drm/mst: Separate sideband packet header parsing from message building

In preparation of per-branch device down message handling, separate
header parsing from message building. This will allow us to peek at
figure out which branch device the message is from before starting to
parse the message contents.
Reviewed-by: Lyude Paul <lyude@redhat.com>
Reviewed-by: Wayne Lin <waynelin@amd.com>
[seanpaul s/drm_dp_sideband_msg_build/drm_dp_sideband_msg_set_header/]
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20200213211523.156998-2-sean@poorly.run

drivers/gpu/drm/drm_dp_mst_topology.c

@@ -687,51 +687,45 @@ static void drm_dp_encode_sideband_reply(struct drm_dp_sideband_msg_reply_body *
 	raw->cur_len = idx;
 }
 
-/* this adds a chunk of msg to the builder to get the final msg */
-static bool drm_dp_sideband_msg_build(struct drm_dp_sideband_msg_rx *msg,
-				      u8 *replybuf, u8 replybuflen, bool hdr)
+static int drm_dp_sideband_msg_set_header(struct drm_dp_sideband_msg_rx *msg,
+					  struct drm_dp_sideband_msg_hdr *hdr,
+					  u8 hdrlen)
 {
-	int ret;
-	u8 crc4;
+	/*
+	 * ignore out-of-order messages or messages that are part of a
+	 * failed transaction
+	 */
+	if (!hdr->somt && !msg->have_somt)
+		return false;
 
-	if (hdr) {
-		u8 hdrlen;
-		struct drm_dp_sideband_msg_hdr recv_hdr;
-		ret = drm_dp_decode_sideband_msg_hdr(&recv_hdr, replybuf, replybuflen, &hdrlen);
-		if (ret == false) {
-			print_hex_dump(KERN_DEBUG, "failed hdr", DUMP_PREFIX_NONE, 16, 1, replybuf, replybuflen, false);
-			return false;
-		}
+	/* get length contained in this portion */
+	msg->curchunk_idx = 0;
+	msg->curchunk_len = hdr->msg_len;
+	msg->curchunk_hdrlen = hdrlen;
 
-		/*
-		 * ignore out-of-order messages or messages that are part of a
-		 * failed transaction
-		 */
-		if (!recv_hdr.somt && !msg->have_somt)
-			return false;
+	/* we have already gotten an somt - don't bother parsing */
+	if (hdr->somt && msg->have_somt)
+		return false;
 
-		/* get length contained in this portion */
-		msg->curchunk_len = recv_hdr.msg_len;
-		msg->curchunk_hdrlen = hdrlen;
+	if (hdr->somt) {
+		memcpy(&msg->initial_hdr, hdr,
+		       sizeof(struct drm_dp_sideband_msg_hdr));
+		msg->have_somt = true;
+	}
+	if (hdr->eomt)
+		msg->have_eomt = true;
 
-		/* we have already gotten an somt - don't bother parsing */
-		if (recv_hdr.somt && msg->have_somt)
-			return false;
+	return true;
+}
 
-		if (recv_hdr.somt) {
-			memcpy(&msg->initial_hdr, &recv_hdr, sizeof(struct drm_dp_sideband_msg_hdr));
-			msg->have_somt = true;
-		}
-		if (recv_hdr.eomt)
-			msg->have_eomt = true;
+/* this adds a chunk of msg to the builder to get the final msg */
+static bool drm_dp_sideband_append_payload(struct drm_dp_sideband_msg_rx *msg,
+					   u8 *replybuf, u8 replybuflen)
+{
+	u8 crc4;
 
-		/* copy the bytes for the remainder of this header chunk */
-		msg->curchunk_idx = min(msg->curchunk_len, (u8)(replybuflen - hdrlen));
-		memcpy(&msg->chunk[0], replybuf + hdrlen, msg->curchunk_idx);
-	} else {
-		memcpy(&msg->chunk[msg->curchunk_idx], replybuf, replybuflen);
-		msg->curchunk_idx += replybuflen;
-	}
+	memcpy(&msg->chunk[msg->curchunk_idx], replybuf, replybuflen);
+	msg->curchunk_idx += replybuflen;
 
 	if (msg->curchunk_idx >= msg->curchunk_len) {
 		/* do CRC */
@@ -3708,25 +3702,43 @@ static bool drm_dp_get_one_sb_msg(struct drm_dp_mst_topology_mgr *mgr, bool up)
 	u8 replyblock[32];
 	int replylen, curreply;
 	int ret;
+	u8 hdrlen;
+	struct drm_dp_sideband_msg_hdr hdr;
 	struct drm_dp_sideband_msg_rx *msg;
-	int basereg = up ? DP_SIDEBAND_MSG_UP_REQ_BASE : DP_SIDEBAND_MSG_DOWN_REP_BASE;
+	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;
 
 	len = min(mgr->max_dpcd_transaction_bytes, 16);
-	ret = drm_dp_dpcd_read(mgr->aux, basereg,
-			       replyblock, len);
+	ret = drm_dp_dpcd_read(mgr->aux, basereg, replyblock, len);
 	if (ret != len) {
 		DRM_DEBUG_KMS("failed to read DPCD down rep %d %d\n", len, ret);
 		return false;
 	}
-	ret = drm_dp_sideband_msg_build(msg, replyblock, len, true);
+
+	ret = drm_dp_decode_sideband_msg_hdr(&hdr, replyblock, len, &hdrlen);
+	if (ret == false) {
+		print_hex_dump(KERN_DEBUG, "failed hdr", DUMP_PREFIX_NONE, 16,
+			       1, replyblock, len, false);
+		DRM_DEBUG_KMS("ERROR: failed header\n");
+		return false;
+	}
+
+	if (!drm_dp_sideband_msg_set_header(msg, &hdr, hdrlen)) {
+		DRM_DEBUG_KMS("sideband msg set header failed %d\n",
+			      replyblock[0]);
+		return false;
+	}
+
+	replylen = min(msg->curchunk_len, (u8)(len - hdrlen));
+	ret = drm_dp_sideband_append_payload(msg, replyblock + hdrlen, replylen);
 	if (!ret) {
 		DRM_DEBUG_KMS("sideband msg build failed %d\n", replyblock[0]);
 		return false;
 	}
-	replylen = msg->curchunk_len + msg->curchunk_hdrlen;
 
-	replylen -= len;
+	replylen = msg->curchunk_len + msg->curchunk_hdrlen - len;
 	curreply = len;
 	while (replylen > 0) {
 		len = min3(replylen, mgr->max_dpcd_transaction_bytes, 16);
@@ -3738,7 +3750,7 @@ static bool drm_dp_get_one_sb_msg(struct drm_dp_mst_topology_mgr *mgr, bool up)
 			return false;
 		}
 
-		ret = drm_dp_sideband_msg_build(msg, replyblock, len, false);
+		ret = drm_dp_sideband_append_payload(msg, replyblock, len);
 		if (!ret) {
 			DRM_DEBUG_KMS("failed to build sideband msg\n");
 			return false;