Adding upstream version 6.1.76.upstream/6.1.76

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 800 insertions, 0 deletions

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 000000000..0d8e6bd1c
--- /dev/null
+++ b/drivers/gpu/drm/xen/xen_drm_front.c
@@ -0,0 +1,800 @@
+// SPDX-License-Identifier: GPL-2.0 OR MIT
+
+/*
+ *  Xen para-virtual DRM device
+ *
+ * Copyright (C) 2016-2018 EPAM Systems Inc.
+ *
+ * Author: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
+ */
+
+#include <linux/delay.h>
+#include <linux/dma-mapping.h>
+#include <linux/module.h>
+#include <linux/of_device.h>
+
+#include <drm/drm_atomic_helper.h>
+#include <drm/drm_drv.h>
+#include <drm/drm_ioctl.h>
+#include <drm/drm_probe_helper.h>
+#include <drm/drm_file.h>
+#include <drm/drm_gem.h>
+
+#include <xen/platform_pci.h>
+#include <xen/xen.h>
+#include <xen/xenbus.h>
+
+#include <xen/xen-front-pgdir-shbuf.h>
+#include <xen/interface/io/displif.h>
+
+#include "xen_drm_front.h"
+#include "xen_drm_front_cfg.h"
+#include "xen_drm_front_evtchnl.h"
+#include "xen_drm_front_gem.h"
+#include "xen_drm_front_kms.h"
+
+struct xen_drm_front_dbuf {
+	struct list_head list;
+	u64 dbuf_cookie;
+	u64 fb_cookie;
+
+	struct xen_front_pgdir_shbuf shbuf;
+};
+
+static void dbuf_add_to_list(struct xen_drm_front_info *front_info,
+			     struct xen_drm_front_dbuf *dbuf, u64 dbuf_cookie)
+{
+	dbuf->dbuf_cookie = dbuf_cookie;
+	list_add(&dbuf->list, &front_info->dbuf_list);
+}
+
+static struct xen_drm_front_dbuf *dbuf_get(struct list_head *dbuf_list,
+					   u64 dbuf_cookie)
+{
+	struct xen_drm_front_dbuf *buf, *q;
+
+	list_for_each_entry_safe(buf, q, dbuf_list, list)
+		if (buf->dbuf_cookie == dbuf_cookie)
+			return buf;
+
+	return NULL;
+}
+
+static void dbuf_free(struct list_head *dbuf_list, u64 dbuf_cookie)
+{
+	struct xen_drm_front_dbuf *buf, *q;
+
+	list_for_each_entry_safe(buf, q, dbuf_list, list)
+		if (buf->dbuf_cookie == dbuf_cookie) {
+			list_del(&buf->list);
+			xen_front_pgdir_shbuf_unmap(&buf->shbuf);
+			xen_front_pgdir_shbuf_free(&buf->shbuf);
+			kfree(buf);
+			break;
+		}
+}
+
+static void dbuf_free_all(struct list_head *dbuf_list)
+{
+	struct xen_drm_front_dbuf *buf, *q;
+
+	list_for_each_entry_safe(buf, q, dbuf_list, list) {
+		list_del(&buf->list);
+		xen_front_pgdir_shbuf_unmap(&buf->shbuf);
+		xen_front_pgdir_shbuf_free(&buf->shbuf);
+		kfree(buf);
+	}
+}
+
+static struct xendispl_req *
+be_prepare_req(struct xen_drm_front_evtchnl *evtchnl, u8 operation)
+{
+	struct xendispl_req *req;
+
+	req = RING_GET_REQUEST(&evtchnl->u.req.ring,
+			       evtchnl->u.req.ring.req_prod_pvt);
+	req->operation = operation;
+	req->id = evtchnl->evt_next_id++;
+	evtchnl->evt_id = req->id;
+	return req;
+}
+
+static int be_stream_do_io(struct xen_drm_front_evtchnl *evtchnl,
+			   struct xendispl_req *req)
+{
+	reinit_completion(&evtchnl->u.req.completion);
