[PATCH 5.10 078/120] drm/dp/mst: Export drm_dp_get_vc_payload_bw()

[Greg Kroah-Hartman]

From: Imre Deak <imre.deak at intel.com>

commit 83404d581471775f37f85e5261ec0d09407d8bed upstream.

This function will be needed by the next patch where the driver
calculates the BW based on driver specific parameters, so export it.

At the same time sanitize the function params, passing the more natural
link rate instead of the encoding of the same rate.

v2:
- Fix function documentation. (Lyude)

Cc: Lyude Paul <lyude at redhat.com>
Cc: Ville Syrjala <ville.syrjala at intel.com>
Cc: <stable at vger.kernel.org>
Cc: dri-devel at lists.freedesktop.org
Signed-off-by: Imre Deak <imre.deak at intel.com>
Reviewed-by: Lyude Paul <lyude at redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210125173636.1733812-1-imre.deak@intel.com
(cherry picked from commit a321fc2b4e60fc1b39517d26c8104351636a6062)
Signed-off-by: Jani Nikula <jani.nikula at intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
---
 drivers/gpu/drm/drm_dp_mst_topology.c |   24 ++++++++++++++++++------
 include/drm/drm_dp_mst_helper.h       |    1 +
 2 files changed, 19 insertions(+), 6 deletions(-)

--- a/drivers/gpu/drm/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/drm_dp_mst_topology.c
@@ -3629,14 +3629,26 @@ static int drm_dp_send_up_ack_reply(stru
 	return 0;
 }
 
-static int drm_dp_get_vc_payload_bw(u8 dp_link_bw, u8  dp_link_count)
+/**
+ * drm_dp_get_vc_payload_bw - get the VC payload BW for an MST link
+ * @link_rate: link rate in 10kbits/s units
+ * @link_lane_count: lane count
+ *
+ * Calculate the total bandwidth of a MultiStream Transport link. The returned
+ * 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.
+ */
+int drm_dp_get_vc_payload_bw(int link_rate, int link_lane_count)
 {
-	if (dp_link_bw == 0 || dp_link_count == 0)
-		DRM_DEBUG_KMS("invalid link bandwidth in DPCD: %x (link count: %d)\n",
-			      dp_link_bw, dp_link_count);
+	if (link_rate == 0 || link_lane_count == 0)
+		DRM_DEBUG_KMS("invalid link rate/lane count: (%d / %d)\n",
+			      link_rate, link_lane_count);
 
-	return dp_link_bw * dp_link_count / 2;
+	/* See DP v2.0 2.6.4.2, VCPayload_Bandwidth_for_OneTimeSlotPer_MTP_Allocation */
+	return link_rate * link_lane_count / 54000;
 }
+EXPORT_SYMBOL(drm_dp_get_vc_payload_bw);
 
 /**
  * drm_dp_read_mst_cap() - check whether or not a sink supports MST
@@ -3692,7 +3704,7 @@ int drm_dp_mst_topology_mgr_set_mst(stru
 			goto out_unlock;
 		}
 
-		mgr->pbn_div = drm_dp_get_vc_payload_bw(mgr->dpcd[1],
+		mgr->pbn_div = drm_dp_get_vc_payload_bw(drm_dp_bw_code_to_link_rate(mgr->dpcd[1]),
 							mgr->dpcd[2] & DP_MAX_LANE_COUNT_MASK);
 		if (mgr->pbn_div == 0) {
 			ret = -EINVAL;
--- a/include/drm/drm_dp_mst_helper.h
+++ b/include/drm/drm_dp_mst_helper.h
@@ -783,6 +783,7 @@ drm_dp_mst_detect_port(struct drm_connec
 
 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(int link_rate, int link_lane_count);
 
 int drm_dp_calc_pbn_mode(int clock, int bpp, bool dsc);