drm/mst: Support simultaneous down replies

Currently we have one down reply message servicing the mst manager, so
we need to serialize all tx msgs to ensure we only have one message in
flight at a time. For obvious reasons this is suboptimal (but less
suboptimal than the free-for-all we had before serialization).

This patch removes the single down_rep_recv message from manager and
adds 2 replies in the branch structure. The 2 replies mirrors the tx_slots
which we use to rate-limit outgoing messages and correspond to seqno in
the packet headers.

Cc: Wayne Lin <[e-mail]>
Reviewed-by: Lyude Paul <[e-mail]>
Reviewed-by: Wayne Lin <[e-mail]>
Signed-off-by: Sean Paul <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]

drivers/gpu/drm/drm_dp_mst_topology.c

···
 }
 EXPORT_SYMBOL(drm_dp_mst_topology_mgr_resume);
 
-static bool drm_dp_get_one_sb_msg(struct drm_dp_mst_topology_mgr *mgr, bool up)
+static bool drm_dp_get_one_sb_msg(struct drm_dp_mst_topology_mgr *mgr, bool up,
+				  struct drm_dp_mst_branch **mstb, int *seqno)
 {
 	int len;
 	u8 replyblock[32];
···
 	int basereg = up ? DP_SIDEBAND_MSG_UP_REQ_BASE :
 			   DP_SIDEBAND_MSG_DOWN_REP_BASE;
 
-	msg = up ? &mgr->up_req_recv : &mgr->down_rep_recv;
+	*mstb = NULL;
+	*seqno = -1;
 
 	len = min(mgr->max_dpcd_transaction_bytes, 16);
 	ret = drm_dp_dpcd_read(mgr->aux, basereg, replyblock, len);
···
 			       1, replyblock, len, false);
 		DRM_DEBUG_KMS("ERROR: failed header\n");
 		return false;
+	}
+
+	*seqno = hdr.seqno;
+
+	if (up) {
+		msg = &mgr->up_req_recv;
+	} else {
+		/* Caller is responsible for giving back this reference */
+		*mstb = drm_dp_get_mst_branch_device(mgr, hdr.lct, hdr.rad);
+		if (!*mstb) {
+			DRM_DEBUG_KMS("Got MST reply from unknown device %d\n",
+				      hdr.lct);
+			return false;
+		}
+		msg = &(*mstb)->down_rep_recv[hdr.seqno];
 	}
 
 	if (!drm_dp_sideband_msg_set_header(msg, &hdr, hdrlen)) {
···
 static int drm_dp_mst_handle_down_rep(struct drm_dp_mst_topology_mgr *mgr)
 {
 	struct drm_dp_sideband_msg_tx *txmsg;
-	struct drm_dp_mst_branch *mstb;
-	struct drm_dp_sideband_msg_hdr *hdr = &mgr->down_rep_recv.initial_hdr;
-	int slot = -1;
+	struct drm_dp_mst_branch *mstb = NULL;
+	struct drm_dp_sideband_msg_rx *msg = NULL;
+	int seqno = -1;
 
-	if (!drm_dp_get_one_sb_msg(mgr, false))
-		goto clear_down_rep_recv;
+	if (!drm_dp_get_one_sb_msg(mgr, false, &mstb, &seqno))
+		goto out_clear_reply;
 
-	if (!mgr->down_rep_recv.have_eomt)
-		return 0;
+	msg = &mstb->down_rep_recv[seqno];
 
-	mstb = drm_dp_get_mst_branch_device(mgr, hdr->lct, hdr->rad);
-	if (!mstb) {
-		DRM_DEBUG_KMS("Got MST reply from unknown device %d\n",
-			      hdr->lct);
-		goto clear_down_rep_recv;
-	}
+	/* Multi-packet message transmission, don't clear the reply */
+	if (!msg->have_eomt)
+		goto out;
 
 	/* find the message */
-	slot = hdr->seqno;
 	mutex_lock(&mgr->qlock);
-	txmsg = mstb->tx_slots[slot];
+	txmsg = mstb->tx_slots[seqno];
 	/* remove from slots */
 	mutex_unlock(&mgr->qlock);
 
 	if (!txmsg) {
+		struct drm_dp_sideband_msg_hdr *hdr;
+		hdr = &msg->initial_hdr;
 		DRM_DEBUG_KMS("Got MST reply with no msg %p %d %d %02x %02x\n",
 			      mstb, hdr->seqno, hdr->lct, hdr->rad[0],
-			      mgr->down_rep_recv.msg[0]);
-		goto no_msg;
+			      msg->msg[0]);
+		goto out_clear_reply;
 	}
 
-	drm_dp_sideband_parse_reply(&mgr->down_rep_recv, &txmsg->reply);
+	drm_dp_sideband_parse_reply(msg, &txmsg->reply);
 
-	if (txmsg->reply.reply_type == DP_SIDEBAND_REPLY_NAK)
+	if (txmsg->reply.reply_type == DP_SIDEBAND_REPLY_NAK) {
 		DRM_DEBUG_KMS("Got NAK reply: req 0x%02x (%s), reason 0x%02x (%s), nak data 0x%02x\n",
 			      txmsg->reply.req_type,
 			      drm_dp_mst_req_type_str(txmsg->reply.req_type),
 			      txmsg->reply.u.nak.reason,
 			      drm_dp_mst_nak_reason_str(txmsg->reply.u.nak.reason),
 			      txmsg->reply.u.nak.nak_data);
+		goto out_clear_reply;
+	}
 