+	if (unlikely(evtchnl->state != EVTCHNL_STATE_CONNECTED))
+		return -EIO;
+
+	xen_drm_front_evtchnl_flush(evtchnl);
+	return 0;
+}
+
+static int be_stream_wait_io(struct xen_drm_front_evtchnl *evtchnl)
+{
+	if (wait_for_completion_timeout(&evtchnl->u.req.completion,
+			msecs_to_jiffies(XEN_DRM_FRONT_WAIT_BACK_MS)) <= 0)
+		return -ETIMEDOUT;
+
+	return evtchnl->u.req.resp_status;
+}
+
+int xen_drm_front_mode_set(struct xen_drm_front_drm_pipeline *pipeline,
+			   u32 x, u32 y, u32 width, u32 height,
+			   u32 bpp, u64 fb_cookie)
+{
+	struct xen_drm_front_evtchnl *evtchnl;
+	struct xen_drm_front_info *front_info;
+	struct xendispl_req *req;
+	unsigned long flags;
+	int ret;
+
+	front_info = pipeline->drm_info->front_info;
+	evtchnl = &front_info->evt_pairs[pipeline->index].req;
+	if (unlikely(!evtchnl))
+		return -EIO;
+
+	mutex_lock(&evtchnl->u.req.req_io_lock);
+
+	spin_lock_irqsave(&front_info->io_lock, flags);
+	req = be_prepare_req(evtchnl, XENDISPL_OP_SET_CONFIG);
+	req->op.set_config.x = x;
+	req->op.set_config.y = y;
+	req->op.set_config.width = width;
+	req->op.set_config.height = height;
+	req->op.set_config.bpp = bpp;
+	req->op.set_config.fb_cookie = fb_cookie;
+
+	ret = be_stream_do_io(evtchnl, req);
+	spin_unlock_irqrestore(&front_info->io_lock, flags);
+
+	if (ret == 0)
+		ret = be_stream_wait_io(evtchnl);
+
+	mutex_unlock(&evtchnl->u.req.req_io_lock);
+	return ret;
+}
+
+int xen_drm_front_dbuf_create(struct xen_drm_front_info *front_info,
+			      u64 dbuf_cookie, u32 width, u32 height,
+			      u32 bpp, u64 size, u32 offset,
+			      struct page **pages)
+{
+	struct xen_drm_front_evtchnl *evtchnl;
+	struct xen_drm_front_dbuf *dbuf;
+	struct xendispl_req *req;
+	struct xen_front_pgdir_shbuf_cfg buf_cfg;
+	unsigned long flags;
+	int ret;
+
+	evtchnl = &front_info->evt_pairs[GENERIC_OP_EVT_CHNL].req;
+	if (unlikely(!evtchnl))
+		return -EIO;
+
+	dbuf = kzalloc(sizeof(*dbuf), GFP_KERNEL);
+	if (!dbuf)
+		return -ENOMEM;
+
+	dbuf_add_to_list(front_info, dbuf, dbuf_cookie);
+
+	memset(&buf_cfg, 0, sizeof(buf_cfg));
+	buf_cfg.xb_dev = front_info->xb_dev;
+	buf_cfg.num_pages = DIV_ROUND_UP(size, PAGE_SIZE);
+	buf_cfg.pages = pages;
+	buf_cfg.pgdir = &dbuf->shbuf;
+	buf_cfg.be_alloc = front_info->cfg.be_alloc;
+
+	ret = xen_front_pgdir_shbuf_alloc(&buf_cfg);
+	if (ret < 0)
+		goto fail_shbuf_alloc;
+
+	mutex_lock(&evtchnl->u.req.req_io_lock);
+
+	spin_lock_irqsave(&front_info->io_lock, flags);
+	req = be_prepare_req(evtchnl, XENDISPL_OP_DBUF_CREATE);
+	req->op.dbuf_create.gref_directory =
+			xen_front_pgdir_shbuf_get_dir_start(&dbuf->shbuf);
+	req->op.dbuf_create.buffer_sz = size;
+	req->op.dbuf_create.data_ofs = offset;
+	req->op.dbuf_create.dbuf_cookie = dbuf_cookie;
+	req->op.dbuf_create.width = width;
+	req->op.dbuf_create.height = height;
+	req->op.dbuf_create.bpp = bpp;
+	if (buf_cfg.be_alloc)
