NTB: ntb_perf: Clear stale values in doorbell and command SPAD register

when ntb_perf is unloaded, the command scratchpad register still
retains the last initialized value of PERF_CMD_INVAL. When ntb_perf
is re-loaded and reads peer command scratchpad register and it mis
interprets the peer state as initialized.

To avoid this, clearing the local side command scratchpad register
in perf_disable_service
Signed-off-by: Sanjay R Mehta <sanju.mehta@amd.com>
Acked-by: Allen Hubbe <allenbh@gmail.com>
Acked-by: Logan Gunthorpe <logang@deltatee.com>
Acked-by: Serge Semin <fancer.lancer@gmail.com>
Signed-off-by: Jon Mason <jdmason@kudzu.us>

drivers/ntb/test/ntb_perf.c

@@ -751,6 +751,14 @@ static void perf_disable_service(struct perf_ctx *perf)
 	for (pidx = 0; pidx < perf->pcnt; pidx++)
 		flush_work(&perf->peers[pidx].service);
 
+	for (pidx = 0; pidx < perf->pcnt; pidx++) {
+		struct perf_peer *peer = &perf->peers[pidx];
+
+		ntb_spad_write(perf->ntb, PERF_SPAD_CMD(peer->gidx), 0);
+	}
+
+	ntb_db_clear(perf->ntb, PERF_SPAD_NOTIFY(perf->gidx));
+
 	ntb_link_disable(perf->ntb);
 }