-	memset(&mgr->down_rep_recv, 0, sizeof(struct drm_dp_sideband_msg_rx));
+	memset(msg, 0, sizeof(struct drm_dp_sideband_msg_rx));
 	drm_dp_mst_topology_put_mstb(mstb);
 
 	mutex_lock(&mgr->qlock);
 	txmsg->state = DRM_DP_SIDEBAND_TX_RX;
-	mstb->tx_slots[slot] = NULL;
+	mstb->tx_slots[seqno] = NULL;
 	mgr->is_waiting_for_dwn_reply = false;
 	mutex_unlock(&mgr->qlock);
 
···
 
 	return 0;
 
-no_msg:
-	drm_dp_mst_topology_put_mstb(mstb);
-clear_down_rep_recv:
+out_clear_reply:
 	mutex_lock(&mgr->qlock);
 	mgr->is_waiting_for_dwn_reply = false;
 	mutex_unlock(&mgr->qlock);
-	memset(&mgr->down_rep_recv, 0, sizeof(struct drm_dp_sideband_msg_rx));
+	if (msg)
+		memset(msg, 0, sizeof(struct drm_dp_sideband_msg_rx));
+out:
+	if (mstb)
+		drm_dp_mst_topology_put_mstb(mstb);
 
 	return 0;
 }
···
 
 static int drm_dp_mst_handle_up_req(struct drm_dp_mst_topology_mgr *mgr)
 {
-	struct drm_dp_sideband_msg_hdr *hdr = &mgr->up_req_recv.initial_hdr;
 	struct drm_dp_pending_up_req *up_req;
-	bool seqno;
+	int seqno;
 
-	if (!drm_dp_get_one_sb_msg(mgr, true))
+	if (!drm_dp_get_one_sb_msg(mgr, true, NULL, &seqno))
 		goto out;
 
 	if (!mgr->up_req_recv.have_eomt)
···
 	}
 	INIT_LIST_HEAD(&up_req->next);
 
-	seqno = hdr->seqno;
 	drm_dp_sideband_parse_req(&mgr->up_req_recv, &up_req->msg);
 
 	if (up_req->msg.req_type != DP_CONNECTION_STATUS_NOTIFY &&
···
 			      res_stat->available_pbn);
 	}
 
-	up_req->hdr = *hdr;
+	up_req->hdr = mgr->up_req_recv.initial_hdr;
 	mutex_lock(&mgr->up_req_lock);
 	list_add_tail(&up_req->next, &mgr->up_req_list);
 	mutex_unlock(&mgr->up_req_lock);

include/drm/drm_dp_mst_helper.h

···
 	bool fec_capable;
 };
 
+/* sideband msg header - not bit struct */
+struct drm_dp_sideband_msg_hdr {
+	u8 lct;
+	u8 lcr;
+	u8 rad[8];
+	bool broadcast;
+	bool path_msg;
+	u8 msg_len;
+	bool somt;
+	bool eomt;
+	bool seqno;
+};
+
+struct drm_dp_sideband_msg_rx {
+	u8 chunk[48];
+	u8 msg[256];
+	u8 curchunk_len;
+	u8 curchunk_idx; /* chunk we are parsing now */
+	u8 curchunk_hdrlen;
+	u8 curlen; /* total length of the msg */
+	bool have_somt;
+	bool have_eomt;
+	struct drm_dp_sideband_msg_hdr initial_hdr;
+};
+
 /**
  * struct drm_dp_mst_branch - MST branch device.
  * @rad: Relative Address to talk to this branch device.
···
 	int last_seqno;
 	bool link_address_sent;
 
+	/**
+	 * @down_rep_recv: Message receiver state for down replies.
+	 */
+	struct drm_dp_sideband_msg_rx down_rep_recv[2];
+
 	/* global unique identifier to identify branch devices */
 	u8 guid[16];
 };
 
-
-/* sideband msg header - not bit struct */
-struct drm_dp_sideband_msg_hdr {
-	u8 lct;
-	u8 lcr;
-	u8 rad[8];
-	bool broadcast;
-	bool path_msg;
-	u8 msg_len;
-	bool somt;
-	bool eomt;
-	bool seqno;
-};
 
 struct drm_dp_nak_reply {
 	u8 guid[16];
···
 	u8 port_number;
 };
 
-
-struct drm_dp_sideband_msg_rx {
-	u8 chunk[48];
-	u8 msg[256];
-	u8 curchunk_len;
-	u8 curchunk_idx; /* chunk we are parsing now */
-	u8 curchunk_hdrlen;
-	u8 curlen; /* total length of the msg */
-	bool have_somt;
-	bool have_eomt;
-	struct drm_dp_sideband_msg_hdr initial_hdr;
-};
 
 #define DRM_DP_MAX_SDP_STREAMS 16
 struct drm_dp_allocate_payload {
···
 	 */
 	int conn_base_id;
 
-	/**
-	 * @down_rep_recv: Message receiver state for down replies.
-	 */
-	struct drm_dp_sideband_msg_rx down_rep_recv;
 	/**
 	 * @up_req_recv: Message receiver state for up requests.
 	 */