+		req->op.dbuf_create.flags |= XENDISPL_DBUF_FLG_REQ_ALLOC;
+
+	ret = be_stream_do_io(evtchnl, req);
+	spin_unlock_irqrestore(&front_info->io_lock, flags);
+
+	if (ret < 0)
+		goto fail;
+
+	ret = be_stream_wait_io(evtchnl);
+	if (ret < 0)
+		goto fail;
+
+	ret = xen_front_pgdir_shbuf_map(&dbuf->shbuf);
+	if (ret < 0)
+		goto fail;
+
+	mutex_unlock(&evtchnl->u.req.req_io_lock);
+	return 0;
+
+fail:
+	mutex_unlock(&evtchnl->u.req.req_io_lock);
+fail_shbuf_alloc:
+	dbuf_free(&front_info->dbuf_list, dbuf_cookie);
+	return ret;
+}
+
+static int xen_drm_front_dbuf_destroy(struct xen_drm_front_info *front_info,
+				      u64 dbuf_cookie)
+{
+	struct xen_drm_front_evtchnl *evtchnl;
+	struct xendispl_req *req;
+	unsigned long flags;
+	bool be_alloc;
+	int ret;
+
+	evtchnl = &front_info->evt_pairs[GENERIC_OP_EVT_CHNL].req;
+	if (unlikely(!evtchnl))
+		return -EIO;
+
+	be_alloc = front_info->cfg.be_alloc;
+
+	/*
+	 * For the backend allocated buffer release references now, so backend
+	 * can free the buffer.
+	 */
+	if (be_alloc)
+		dbuf_free(&front_info->dbuf_list, dbuf_cookie);
+
+	mutex_lock(&evtchnl->u.req.req_io_lock);
+
+	spin_lock_irqsave(&front_info->io_lock, flags);
+	req = be_prepare_req(evtchnl, XENDISPL_OP_DBUF_DESTROY);
+	req->op.dbuf_destroy.dbuf_cookie = dbuf_cookie;
+
+	ret = be_stream_do_io(evtchnl, req);
+	spin_unlock_irqrestore(&front_info->io_lock, flags);
+
+	if (ret == 0)
+		ret = be_stream_wait_io(evtchnl);
+
+	/*
+	 * Do this regardless of communication status with the backend:
+	 * if we cannot remove remote resources remove what we can locally.
+	 */
+	if (!be_alloc)
+		dbuf_free(&front_info->dbuf_list, dbuf_cookie);
+
+	mutex_unlock(&evtchnl->u.req.req_io_lock);
+	return ret;
+}
+
+int xen_drm_front_fb_attach(struct xen_drm_front_info *front_info,
+			    u64 dbuf_cookie, u64 fb_cookie, u32 width,
+			    u32 height, u32 pixel_format)
+{
+	struct xen_drm_front_evtchnl *evtchnl;
+	struct xen_drm_front_dbuf *buf;
+	struct xendispl_req *req;
+	unsigned long flags;
+	int ret;
+
+	evtchnl = &front_info->evt_pairs[GENERIC_OP_EVT_CHNL].req;
+	if (unlikely(!evtchnl))
+		return -EIO;
+
+	buf = dbuf_get(&front_info->dbuf_list, dbuf_cookie);
+	if (!buf)
+		return -EINVAL;
+
+	buf->fb_cookie = fb_cookie;
+
+	mutex_lock(&evtchnl->u.req.req_io_lock);
+
+	spin_lock_irqsave(&front_info->io_lock, flags);
+	req = be_prepare_req(evtchnl, XENDISPL_OP_FB_ATTACH);
+	req->op.fb_attach.dbuf_cookie = dbuf_cookie;
+	req->op.fb_attach.fb_cookie = fb_cookie;
+	req->op.fb_attach.width = width;
+	req->op.fb_attach.height = height;
+	req->op.fb_attach.pixel_format = pixel_format;
+
+	ret = be_stream_do_io(evtchnl, req);
+	spin_unlock_irqrestore(&front_info->io_lock, flags);
+
+	if (ret == 0)
+		ret = be_stream_wait_io(evtchnl);
+
+	mutex_unlock(&evtchnl->u.req.req_io_lock);
+	return ret;
+}
+
