board: Introduce xenguest_arm64 board

Introduce a minimal Xen guest board running as a virtual
machine under Xen Project's hypervisor [1], [2].

Part of the code is ported from Xen mini-os and also uses
work initially done by different authors from NXP: please see
relevant files for their copyrights.

[1] https://xenbits.xen.org
[2] https://wiki.xenproject.org/

Signed-off-by: Andrii Anisov <andrii_anisov@epam.com>
Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
Signed-off-by: Anastasiia Lukianenko <anastasiia_lukianenko@epam.com>

arch/arm/cpu/armv8/Makefile

@@ -40,3 +40,4 @@ obj-$(CONFIG_TARGET_HIKEY) += hisilicon/
 obj-$(CONFIG_ARMV8_PSCI) += psci.o
 obj-$(CONFIG_ARCH_SUNXI) += lowlevel_init.o
 obj-$(CONFIG_TARGET_BCMNS3) += bcmns3/
+obj-$(CONFIG_XEN) += xen/

arch/arm/cpu/armv8/xen/Makefile

@@ -0,0 +1,6 @@
+# SPDX-License-Identifier: GPL-2.0+
+#
+# (C) 2018 NXP
+# (C) 2020 EPAM Systems Inc.
+
+obj-y += lowlevel_init.o hypercall.o

arch/arm/cpu/armv8/xen/hypercall.S

@@ -0,0 +1,79 @@
+/* SPDX-License-Identifier: GPL-2.0
+ *
+ * hypercall.S
+ *
+ * Xen hypercall wrappers
+ *
+ * Stefano Stabellini <stefano.stabellini@eu.citrix.com>, Citrix, 2012
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License version 2
+ * as published by the Free Software Foundation; or, when distributed
+ * separately from the Linux kernel or incorporated into other
+ * software packages, subject to the following license:
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this source file (the "Software"), to deal in the Software without
+ * restriction, including without limitation the rights to use, copy, modify,
+ * merge, publish, distribute, sublicense, and/or sell copies of the Software,
+ * and to permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
+ * IN THE SOFTWARE.
+ */
+
+/*
+ * The Xen hypercall calling convention is very similar to the procedure
+ * call standard for the ARM 64-bit architecture: the first parameter is
+ * passed in x0, the second in x1, the third in x2, the fourth in x3 and
+ * the fifth in x4.
+ *
+ * The hypercall number is passed in x16.
+ *
+ * The return value is in x0.
+ *
+ * The hvc ISS is required to be 0xEA1, that is the Xen specific ARM
+ * hypercall tag.
+ *
+ * Parameter structs passed to hypercalls are laid out according to
+ * the ARM 64-bit EABI standard.
+ */
+
+#include <xen/interface/xen.h>
+
+#define XEN_HYPERCALL_TAG	0xEA1
+
+#define HYPERCALL_SIMPLE(hypercall)		\
+.globl HYPERVISOR_##hypercall;                  \
+.align 4,0x90;                                  \
+HYPERVISOR_##hypercall:				\
+	mov x16, #__HYPERVISOR_##hypercall;	\
+	hvc XEN_HYPERCALL_TAG;			\
+	ret;					\
+
+#define HYPERCALL0 HYPERCALL_SIMPLE
+#define HYPERCALL1 HYPERCALL_SIMPLE
+#define HYPERCALL2 HYPERCALL_SIMPLE
+#define HYPERCALL3 HYPERCALL_SIMPLE
+#define HYPERCALL4 HYPERCALL_SIMPLE
+#define HYPERCALL5 HYPERCALL_SIMPLE
+
+                .text
+
+HYPERCALL2(xen_version);
+HYPERCALL3(console_io);
+HYPERCALL3(grant_table_op);
+HYPERCALL2(sched_op);
+HYPERCALL2(event_channel_op);
+HYPERCALL2(hvm_op);
+HYPERCALL2(memory_op);
+

arch/arm/cpu/armv8/xen/lowlevel_init.S

@@ -0,0 +1,33 @@
+/* SPDX-License-Identifier: GPL-2.0+
+ *
+ * (C) 2017 NXP
+ * (C) 2020 EPAM Systems Inc.
+ */
+
+#include <config.h>
+
+.align 8
+.global rom_pointer
+rom_pointer:
+	.space 32
+
+/*
+ * Routine: save_boot_params (called after reset from start.S)
+ */
+
+.global save_boot_params
+save_boot_params:
+	/* The firmware provided ATAG/FDT address can be found in r2/x0 */
+	adr	x1, rom_pointer
+	stp	x0, x2, [x1], #16
+	stp	x3, x4, [x1], #16
+
+	/* Returns */
+	b	save_boot_params_ret
+
+.global restore_boot_params
+restore_boot_params:
+	adr	x1, rom_pointer
+	ldp	x0, x2, [x1], #16
+	ldp	x3, x4, [x1], #16
+	ret