xref: /linux/drivers/gpu/drm/xen/xen_drm_front.c (revision 2da68a77) 
1 // SPDX-License-Identifier: GPL-2.0 OR MIT
2 
3 /*
4  *  Xen para-virtual DRM device
5  *
6  * Copyright (C) 2016-2018 EPAM Systems Inc.
7  *
8  * Author: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
9  */
10 
11 #include <linux/delay.h>
12 #include <linux/dma-mapping.h>
13 #include <linux/module.h>
14 #include <linux/of_device.h>
15 
16 #include <drm/drm_atomic_helper.h>
17 #include <drm/drm_drv.h>
18 #include <drm/drm_ioctl.h>
19 #include <drm/drm_probe_helper.h>
20 #include <drm/drm_file.h>
21 #include <drm/drm_gem.h>
22 
23 #include <xen/platform_pci.h>
24 #include <xen/xen.h>
25 #include <xen/xenbus.h>
26 
27 #include <xen/xen-front-pgdir-shbuf.h>
28 #include <xen/interface/io/displif.h>
29 
30 #include "xen_drm_front.h"
31 #include "xen_drm_front_cfg.h"
32 #include "xen_drm_front_evtchnl.h"
33 #include "xen_drm_front_gem.h"
34 #include "xen_drm_front_kms.h"
35 
36 struct xen_drm_front_dbuf {
37 	struct list_head list;
38 	u64 dbuf_cookie;
39 	u64 fb_cookie;
40 
41 	struct xen_front_pgdir_shbuf shbuf;
42 };
43 
44 static void dbuf_add_to_list(struct xen_drm_front_info *front_info,
45 			     struct xen_drm_front_dbuf *dbuf, u64 dbuf_cookie)
46 {
47 	dbuf->dbuf_cookie = dbuf_cookie;
48 	list_add(&dbuf->list, &front_info->dbuf_list);
49 }
50 
51 static struct xen_drm_front_dbuf *dbuf_get(struct list_head *dbuf_list,
52 					   u64 dbuf_cookie)
53 {
54 	struct xen_drm_front_dbuf *buf, *q;
55 
56 	list_for_each_entry_safe(buf, q, dbuf_list, list)
57 		if (buf->dbuf_cookie == dbuf_cookie)
58 			return buf;
59 
60 	return NULL;
61 }
62 
63 static void dbuf_free(struct list_head *dbuf_list, u64 dbuf_cookie)
64 {
65 	struct xen_drm_front_dbuf *buf, *q;
66 
67 	list_for_each_entry_safe(buf, q, dbuf_list, list)
68 		if (buf->dbuf_cookie == dbuf_cookie) {
69 			list_del(&buf->list);
70 			xen_front_pgdir_shbuf_unmap(&buf->shbuf);
71 			xen_front_pgdir_shbuf_free(&buf->shbuf);
72 			kfree(buf);
73 			break;
74 		}
75 }
76 
77 static void dbuf_free_all(struct list_head *dbuf_list)
78 {
79 	struct xen_drm_front_dbuf *buf, *q;
80 
81 	list_for_each_entry_safe(buf, q, dbuf_list, list) {
82 		list_del(&buf->list);
83 		xen_front_pgdir_shbuf_unmap(&buf->shbuf);
84 		xen_front_pgdir_shbuf_free(&buf->shbuf);
85 		kfree(buf);
86 	}
87 }
88 
89 static struct xendispl_req *
90 be_prepare_req(struct xen_drm_front_evtchnl *evtchnl, u8 operation)
91 {
92 	struct xendispl_req *req;
93 
94 	req = RING_GET_REQUEST(&evtchnl->u.req.ring,
95 			       evtchnl->u.req.ring.req_prod_pvt);
96 	req->operation = operation;
97 	req->id = evtchnl->evt_next_id++;
98 	evtchnl->evt_id = req->id;
99 	return req;
100 }
101 
102 static int be_stream_do_io(struct xen_drm_front_evtchnl *evtchnl,
103 			   struct xendispl_req *req)
104 {
105 	reinit_completion(&evtchnl->u.req.completion);
106 	if (unlikely(evtchnl->state != EVTCHNL_STATE_CONNECTED))
107 		return -EIO;
108 
109 	xen_drm_front_evtchnl_flush(evtchnl);
110 	return 0;
111 }
112 
113 static int be_stream_wait_io(struct xen_drm_front_evtchnl *evtchnl)
114 {
