[PATCH 1/9] drm/xen-front: Introduce Xen para-virtualized frontend driver

[Oleksandr Andrushchenko <andr2000@gmail.com>]

From: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>

Introduce skeleton of the para-virtualized Xen display
frontend driver. This patch only adds required
essential stubs.

Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
---
 drivers/gpu/drm/Kconfig             |  2 +
 drivers/gpu/drm/Makefile            |  1 +
 drivers/gpu/drm/xen/Kconfig         | 17 ++++++++
 drivers/gpu/drm/xen/Makefile        |  5 +++
 drivers/gpu/drm/xen/xen_drm_front.c | 83 +++++++++++++++++++++++++++++++++++++
 5 files changed, 108 insertions(+)
 create mode 100644 drivers/gpu/drm/xen/Kconfig
 create mode 100644 drivers/gpu/drm/xen/Makefile
 create mode 100644 drivers/gpu/drm/xen/xen_drm_front.c

diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig
index deeefa7a1773..757825ac60df 100644
--- a/drivers/gpu/drm/Kconfig
+++ b/drivers/gpu/drm/Kconfig
@@ -289,6 +289,8 @@ source "drivers/gpu/drm/pl111/Kconfig"
 
 source "drivers/gpu/drm/tve200/Kconfig"
 
+source "drivers/gpu/drm/xen/Kconfig"
+
 # Keep legacy drivers last
 
 menuconfig DRM_LEGACY
diff --git a/drivers/gpu/drm/Makefile b/drivers/gpu/drm/Makefile
index 50093ff4479b..9d66657ea117 100644
--- a/drivers/gpu/drm/Makefile
+++ b/drivers/gpu/drm/Makefile
@@ -103,3 +103,4 @@ obj-$(CONFIG_DRM_MXSFB)	+= mxsfb/
 obj-$(CONFIG_DRM_TINYDRM) += tinydrm/
 obj-$(CONFIG_DRM_PL111) += pl111/
 obj-$(CONFIG_DRM_TVE200) += tve200/
+obj-$(CONFIG_DRM_XEN) += xen/
diff --git a/drivers/gpu/drm/xen/Kconfig b/drivers/gpu/drm/xen/Kconfig
new file mode 100644
index 000000000000..4cca160782ab
--- /dev/null
+++ b/drivers/gpu/drm/xen/Kconfig
@@ -0,0 +1,17 @@
+config DRM_XEN
+	bool "DRM Support for Xen guest OS"
+	depends on XEN
+	help
+	  Choose this option if you want to enable DRM support
+	  for Xen.
+
+config DRM_XEN_FRONTEND
+	tristate "Para-virtualized frontend driver for Xen guest OS"
+	depends on DRM_XEN
+	depends on DRM
+	select DRM_KMS_HELPER
+	select VIDEOMODE_HELPERS
+	select XEN_XENBUS_FRONTEND
+	help
+	  Choose this option if you want to enable a para-virtualized
+	  frontend DRM/KMS driver for Xen guest OSes.
diff --git a/drivers/gpu/drm/xen/Makefile b/drivers/gpu/drm/xen/Makefile
new file mode 100644
index 000000000000..967074d348f6
--- /dev/null
+++ b/drivers/gpu/drm/xen/Makefile
@@ -0,0 +1,5 @@
+# SPDX-License-Identifier: GPL-2.0
+
+drm_xen_front-objs := xen_drm_front.o
+
+obj-$(CONFIG_DRM_XEN_FRONTEND) += drm_xen_front.o
diff --git a/drivers/gpu/drm/xen/xen_drm_front.c b/drivers/gpu/drm/xen/xen_drm_front.c
new file mode 100644
index 000000000000..fd372fb464a1
--- /dev/null
+++ b/drivers/gpu/drm/xen/xen_drm_front.c
@@ -0,0 +1,83 @@
+/*
+ *  Xen para-virtual DRM device
+ *
+ *   This program is free software; you can redistribute it and/or modify
+ *   it under the terms of the GNU General Public License as published by
+ *   the Free Software Foundation; either version 2 of the License, or
+ *   (at your option) any later version.
+ *
+ *   This program is distributed in the hope that it will be useful,
+ *   but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *   GNU General Public License for more details.
+ *
+ * Copyright (C) 2016-2018 EPAM Systems Inc.
+ *
+ * Author: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
+ */
+
+#include <drm/drmP.h>
+
+#include <xen/platform_pci.h>
+#include <xen/xen.h>
+#include <xen/xenbus.h>
+
+#include <xen/interface/io/displif.h>
+
+static void backend_on_changed(struct xenbus_device *xb_dev,
+		enum xenbus_state backend_state)
+{
+}
+
+static int xen_drv_probe(struct xenbus_device *xb_dev,
+		const struct xenbus_device_id *id)
+{
+	return 0;
+}
+
+static int xen_drv_remove(struct xenbus_device *dev)
+{
+	return 0;
+}
+
+static const struct xenbus_device_id xen_drv_ids[] = {
+	{ XENDISPL_DRIVER_NAME },
+	{ "" }
+};
+
+static struct xenbus_driver xen_driver = {
+	.ids = xen_drv_ids,
+	.probe = xen_drv_probe,
+	.remove = xen_drv_remove,
+	.otherend_changed = backend_on_changed,
+};
+
+static int __init xen_drv_init(void)
+{
+	if (!xen_domain())
+		return -ENODEV;
+
+	if (xen_initial_domain()) {
+		DRM_ERROR(XENDISPL_DRIVER_NAME " cannot run in initial domain\n");
+		return -ENODEV;
+	}
+
+	if (!xen_has_pv_devices())
+		return -ENODEV;
+
+	DRM_INFO("Registering XEN PV " XENDISPL_DRIVER_NAME "\n");
+	return xenbus_register_frontend(&xen_driver);
+}
+
+static void __exit xen_drv_cleanup(void)
+{
+	DRM_INFO("Unregistering XEN PV " XENDISPL_DRIVER_NAME "\n");
+	xenbus_unregister_driver(&xen_driver);
+}
+
+module_init(xen_drv_init);
+module_exit(xen_drv_cleanup);
+
+MODULE_DESCRIPTION("Xen para-virtualized display device frontend");
+MODULE_LICENSE("GPL");
+MODULE_ALIAS("xen:"XENDISPL_DRIVER_NAME);
-- 
2.7.4