xenvm: drivers: serial: Implement serial interface to Xen PV console

This commit adds minimal support of Xen hypervisor console via UART-like
driver. Implementation allows to use poll_in/poll_out char interface for
uart_console.c driver directly to HV console instead of using Xen
virtual PL011 UART. Future implementation will support interrupt driven
interface on Xen event channels, currently it is under development.

Also this commit introduces early console_io Xen interface, which allows
to receive printk/stdout messages quickly after start, but requires Xen,
built with CONFIG_DEBUG option.

Signed-off-by: Dmytro Firsov <dmytro_firsov@epam.com>

drivers/xen/CMakeLists.txt

@@ -0,0 +1,5 @@
+# SPDX-License-Identifier: Apache-2.0
+# Copyright (c) 2021 EPAM Systems
+
+zephyr_sources(hvm.c)
+zephyr_sources(events.c)

drivers/xen/events.c

@@ -0,0 +1,25 @@
+/*
+ * Copyright (c) 2021 EPAM Systems
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#include <arch/arm64/hypercall.h>
+#include <xen/public/xen.h>
+#include <xen/public/event_channel.h>
+#include <xen/events.h>
+
+void notify_evtchn(evtchn_port_t port)
+{
+	struct evtchn_send send;
+
+	if (port >= EVTCHN_2L_NR_CHANNELS) {
+		printk("%s: trying to send notify for invalid evtchn #%u\n",
+				__func__, port);
+		return;
+	}
+
+	send.port = port;
+
+	HYPERVISOR_event_channel_op(EVTCHNOP_send, &send);
+}

drivers/xen/hvm.c

@@ -0,0 +1,39 @@
+/*
+ * Copyright (c) 2021 EPAM Systems
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#include <arch/arm64/hypercall.h>
+#include <xen/hvm.h>
+#include <xen/public/hvm/hvm_op.h>
+#include <xen/public/hvm/params.h>
+
+#include <kernel.h>
+
+int hvm_set_parameter(int idx, uint64_t value)
+{
+	struct xen_hvm_param xhv;
+
+	xhv.domid = DOMID_SELF;
+	xhv.index = idx;
+	xhv.value = value;
+
+	return HYPERVISOR_hvm_op(HVMOP_set_param, &xhv);
+}
+
+int hvm_get_parameter(int idx, uint64_t *value)
+{
+	int ret = 0;
+	struct xen_hvm_param xhv;
+
+	xhv.domid = DOMID_SELF;
+	xhv.index = idx;
+
+	ret = HYPERVISOR_hvm_op(HVMOP_get_param, &xhv);
+	if (ret < 0)
+		return ret;
+
+	*value = xhv.value;
+	return ret;
+}