drm/i915/dp_mst: Improve BW sharing between MST streams

At the moment modesetting a stream CRTC will fail if the stream's BW
along with the current BW of all the other streams on the same MST link
is above the total BW of the MST link. Make the BW sharing more dynamic
by trying to reduce the link bpp of one or more streams on the MST link
in this case.

When selecting a stream to reduce the BW for, take into account which
link segment in the MST topology ran out of BW and which streams go
through this link segment. For instance with A,B,C streams in the same
MST topology A and B may share the BW of a link segment downstream of a
branch device, stream C not downstream of the branch device, hence not
affecting this BW. If this link segment's BW runs out one or both of
stream A/B's BW will be reduced until their total BW is within limits.

While reducing the link bpp for a given stream DSC may need to be
enabled for it, which requires FEC on the whole MST link. Check for this
condition and recompute the state for all streams taking the FEC
overhead into account (on 8b/10b links).

v2:
- Rebase on s/min_bpp_pipes/min_bpp_reached_pipes/ change.

Reviewed-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231030155843.2251023-29-imre.deak@intel.com

1 files changed, 129 insertions, 0 deletions

diff --git a/drivers/gpu/drm/i915/display/intel_dp_mst.c b/drivers/gpu/drm/i915/display/intel_dp_mst.c
index 079986b09f8b..b300e4b065df 100644
--- a/drivers/gpu/drm/i915/display/intel_dp_mst.c
+++ b/drivers/gpu/drm/i915/display/intel_dp_mst.c
@@ -43,6 +43,7 @@
 #include "intel_dpio_phy.h"
 #include "intel_hdcp.h"
 #include "intel_hotplug.h"
+#include "intel_link_bw.h"
 #include "intel_vdsc.h"
 #include "skl_scaler.h"
 
@@ -517,6 +518,10 @@ static int intel_dp_mst_compute_config(struct intel_encoder *encoder,
 	bool dsc_needed;
 	int ret = 0;
 
+	if (pipe_config->fec_enable &&
+	    !intel_dp_supports_fec(intel_dp, connector, pipe_config))
+		return -EINVAL;
+
 	if (adjusted_mode->flags & DRM_MODE_FLAG_DBLSCAN)
 		return -EINVAL;
 
@@ -636,6 +641,130 @@ intel_dp_mst_transcoder_mask(struct intel_atomic_state *state,
 	return transcoders;
 }
 
+static u8 get_pipes_downstream_of_mst_port(struct intel_atomic_state *state,
+					   struct drm_dp_mst_topology_mgr *mst_mgr,
+					   struct drm_dp_mst_port *parent_port)
+{
+	const struct intel_digital_connector_state *conn_state;
+	struct intel_connector *connector;
+	u8 mask = 0;
+	int i;
+
+	for_each_new_intel_connector_in_state(state, connector, conn_state, i) {
+		if (!conn_state->base.crtc)
+			continue;
+
+		if (&connector->mst_port->mst_mgr != mst_mgr)
+			continue;
+
+		if (connector->port != parent_port &&
+		    !drm_dp_mst_port_downstream_of_parent(mst_mgr,
+							  connector->port,
+							  parent_port))
+			continue;
+
+		mask |= BIT(to_intel_crtc(conn_state->base.crtc)->pipe);
+	}
+
+	return mask;
+}
+
+static int intel_dp_mst_check_fec_change(struct intel_atomic_state *state,
+					 struct drm_dp_mst_topology_mgr *mst_mgr,
+					 struct intel_link_bw_limits *limits)
+{
+	struct drm_i915_private *i915 = to_i915(state->base.dev);
+	struct intel_crtc *crtc;
+	u8 mst_pipe_mask;
+	u8 fec_pipe_mask = 0;
+	int ret;
+
+	mst_pipe_mask = get_pipes_downstream_of_mst_port(state, mst_mgr, NULL);
+
+	for_each_intel_crtc_in_pipe_mask(&i915->drm, crtc, mst_pipe_mask) {
+		struct intel_crtc_state *crtc_state =
+			intel_atomic_get_new_crtc_state(state, crtc);
+
+		/* Atomic connector check should've added all the MST CRTCs. */
+		if (drm_WARN_ON(&i915->drm, !crtc_state))
+			return -EINVAL;
+
+		if (crtc_state->fec_enable)
+			fec_pipe_mask |= BIT(crtc->pipe);
+	}
+
+	if (!fec_pipe_mask || mst_pipe_mask == fec_pipe_mask)
+		return 0;
+
+	limits->force_fec_pipes |= mst_pipe_mask;
+
+	ret = intel_modeset_pipes_in_mask_early(state, "MST FEC",
+						mst_pipe_mask);
+
+	return ret ? : -EAGAIN;
+}
+
+static int intel_dp_mst_check_bw(struct intel_atomic_state *state,
+				 struct drm_dp_mst_topology_mgr *mst_mgr,
+				 struct drm_dp_mst_topology_state *mst_state,
+				 struct intel_link_bw_limits *limits)
+{
+	struct drm_dp_mst_port *mst_port;
+	u8 mst_port_pipes;
+	int ret;
+
+	ret = drm_dp_mst_atomic_check_mgr(&state->base, mst_mgr, mst_state, &mst_port);
+	if (ret != -ENOSPC)
+		return ret;
+
+	mst_port_pipes = get_pipes_downstream_of_mst_port(state, mst_mgr, mst_port);
+
+	ret = intel_link_bw_reduce_bpp(state, limits,
+				       mst_port_pipes, "MST link BW");
+
+	return ret ? : -EAGAIN;
+}
+
+/**
+ * intel_dp_mst_atomic_check_link - check all modeset MST link configuration
+ * @state: intel atomic state
+ * @limits: link BW limits
+ *
+ * Check the link configuration for all modeset MST outputs. If the
+ * configuration is invalid @limits will be updated if possible to
+ * reduce the total BW, after which the configuration for all CRTCs in
+ * @state must be recomputed with the updated @limits.
+ *
+ * Returns:
+ *   - 0 if the confugration is valid
+ *   - %-EAGAIN, if the configuration is invalid and @limits got updated
+ *     with fallback values with which the configuration of all CRTCs in
+ *     @state must be recomputed
+ *   - Other negative error, if the configuration is invalid without a
+ *     fallback possibility, or the check failed for another reason
+ */
+int intel_dp_mst_atomic_check_link(struct intel_atomic_state *state,
+				   struct intel_link_bw_limits *limits)
+{
+	struct drm_dp_mst_topology_mgr *mgr;
+	struct drm_dp_mst_topology_state *mst_state;
+	int ret;
+	int i;
+
+	for_each_new_mst_mgr_in_state(&state->base, mgr, mst_state, i) {
+		ret = intel_dp_mst_check_fec_change(state, mgr, limits);
+		if (ret)
+			return ret;
+
+		ret = intel_dp_mst_check_bw(state, mgr, mst_state,
+					    limits);
+		if (ret)
+			return ret;
+	}
+
+	return 0;
+}
+
 static int intel_dp_mst_compute_config_late(struct intel_encoder *encoder,
 					    struct intel_crtc_state *crtc_state,
 					    struct drm_connector_state *conn_state)