+int xen_drm_front_fb_detach(struct xen_drm_front_info *front_info,
+			    u64 fb_cookie)
+{
+	struct xen_drm_front_evtchnl *evtchnl;
+	struct xendispl_req *req;
+	unsigned long flags;
+	int ret;
+
+	evtchnl = &front_info->evt_pairs[GENERIC_OP_EVT_CHNL].req;
+	if (unlikely(!evtchnl))
+		return -EIO;
+
+	mutex_lock(&evtchnl->u.req.req_io_lock);
+
+	spin_lock_irqsave(&front_info->io_lock, flags);
+	req = be_prepare_req(evtchnl, XENDISPL_OP_FB_DETACH);
+	req->op.fb_detach.fb_cookie = fb_cookie;
+
+	ret = be_stream_do_io(evtchnl, req);
+	spin_unlock_irqrestore(&front_info->io_lock, flags);
+
+	if (ret == 0)
+		ret = be_stream_wait_io(evtchnl);
+
+	mutex_unlock(&evtchnl->u.req.req_io_lock);
+	return ret;
+}
+
+int xen_drm_front_page_flip(struct xen_drm_front_info *front_info,
+			    int conn_idx, u64 fb_cookie)
+{
+	struct xen_drm_front_evtchnl *evtchnl;
+	struct xendispl_req *req;
+	unsigned long flags;
+	int ret;
+
+	if (unlikely(conn_idx >= front_info->num_evt_pairs))
+		return -EINVAL;
+
+	evtchnl = &front_info->evt_pairs[conn_idx].req;
+
+	mutex_lock(&evtchnl->u.req.req_io_lock);
+
+	spin_lock_irqsave(&front_info->io_lock, flags);
+	req = be_prepare_req(evtchnl, XENDISPL_OP_PG_FLIP);
+	req->op.pg_flip.fb_cookie = fb_cookie;
+
+	ret = be_stream_do_io(evtchnl, req);
+	spin_unlock_irqrestore(&front_info->io_lock, flags);
+
+	if (ret == 0)
+		ret = be_stream_wait_io(evtchnl);
+
+	mutex_unlock(&evtchnl->u.req.req_io_lock);
+	return ret;
+}
+
+void xen_drm_front_on_frame_done(struct xen_drm_front_info *front_info,
+				 int conn_idx, u64 fb_cookie)
+{
+	struct xen_drm_front_drm_info *drm_info = front_info->drm_info;
+
+	if (unlikely(conn_idx >= front_info->cfg.num_connectors))
+		return;
+
+	xen_drm_front_kms_on_frame_done(&drm_info->pipeline[conn_idx],
+					fb_cookie);
+}
+
+void xen_drm_front_gem_object_free(struct drm_gem_object *obj)
+{
+	struct xen_drm_front_drm_info *drm_info = obj->dev->dev_private;
+	int idx;
+
+	if (drm_dev_enter(obj->dev, &idx)) {
+		xen_drm_front_dbuf_destroy(drm_info->front_info,
+					   xen_drm_front_dbuf_to_cookie(obj));
+		drm_dev_exit(idx);
+	} else {
+		dbuf_free(&drm_info->front_info->dbuf_list,
+			  xen_drm_front_dbuf_to_cookie(obj));
+	}
+
+	xen_drm_front_gem_free_object_unlocked(obj);
+}
+
+static int xen_drm_drv_dumb_create(struct drm_file *filp,
+				   struct drm_device *dev,
+				   struct drm_mode_create_dumb *args)
+{
+	struct xen_drm_front_drm_info *drm_info = dev->dev_private;
+	struct drm_gem_object *obj;
+	int ret;
+
+	/*
+	 * Dumb creation is a two stage process: first we create a fully
+	 * constructed GEM object which is communicated to the backend, and
+	 * only after that we can create GEM's handle. This is done so,
+	 * because of the possible races: once you create a handle it becomes
+	 * immediately visible to user-space, so the latter can try accessing
+	 * object without pages etc.
