[PATCH 3/3] drm/dp/mst: Track available time slots in DP Multi-Stream Transport Packet

[Dhinakaran Pandiyan]

The avail_slots member in struct drm_dp_mst_topology_mgr does not really
track the available time slots in a MTP(Multi-Stream Transport Packet). It
is assigned an initial value when the topology manager is setup but not
updated after that.

So, let's use avail_slots to store the number of unallocated slots out of
the total 64. The value will be updated when vcpi allocation or reset
happens. Since vcpi allocation and deallocation can happen simultaneously,
the struct drm_dp_mst_topology_mgr.lock mutex is used to protect
it from concurrent accesses.

Signed-off-by: Dhinakaran Pandiyan <dhinakaran.pandiyan at intel.com>
---
 drivers/gpu/drm/drm_dp_mst_topology.c | 55 ++++++++++++++++++++++++++---------
 drivers/gpu/drm/i915/intel_dp_mst.c   |  5 +++-
 include/drm/drm_dp_mst_helper.h       |  2 +-
 3 files changed, 47 insertions(+), 15 deletions(-)

diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c
index 26dfd99..19e2250 100644
--- a/drivers/gpu/drm/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/drm_dp_mst_topology.c
@@ -2040,7 +2040,9 @@ int drm_dp_mst_topology_mgr_set_mst(struct drm_dp_mst_topology_mgr *mgr, bool ms
 		}
 		mgr->total_pbn = 64 * mgr->pbn_div;
 		mgr->total_slots = 64;
-		mgr->avail_slots = mgr->total_slots;
+
+		/* 1 slot out of the 64 time slots is used for MTP header */
+		mgr->avail_slots = mgr->total_slots - 1;
 
 		/* add initial branch device at LCT 1 */
 		mstb = drm_dp_add_mst_branch_device(1, NULL);
@@ -2465,34 +2467,52 @@ EXPORT_SYMBOL(drm_dp_mst_get_edid);
  * @pbn: payload bandwidth to convert into slots.
  */
 int drm_dp_find_vcpi_slots(struct drm_dp_mst_topology_mgr *mgr,
-			   int pbn)
+			   struct drm_dp_mst_port *port, int pbn)
 {
-	int num_slots;
+	int req_slots, curr_slots, new_slots, ret;
+
+	req_slots = DIV_ROUND_UP(pbn, mgr->pbn_div);
+	curr_slots = drm_dp_mst_get_vcpi_slots(mgr, port);
 
-	num_slots = DIV_ROUND_UP(pbn, mgr->pbn_div);
+	if (req_slots <= curr_slots)
+		return req_slots;
 
-	if (num_slots > mgr->avail_slots)
-		return -ENOSPC;
-	return num_slots;
+	new_slots = req_slots - curr_slots;
+	mutex_lock(&mgr->lock);
+	if (new_slots <= mgr->avail_slots) {
+		ret = req_slots;
+	} else {
+		DRM_DEBUG_KMS("not enough vcpi slots, req=%d avail=%d\n", req_slots, mgr->avail_slots);
+		ret =  -ENOSPC;
+	}
+	mutex_unlock(&mgr->lock);
+
+	return ret;
 }
 EXPORT_SYMBOL(drm_dp_find_vcpi_slots);
 
 static int drm_dp_init_vcpi(struct drm_dp_mst_topology_mgr *mgr,
 			    struct drm_dp_vcpi *vcpi, int pbn)
 {
-	int num_slots;
+	int req_slots;
 	int ret;
 
-	num_slots = DIV_ROUND_UP(pbn, mgr->pbn_div);
+	req_slots = DIV_ROUND_UP(pbn, mgr->pbn_div);
 
-	if (num_slots > mgr->avail_slots)
-		return -ENOSPC;
+	mutex_lock(&mgr->lock);
+	if (req_slots > mgr->avail_slots) {
+		ret = -ENOSPC;
+		goto out;
+	}
 
 	vcpi->pbn = pbn;
-	vcpi->aligned_pbn = num_slots * mgr->pbn_div;
-	vcpi->num_slots = num_slots;
+	vcpi->aligned_pbn = req_slots * mgr->pbn_div;
+	vcpi->num_slots = req_slots;
 
 	ret = drm_dp_mst_assign_payload_id(mgr, vcpi);
+
+out:
+	mutex_unlock(&mgr->lock);
 	if (ret < 0)
 		return ret;
 	return 0;
@@ -2530,6 +2550,10 @@ bool drm_dp_mst_allocate_vcpi(struct drm_dp_mst_topology_mgr *mgr, struct drm_dp
 	DRM_DEBUG_KMS("initing vcpi for %d %d\n", pbn, port->vcpi.num_slots);
 	*slots = port->vcpi.num_slots;
 
+	mutex_lock(&mgr->lock);
+	mgr->avail_slots -= port->vcpi.num_slots;
+	mutex_unlock(&mgr->lock);
+
 	drm_dp_put_port(port);
 	return true;
 out:
@@ -2562,6 +2586,11 @@ void drm_dp_mst_reset_vcpi_slots(struct drm_dp_mst_topology_mgr *mgr, struct drm
 	port = drm_dp_get_validated_port_ref(mgr, port);
 	if (!port)
 		return;
+
+	mutex_lock(&mgr->lock);
+	mgr->avail_slots += port->vcpi.num_slots;
+	mutex_unlock(&mgr->lock);
+
 	port->vcpi.num_slots = 0;
 	drm_dp_put_port(port);
 }
diff --git a/drivers/gpu/drm/i915/intel_dp_mst.c b/drivers/gpu/drm/i915/intel_dp_mst.c
index 4280a83..bad9300 100644
--- a/drivers/gpu/drm/i915/intel_dp_mst.c
+++ b/drivers/gpu/drm/i915/intel_dp_mst.c
@@ -42,6 +42,8 @@ static bool intel_dp_mst_compute_config(struct intel_encoder *encoder,
 	int lane_count, slots;
 	const struct drm_display_mode *adjusted_mode = &pipe_config->base.adjusted_mode;
 	int mst_pbn;
+	struct intel_connector *connector =
+		to_intel_connector(conn_state->connector);
 
 	pipe_config->dp_encoder_is_mst = true;
 	pipe_config->has_pch_encoder = false;
@@ -62,7 +64,8 @@ static bool intel_dp_mst_compute_config(struct intel_encoder *encoder,
 	mst_pbn = drm_dp_calc_pbn_mode(adjusted_mode->crtc_clock, bpp);
 
 	pipe_config->pbn = mst_pbn;
-	slots = drm_dp_find_vcpi_slots(&intel_dp->mst_mgr, mst_pbn);
+	slots = drm_dp_find_vcpi_slots(&intel_dp->mst_mgr, connector->port,
+				       mst_pbn);
 	if (slots < 0) {
 		DRM_ERROR("not enough available time slots for pbn=%d", mst_pbn);
 		return false;
diff --git a/include/drm/drm_dp_mst_helper.h b/include/drm/drm_dp_mst_helper.h
index 0032076..5c55528 100644
--- a/include/drm/drm_dp_mst_helper.h
+++ b/include/drm/drm_dp_mst_helper.h
@@ -590,7 +590,7 @@ void drm_dp_mst_deallocate_vcpi(struct drm_dp_mst_topology_mgr *mgr,
 
 
 int drm_dp_find_vcpi_slots(struct drm_dp_mst_topology_mgr *mgr,
-			   int pbn);
+			   struct drm_dp_mst_port *port, int pbn);
 
 
 int drm_dp_update_payload_part1(struct drm_dp_mst_topology_mgr *mgr);
-- 
2.7.4