
-		 */
-		intel_dp_sink_enable_decompression(state, connector, pipe_config);
+	intel_dp_sink_enable_decompression(state, connector, pipe_config);
+
+	if (first_mst_stream)
 		dig_port->base.pre_enable(state, &dig_port->base,
 						pipe_config, NULL);
-	}
 
 	intel_dp->active_mst_links++;
 
@@ -1394,12 +1385,7 @@ static struct drm_connector *intel_dp_add_mst_connector(struct drm_dp_mst_topolo
 	intel_connector->port = port;
 	drm_dp_mst_get_port_malloc(port);
 
-	/*
-	 * TODO: set the AUX for the actual MST port decompressing the stream.
-	 * At the moment the driver only supports enabling this globally in the
-	 * first downstream MST branch, via intel_dp's (root port) AUX.
-	 */
-	intel_connector->dp.dsc_decompression_aux = &intel_dp->aux;
+	intel_connector->dp.dsc_decompression_aux = drm_dp_mst_dsc_aux_for_port(port);
 	intel_dp_mst_read_decompression_port_dsc_caps(intel_dp, intel_connector);
 	intel_connector->dp.dsc_hblank_expansion_quirk =
 		detect_dsc_hblank_expansion_quirk(intel_connector);

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

@@ -318,6 +318,12 @@ static void intel_modeset_update_connector_atomic_state(struct drm_i915_private
 			const struct intel_crtc_state *crtc_state =
 				to_intel_crtc_state(crtc->base.state);
 
+			if (crtc_state->dsc.compression_enable) {
+				drm_WARN_ON(&i915->drm, !connector->dp.dsc_decompression_aux);
+				connector->dp.dsc_decompression_enabled = true;
+			} else {
+				connector->dp.dsc_decompression_enabled = false;
+			}
 			conn_state->max_bpc = (crtc_state->pipe_bpp ?: 24) / 3;
 		}
 	}