drm/dp_mst: Store the MST PBN divider value in fixed point format

On UHBR links the PBN divider is a fractional number, accordingly store
it in fixed point format. For now drm_dp_get_vc_payload_bw() always
returns a whole number and all callers will use only the integer part of
it which should preserve the current behavior. The next patch will fix
drm_dp_get_vc_payload_bw() for UHBR rates returning a fractional number
for those (also accounting for the channel coding efficiency correctly).

Cc: Lyude Paul <lyude@redhat.com>
Cc: Harry Wentland <harry.wentland@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: Wayne Lin <wayne.lin@amd.com>
Cc: amd-gfx@lists.freedesktop.org
Cc: dri-devel@lists.freedesktop.org
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Acked-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
[Rebased changes in dm_helpers_construct_old_payload() on drm-intel-next]
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231116131841.1588781-2-imre.deak@intel.com

drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c

@@ -85,6 +85,7 @@
 #include <drm/drm_atomic_uapi.h>
 #include <drm/drm_atomic_helper.h>
 #include <drm/drm_blend.h>
+#include <drm/drm_fixed.h>
 #include <drm/drm_fourcc.h>
 #include <drm/drm_edid.h>
 #include <drm/drm_vblank.h>
@@ -6863,8 +6864,8 @@ static int dm_encoder_helper_atomic_check(struct drm_encoder *encoder,
 	if (IS_ERR(mst_state))
 		return PTR_ERR(mst_state);
 
-	if (!mst_state->pbn_div)
+	if (!mst_state->pbn_div.full)
-		mst_state->pbn_div = dm_mst_get_pbn_divider(aconnector->mst_root->dc_link);
+		mst_state->pbn_div.full = dfixed_const(dm_mst_get_pbn_divider(aconnector->mst_root->dc_link));
 
 	if (!state->duplicated) {
 		int max_bpc = conn_state->max_requested_bpc;

drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_helpers.c

@@ -31,6 +31,7 @@
 #include <drm/drm_probe_helper.h>
 #include <drm/amdgpu_drm.h>
 #include <drm/drm_edid.h>
+#include <drm/drm_fixed.h>
 
 #include "dm_services.h"
 #include "amdgpu.h"
@@ -205,13 +206,14 @@ void dm_helpers_dp_update_branch_info(
 
 static void dm_helpers_construct_old_payload(
 			struct dc_link *link,
-			int pbn_per_slot,
+			fixed20_12 pbn_per_slot_fp,
 			struct drm_dp_mst_atomic_payload *new_payload,
 			struct drm_dp_mst_atomic_payload *old_payload)
 {
 	struct link_mst_stream_allocation_table current_link_table =
 									link->mst_stream_alloc_table;
 	struct link_mst_stream_allocation *dc_alloc;
+	int pbn_per_slot = dfixed_trunc(pbn_per_slot_fp);
 	int i;
 
 	*old_payload = *new_payload;

drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c

@@ -27,6 +27,7 @@
 #include <drm/display/drm_dp_mst_helper.h>
 #include <drm/drm_atomic.h>
 #include <drm/drm_atomic_helper.h>
+#include <drm/drm_fixed.h>
 #include "dm_services.h"
 #include "amdgpu.h"
 #include "amdgpu_dm.h"
@@ -935,10 +936,10 @@ static int increase_dsc_bpp(struct drm_atomic_state *state,
 		link_timeslots_used = 0;
 
 		for (i = 0; i < count; i++)
-			link_timeslots_used += DIV_ROUND_UP(vars[i + k].pbn, mst_state->pbn_div);
+			link_timeslots_used += DIV_ROUND_UP(vars[i + k].pbn, dfixed_trunc(mst_state->pbn_div));
 
 		fair_pbn_alloc =
-			(63 - link_timeslots_used) / remaining_to_increase * mst_state->pbn_div;
+			(63 - link_timeslots_used) / remaining_to_increase * dfixed_trunc(mst_state->pbn_div);
 
 		if (initial_slack[next_index] > fair_pbn_alloc) {
 			vars[next_index].pbn += fair_pbn_alloc;

drivers/gpu/drm/display/drm_dp_mst_topology.c

@@ -43,6 +43,7 @@
 #include <drm/drm_atomic_helper.h>
 #include <drm/drm_drv.h>
 #include <drm/drm_edid.h>
+#include <drm/drm_fixed.h>
 #include <drm/drm_print.h>
 #include <drm/drm_probe_helper.h>
 
