Index: head/sys/conf/files.powerpc
===================================================================
--- head/sys/conf/files.powerpc
+++ head/sys/conf/files.powerpc
@@ -262,6 +262,7 @@
 powerpc/pseries/phyp-hvcall.S	optional	pseries powerpc64
 powerpc/pseries/mmu_phyp.c	optional	pseries powerpc64
 powerpc/pseries/phyp_console.c	optional	pseries powerpc64 uart
+powerpc/pseries/phyp_dbg.c	optional	pseries powerpc64 gdb
 powerpc/pseries/phyp_llan.c	optional	llan
 powerpc/pseries/phyp_vscsi.c	optional	pseries powerpc64 scbus
 powerpc/pseries/platform_chrp.c	optional	pseries
Index: head/sys/powerpc/pseries/phyp_dbg.c
===================================================================
--- head/sys/powerpc/pseries/phyp_dbg.c
+++ head/sys/powerpc/pseries/phyp_dbg.c
@@ -0,0 +1,163 @@
+/*-
+ * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
+ *
+ * Copyright (C) 2019 Leandro Lupori
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
+ * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
+ * IN NO EVENT SHALL TOOLS GMBH BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+ * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
+ * OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
+ * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
+ * OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
+ * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <sys/cdefs.h>
+__FBSDID("$FreeBSD$");
+
+#include <sys/linker_set.h>
+
+#include <dev/ofw/openfirm.h>
+#include <gdb/gdb.h>
+
+#include "phyp-hvcall.h"
+
+static gdb_probe_f uart_phyp_dbg_probe;
+static gdb_init_f uart_phyp_dbg_init;
+static gdb_term_f uart_phyp_dbg_term;
+static gdb_getc_f uart_phyp_dbg_getc;
+static gdb_putc_f uart_phyp_dbg_putc;
+
+GDB_DBGPORT(uart_phyp, uart_phyp_dbg_probe,
+    uart_phyp_dbg_init, uart_phyp_dbg_term,
+    uart_phyp_dbg_getc, uart_phyp_dbg_putc);
+
+static struct uart_phyp_dbgport {
+	cell_t vtermid;
+	union {
+		uint64_t u64[2];
+		char str[16];
+	} inbuf;
+	uint64_t inbuflen;
+} dbgport;
+
+static int
+uart_phyp_dbg_probe(void)
+{
+	char buf[64];
+	cell_t reg;
+	phandle_t vty;
+
+	if (!getenv_string("hw.uart_phyp.dbgport", buf, sizeof(buf)))
+		return (-1);
+
+	if ((vty = OF_finddevice(buf)) == -1)
+		return (-1);
+
+	if (OF_getprop(vty, "name", buf, sizeof(buf)) <= 0)
+		return (-1);
+	if (strcmp(buf, "vty") != 0)
+		return (-1);
+
+	if (OF_getprop(vty, "device_type", buf, sizeof(buf)) == -1)
+		return (-1);
+	if (strcmp(buf, "serial") != 0)
+		return (-1);
+
+	if (OF_getprop(vty, "compatible", buf, sizeof(buf)) <= 0)
+		return (-1);
+	if (strcmp(buf, "hvterm1") != 0)
+		return (-1);
+
+	reg = ~0U;
+	OF_getencprop(vty, "reg", &reg, sizeof(reg));
+	if (reg == ~0U)
+		return (-1);
+
+	dbgport.vtermid = reg;
+	dbgport.inbuflen = 0;
+
+	return (0);
+}
+
+static void
+uart_phyp_dbg_init(void)
+{
+}
+
+static void
+uart_phyp_dbg_term(void)
+{
+}
+
+static int
+uart_phyp_dbg_getc(void)
+{
+	int c, err, next;
+
+	if (dbgport.inbuflen == 0) {
+		err = phyp_pft_hcall(H_GET_TERM_CHAR, dbgport.vtermid,
+		    0, 0, 0, &dbgport.inbuflen, &dbgport.inbuf.u64[0],
+		    &dbgport.inbuf.u64[1]);
+		if (err != H_SUCCESS)
+			return (-1);
+	}
+
+	if (dbgport.inbuflen == 0)
+		return (-1);
+
+	c = dbgport.inbuf.str[0];
+	dbgport.inbuflen--;
+
+	if (dbgport.inbuflen == 0)
+		return (c);
+
+	/*
+	 * Since version 2.11.0, QEMU became bug-compatible
+	 * with PowerVM's vty, by inserting a \0 after every \r.
+	 * Filter it here.
+	 */
+	next = 1;
+	if (c == '\r' && dbgport.inbuf.str[next] == '\0') {
+		next++;
+		dbgport.inbuflen--;
+	}
+
+	if (dbgport.inbuflen > 0)
+		memmove(&dbgport.inbuf.str[0], &dbgport.inbuf.str[next],
+		    dbgport.inbuflen);
+
+	return (c);
+}
+
+static void
+uart_phyp_dbg_putc(int c)
+{
+	int	err;
+
+	union {
+		uint64_t u64;
+		unsigned char bytes[8];
+	} cbuf;
+
+	cbuf.bytes[0] = (unsigned char)c;
+
+	do {
+		err = phyp_hcall(H_PUT_TERM_CHAR, dbgport.vtermid, 1,
+		    cbuf.u64, 0);
+		DELAY(100);
+	} while (err == H_BUSY);
+}
+