+	 * For details also see drm_gem_handle_create
+	 */
+	args->pitch = DIV_ROUND_UP(args->width * args->bpp, 8);
+	args->size = args->pitch * args->height;
+
+	obj = xen_drm_front_gem_create(dev, args->size);
+	if (IS_ERR(obj)) {
+		ret = PTR_ERR(obj);
+		goto fail;
+	}
+
+	ret = xen_drm_front_dbuf_create(drm_info->front_info,
+					xen_drm_front_dbuf_to_cookie(obj),
+					args->width, args->height, args->bpp,
+					args->size, 0,
+					xen_drm_front_gem_get_pages(obj));
+	if (ret)
+		goto fail_backend;
+
+	/* This is the tail of GEM object creation */
+	ret = drm_gem_handle_create(filp, obj, &args->handle);
+	if (ret)
+		goto fail_handle;
+
+	/* Drop reference from allocate - handle holds it now */
+	drm_gem_object_put(obj);
+	return 0;
+
+fail_handle:
+	xen_drm_front_dbuf_destroy(drm_info->front_info,
+				   xen_drm_front_dbuf_to_cookie(obj));
+fail_backend:
+	/* drop reference from allocate */
+	drm_gem_object_put(obj);
+fail:
+	DRM_ERROR("Failed to create dumb buffer: %d\n", ret);
+	return ret;
+}
+
+static void xen_drm_drv_release(struct drm_device *dev)
+{
+	struct xen_drm_front_drm_info *drm_info = dev->dev_private;
+	struct xen_drm_front_info *front_info = drm_info->front_info;
+
+	xen_drm_front_kms_fini(drm_info);
+
+	drm_atomic_helper_shutdown(dev);
+	drm_mode_config_cleanup(dev);
+
+	if (front_info->cfg.be_alloc)
+		xenbus_switch_state(front_info->xb_dev,
+				    XenbusStateInitialising);
+
+	kfree(drm_info);
+}
+
+DEFINE_DRM_GEM_FOPS(xen_drm_dev_fops);
+
+static const struct drm_driver xen_drm_driver = {
+	.driver_features           = DRIVER_GEM | DRIVER_MODESET | DRIVER_ATOMIC,
+	.release                   = xen_drm_drv_release,
+	.prime_handle_to_fd        = drm_gem_prime_handle_to_fd,
+	.prime_fd_to_handle        = drm_gem_prime_fd_to_handle,
+	.gem_prime_import_sg_table = xen_drm_front_gem_import_sg_table,
+	.gem_prime_mmap            = drm_gem_prime_mmap,
+	.dumb_create               = xen_drm_drv_dumb_create,
+	.fops                      = &xen_drm_dev_fops,
+	.name                      = "xendrm-du",
+	.desc                      = "Xen PV DRM Display Unit",
+	.date                      = "20180221",
+	.major                     = 1,
+	.minor                     = 0,
+
+};
+
+static int xen_drm_drv_init(struct xen_drm_front_info *front_info)
+{
+	struct device *dev = &front_info->xb_dev->dev;
+	struct xen_drm_front_drm_info *drm_info;
+	struct drm_device *drm_dev;
+	int ret;
+
+	if (drm_firmware_drivers_only())
+		return -ENODEV;
+
+	DRM_INFO("Creating %s\n", xen_drm_driver.desc);
+
+	drm_info = kzalloc(sizeof(*drm_info), GFP_KERNEL);
+	if (!drm_info) {
+		ret = -ENOMEM;
+		goto fail;
+	}
+
+	drm_info->front_info = front_info;
+	front_info->drm_info = drm_info;
+
+	drm_dev = drm_dev_alloc(&xen_drm_driver, dev);
+	if (IS_ERR(drm_dev)) {
+		ret = PTR_ERR(drm_dev);
+		goto fail_dev;
+	}
+
+	drm_info->drm_dev = drm_dev;
+
+	drm_dev->dev_private = drm_info;
+
+	ret = xen_drm_front_kms_init(drm_info);
+	if (ret) {
+		DRM_ERROR("Failed to initialize DRM/KMS, ret %d\n", ret);
+		goto fail_modeset;
+	}
+
+	ret = drm_dev_register(drm_dev, 0);
+	if (ret)
+		goto fail_register;
+
+	DRM_INFO("Initialized %s %d.%d.%d %s on minor %d\n",
+		 xen_drm_driver.name, xen_drm_driver.major,
+		 xen_drm_driver.minor, xen_drm_driver.patchlevel,
+		 xen_drm_driver.date, drm_dev->primary->index);
+
+	return 0;
+
+fail_register:
+	drm_dev_unregister(drm_dev);
+fail_modeset:
+	drm_kms_helper_poll_fini(drm_dev);
+	drm_mode_config_cleanup(drm_dev);
+	drm_dev_put(drm_dev);
+fail_dev:
+	kfree(drm_info);
+	front_info->drm_info = NULL;
+fail:
+	return ret;
+}
+
+static void xen_drm_drv_fini(struct xen_drm_front_info *front_info)
+{
+	struct xen_drm_front_drm_info *drm_info = front_info->drm_info;
+	struct drm_device *dev;
+
+	if (!drm_info)
+		return;
+
+	dev = drm_info->drm_dev;
+	if (!dev)
+		return;
+
+	/* Nothing to do if device is already unplugged */
+	if (drm_dev_is_unplugged(dev))
+		return;
+
+	drm_kms_helper_poll_fini(dev);
+	drm_dev_unplug(dev);
+	drm_dev_put(dev);
+
+	front_info->drm_info = NULL;
+
+	xen_drm_front_evtchnl_free_all(front_info);
+	dbuf_free_all(&front_info->dbuf_list);
+
+	/*
+	 * If we are not using backend allocated buffers, then tell the
+	 * backend we are ready to (re)initialize. Otherwise, wait for
+	 * drm_driver.release.