@@ -3578,16 +3579,22 @@ static int drm_dp_send_up_ack_reply(struct drm_dp_mst_topology_mgr *mgr,
  * value is in units of PBNs/(timeslots/1 MTP). This value can be used to
  * convert the number of PBNs required for a given stream to the number of
  * timeslots this stream requires in each MTP.
+ *
+ * Returns the BW / timeslot value in 20.12 fixed point format.
  */
-int drm_dp_get_vc_payload_bw(const struct drm_dp_mst_topology_mgr *mgr,
+fixed20_12 drm_dp_get_vc_payload_bw(const struct drm_dp_mst_topology_mgr *mgr,
-			     int link_rate, int link_lane_count)
+				    int link_rate, int link_lane_count)
 {
+	fixed20_12 ret;
+
 	if (link_rate == 0 || link_lane_count == 0)
 		drm_dbg_kms(mgr->dev, "invalid link rate/lane count: (%d / %d)\n",
 			    link_rate, link_lane_count);
 
 	/* See DP v2.0 2.6.4.2, VCPayload_Bandwidth_for_OneTimeSlotPer_MTP_Allocation */
-	return link_rate * link_lane_count / 54000;
+	ret.full = dfixed_const(link_rate * link_lane_count / 54000);
+
+	return ret;
 }
 EXPORT_SYMBOL(drm_dp_get_vc_payload_bw);
 
@@ -4335,7 +4342,7 @@ int drm_dp_atomic_find_time_slots(struct drm_atomic_state *state,
 		}
 	}
 
-	req_slots = DIV_ROUND_UP(pbn, topology_state->pbn_div);
+	req_slots = DIV_ROUND_UP(pbn, dfixed_trunc(topology_state->pbn_div));
 
 	drm_dbg_atomic(mgr->dev, "[CONNECTOR:%d:%s] [MST PORT:%p] TU %d -> %d\n",
 		       port->connector->base.id, port->connector->name,
@@ -4872,7 +4879,8 @@ void drm_dp_mst_dump_topology(struct seq_file *m,
 	state = to_drm_dp_mst_topology_state(mgr->base.state);
 	seq_printf(m, "\n*** Atomic state info ***\n");
 	seq_printf(m, "payload_mask: %x, max_payloads: %d, start_slot: %u, pbn_div: %d\n",
-		   state->payload_mask, mgr->max_payloads, state->start_slot, state->pbn_div);
+		   state->payload_mask, mgr->max_payloads, state->start_slot,
+		   dfixed_trunc(state->pbn_div));
 
 	seq_printf(m, "\n| idx | port | vcpi | slots | pbn | dsc | status |     sink name     |\n");
 	for (i = 0; i < mgr->max_payloads; i++) {
@@ -5330,10 +5338,10 @@ drm_dp_mst_atomic_check_payload_alloc_limits(struct drm_dp_mst_topology_mgr *mgr
 	}
 
 	if (!payload_count)
-		mst_state->pbn_div = 0;
+		mst_state->pbn_div.full = dfixed_const(0);
 
 	drm_dbg_atomic(mgr->dev, "[MST MGR:%p] mst state %p TU pbn_div=%d avail=%d used=%d\n",
-		       mgr, mst_state, mst_state->pbn_div, avail_slots,
+		       mgr, mst_state, dfixed_trunc(mst_state->pbn_div), avail_slots,
 		       mst_state->total_avail_slots - avail_slots);
 
 	return 0;

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

@@ -26,6 +26,7 @@
 #include <drm/drm_atomic.h>
 #include <drm/drm_atomic_helper.h>
 #include <drm/drm_edid.h>
+#include <drm/drm_fixed.h>
 #include <drm/drm_probe_helper.h>
 
 #include "i915_drv.h"
@@ -202,7 +203,7 @@ static int intel_dp_mst_find_vcpi_slots_for_bpp(struct intel_encoder *encoder,
 		 */
 		drm_WARN_ON(&i915->drm, remote_m_n.tu < crtc_state->dp_m_n.tu);
 		crtc_state->dp_m_n.tu = remote_m_n.tu;
-		crtc_state->pbn = remote_m_n.tu * mst_state->pbn_div;
+		crtc_state->pbn = remote_m_n.tu * dfixed_trunc(mst_state->pbn_div);
 
 		slots = drm_dp_atomic_find_time_slots(state, &intel_dp->mst_mgr,
 						      connector->port,

drivers/gpu/drm/nouveau/dispnv50/disp.c

@@ -39,6 +39,7 @@
 #include <drm/drm_atomic_helper.h>
 #include <drm/drm_edid.h>
 #include <drm/drm_fb_helper.h>
+#include <drm/drm_fixed.h>
 #include <drm/drm_probe_helper.h>
 #include <drm/drm_vblank.h>
 
@@ -945,7 +946,8 @@ nv50_msto_prepare(struct drm_atomic_state *state,
 	if (ret == 0) {
 		nvif_outp_dp_mst_vcpi(&mstm->outp->outp, msto->head->base.index,
 				      payload->vc_start_slot, payload->time_slots,
-				      payload->pbn, payload->time_slots * mst_state->pbn_div);
+				      payload->pbn,
+				      payload->time_slots * dfixed_trunc(mst_state->pbn_div));
 	} else {
 		nvif_outp_dp_mst_vcpi(&mstm->outp->outp, msto->head->base.index, 0, 0, 0, 0);
 	}
@@ -989,7 +991,7 @@ nv50_msto_atomic_check(struct drm_encoder *encoder,
 	if (IS_ERR(mst_state))
 		return PTR_ERR(mst_state);
 
-	if (!mst_state->pbn_div) {
+	if (!mst_state->pbn_div.full) {
 		struct nouveau_encoder *outp = mstc->mstm->outp;
 
 		mst_state->pbn_div = drm_dp_get_vc_payload_bw(&mstm->mgr,

include/drm/display/drm_dp_mst_helper.h

@@ -25,6 +25,7 @@
 #include <linux/types.h>
 #include <drm/display/drm_dp_helper.h>
 #include <drm/drm_atomic.h>
+#include <drm/drm_fixed.h>
 
 #if IS_ENABLED(CONFIG_DRM_DEBUG_DP_MST_TOPOLOGY_REFS)
 #include <linux/stackdepot.h>
@@ -617,7 +618,7 @@ struct drm_dp_mst_topology_state {
 	 * @pbn_div: The current PBN divisor for this topology. The driver is expected to fill this
 	 * out itself.
 	 */
-	int pbn_div;
+	fixed20_12 pbn_div;
 };
 
 #define to_dp_mst_topology_mgr(x) container_of(x, struct drm_dp_mst_topology_mgr, base)
@@ -839,8 +840,8 @@ struct edid *drm_dp_mst_get_edid(struct drm_connector *connector,
 				 struct drm_dp_mst_topology_mgr *mgr,
 				 struct drm_dp_mst_port *port);
 
-int drm_dp_get_vc_payload_bw(const struct drm_dp_mst_topology_mgr *mgr,
+fixed20_12 drm_dp_get_vc_payload_bw(const struct drm_dp_mst_topology_mgr *mgr,
-			     int link_rate, int link_lane_count);
+				    int link_rate, int link_lane_count);
 
 int drm_dp_calc_pbn_mode(int clock, int bpp);