+	 */
+	if (!front_info->cfg.be_alloc)
+		xenbus_switch_state(front_info->xb_dev,
+				    XenbusStateInitialising);
+}
+
+static int displback_initwait(struct xen_drm_front_info *front_info)
+{
+	struct xen_drm_front_cfg *cfg = &front_info->cfg;
+	int ret;
+
+	cfg->front_info = front_info;
+	ret = xen_drm_front_cfg_card(front_info, cfg);
+	if (ret < 0)
+		return ret;
+
+	DRM_INFO("Have %d connector(s)\n", cfg->num_connectors);
+	/* Create event channels for all connectors and publish */
+	ret = xen_drm_front_evtchnl_create_all(front_info);
+	if (ret < 0)
+		return ret;
+
+	return xen_drm_front_evtchnl_publish_all(front_info);
+}
+
+static int displback_connect(struct xen_drm_front_info *front_info)
+{
+	xen_drm_front_evtchnl_set_state(front_info, EVTCHNL_STATE_CONNECTED);
+	return xen_drm_drv_init(front_info);
+}
+
+static void displback_disconnect(struct xen_drm_front_info *front_info)
+{
+	if (!front_info->drm_info)
+		return;
+
+	/* Tell the backend to wait until we release the DRM driver. */
+	xenbus_switch_state(front_info->xb_dev, XenbusStateReconfiguring);
+
+	xen_drm_drv_fini(front_info);
+}
+
+static void displback_changed(struct xenbus_device *xb_dev,
+			      enum xenbus_state backend_state)
+{
+	struct xen_drm_front_info *front_info = dev_get_drvdata(&xb_dev->dev);
+	int ret;
+
+	DRM_DEBUG("Backend state is %s, front is %s\n",
+		  xenbus_strstate(backend_state),
+		  xenbus_strstate(xb_dev->state));
+
+	switch (backend_state) {
+	case XenbusStateReconfiguring:
+	case XenbusStateReconfigured:
+	case XenbusStateInitialised:
+		break;
+
+	case XenbusStateInitialising:
+		if (xb_dev->state == XenbusStateReconfiguring)
+			break;
+
+		/* recovering after backend unexpected closure */
+		displback_disconnect(front_info);
+		break;
+
+	case XenbusStateInitWait:
+		if (xb_dev->state == XenbusStateReconfiguring)
+			break;
+
+		/* recovering after backend unexpected closure */
+		displback_disconnect(front_info);
+		if (xb_dev->state != XenbusStateInitialising)
+			break;
+
+		ret = displback_initwait(front_info);
+		if (ret < 0)
+			xenbus_dev_fatal(xb_dev, ret, "initializing frontend");
+		else
+			xenbus_switch_state(xb_dev, XenbusStateInitialised);
+		break;
+
+	case XenbusStateConnected:
+		if (xb_dev->state != XenbusStateInitialised)
+			break;
+
+		ret = displback_connect(front_info);
+		if (ret < 0) {
+			displback_disconnect(front_info);
+			xenbus_dev_fatal(xb_dev, ret, "connecting backend");
+		} else {
+			xenbus_switch_state(xb_dev, XenbusStateConnected);
+		}
+		break;
+
+	case XenbusStateClosing:
+		/*
+		 * in this state backend starts freeing resources,
+		 * so let it go into closed state, so we can also
+		 * remove ours
+		 */
+		break;
+
+	case XenbusStateUnknown:
+	case XenbusStateClosed:
+		if (xb_dev->state == XenbusStateClosed)
+			break;
+
+		displback_disconnect(front_info);
+		break;
+	}
+}
+
+static int xen_drv_probe(struct xenbus_device *xb_dev,
+			 const struct xenbus_device_id *id)
+{
+	struct xen_drm_front_info *front_info;
+	struct device *dev = &xb_dev->dev;
+	int ret;
+
+	ret = dma_coerce_mask_and_coherent(dev, DMA_BIT_MASK(64));
+	if (ret < 0) {
+		DRM_ERROR("Cannot setup DMA mask, ret %d", ret);
+		return ret;
+	}
+
+	front_info = devm_kzalloc(&xb_dev->dev,
+				  sizeof(*front_info), GFP_KERNEL);
+	if (!front_info)
+		return -ENOMEM;
+
+	front_info->xb_dev = xb_dev;
+	spin_lock_init(&front_info->io_lock);
+	INIT_LIST_HEAD(&front_info->dbuf_list);
+	dev_set_drvdata(&xb_dev->dev, front_info);
+
+	return xenbus_switch_state(xb_dev, XenbusStateInitialising);
+}
+
+static int xen_drv_remove(struct xenbus_device *dev)
+{
+	struct xen_drm_front_info *front_info = dev_get_drvdata(&dev->dev);
+	int to = 100;
+
+	xenbus_switch_state(dev, XenbusStateClosing);
+
+	/*
+	 * On driver removal it is disconnected from XenBus,
+	 * so no backend state change events come via .otherend_changed
+	 * callback. This prevents us from exiting gracefully, e.g.
+	 * signaling the backend to free event channels, waiting for its
+	 * state to change to XenbusStateClosed and cleaning at our end.
+	 * Normally when front driver removed backend will finally go into
+	 * XenbusStateInitWait state.
+	 *
+	 * Workaround: read backend's state manually and wait with time-out.
+	 */
+	while ((xenbus_read_unsigned(front_info->xb_dev->otherend, "state",
+				     XenbusStateUnknown) != XenbusStateInitWait) &&
+				     --to)
+		msleep(10);
+
+	if (!to) {
+		unsigned int state;
+
+		state = xenbus_read_unsigned(front_info->xb_dev->otherend,
+					     "state", XenbusStateUnknown);
+		DRM_ERROR("Backend state is %s while removing driver\n",
+			  xenbus_strstate(state));
+	}
+
+	xen_drm_drv_fini(front_info);
+	xenbus_frontend_closed(dev);
+	return 0;
+}
+
+static const struct xenbus_device_id xen_driver_ids[] = {
+	{ XENDISPL_DRIVER_NAME },
+	{ "" }
+};
+
+static struct xenbus_driver xen_driver = {
+	.ids = xen_driver_ids,
+	.probe = xen_drv_probe,
+	.remove = xen_drv_remove,
+	.otherend_changed = displback_changed,
+	.not_essential = true,
+};
+
+static int __init xen_drv_init(void)
+{
+	/* At the moment we only support case with XEN_PAGE_SIZE == PAGE_SIZE */
+	if (XEN_PAGE_SIZE != PAGE_SIZE) {
+		DRM_ERROR(XENDISPL_DRIVER_NAME ": different kernel and Xen page sizes are not supported: XEN_PAGE_SIZE (%lu) != PAGE_SIZE (%lu)\n",
+			  XEN_PAGE_SIZE, PAGE_SIZE);
+		return -ENODEV;
+	}
+
+	if (!xen_domain())
+		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_fini(void)
+{
+	DRM_INFO("Unregistering XEN PV " XENDISPL_DRIVER_NAME "\n");
+	xenbus_unregister_driver(&xen_driver);
+}
+
+module_init(xen_drv_init);
+module_exit(xen_drv_fini);
+
+MODULE_DESCRIPTION("Xen para-virtualized display device frontend");
+MODULE_LICENSE("GPL");
+MODULE_ALIAS("xen:" XENDISPL_DRIVER_NAME);