115 	if (wait_for_completion_timeout(&evtchnl->u.req.completion,
116 			msecs_to_jiffies(XEN_DRM_FRONT_WAIT_BACK_MS)) <= 0)
117 		return -ETIMEDOUT;
118 
119 	return evtchnl->u.req.resp_status;
120 }
121 
122 int xen_drm_front_mode_set(struct xen_drm_front_drm_pipeline *pipeline,
123 			   u32 x, u32 y, u32 width, u32 height,
124 			   u32 bpp, u64 fb_cookie)
125 {
126 	struct xen_drm_front_evtchnl *evtchnl;
127 	struct xen_drm_front_info *front_info;
128 	struct xendispl_req *req;
129 	unsigned long flags;
130 	int ret;
131 
132 	front_info = pipeline->drm_info->front_info;
133 	evtchnl = &front_info->evt_pairs[pipeline->index].req;
134 	if (unlikely(!evtchnl))
135 		return -EIO;
136 
137 	mutex_lock(&evtchnl->u.req.req_io_lock);
138 
139 	spin_lock_irqsave(&front_info->io_lock, flags);
140 	req = be_prepare_req(evtchnl, XENDISPL_OP_SET_CONFIG);
141 	req->op.set_config.x = x;
142 	req->op.set_config.y = y;
143 	req->op.set_config.width = width;
144 	req->op.set_config.height = height;
145 	req->op.set_config.bpp = bpp;
146 	req->op.set_config.fb_cookie = fb_cookie;
147 
148 	ret = be_stream_do_io(evtchnl, req);
149 	spin_unlock_irqrestore(&front_info->io_lock, flags);
150 
151 	if (ret == 0)
152 		ret = be_stream_wait_io(evtchnl);
153 
154 	mutex_unlock(&evtchnl->u.req.req_io_lock);
155 	return ret;
156 }
157 
158 int xen_drm_front_dbuf_create(struct xen_drm_front_info *front_info,
159 			      u64 dbuf_cookie, u32 width, u32 height,
160 			      u32 bpp, u64 size, u32 offset,
161 			      struct page **pages)
162 {
163 	struct xen_drm_front_evtchnl *evtchnl;
164 	struct xen_drm_front_dbuf *dbuf;
165 	struct xendispl_req *req;
166 	struct xen_front_pgdir_shbuf_cfg buf_cfg;
167 	unsigned long flags;
168 	int ret;
169 
170 	evtchnl = &front_info->evt_pairs[GENERIC_OP_EVT_CHNL].req;
171 	if (unlikely(!evtchnl))
172 		return -EIO;
173 
174 	dbuf = kzalloc(sizeof(*dbuf), GFP_KERNEL);
175 	if (!dbuf)
176 		return -ENOMEM;
177 
178 	dbuf_add_to_list(front_info, dbuf, dbuf_cookie);
179 
180 	memset(&buf_cfg, 0, sizeof(buf_cfg));
181 	buf_cfg.xb_dev = front_info->xb_dev;
182 	buf_cfg.num_pages = DIV_ROUND_UP(size, PAGE_SIZE);
183 	buf_cfg.pages = pages;
184 	buf_cfg.pgdir = &dbuf->shbuf;
185 	buf_cfg.be_alloc = front_info->cfg.be_alloc;
186 
187 	ret = xen_front_pgdir_shbuf_alloc(&buf_cfg);
188 	if (ret < 0)
189 		goto fail_shbuf_alloc;
190 
191 	mutex_lock(&evtchnl->u.req.req_io_lock);
192 
193 	spin_lock_irqsave(&front_info->io_lock, flags);
194 	req = be_prepare_req(evtchnl, XENDISPL_OP_DBUF_CREATE);
195 	req->op.dbuf_create.gref_directory =
196 			xen_front_pgdir_shbuf_get_dir_start(&dbuf->shbuf);
197 	req->op.dbuf_create.buffer_sz = size;
198 	req->op.dbuf_create.data_ofs = offset;
199 	req->op.dbuf_create.dbuf_cookie = dbuf_cookie;
200 	req->op.dbuf_create.width = width;
201 	req->op.dbuf_create.height = height;
202 	req->op.dbuf_create.bpp = bpp;
203 	if (buf_cfg.be_alloc)
204 		req->op.dbuf_create.flags |= XENDISPL_DBUF_FLG_REQ_ALLOC;
205 
206 	ret = be_stream_do_io(evtchnl, req);
207 	spin_unlock_irqrestore(&front_info->io_lock, flags);
208 
209 	if (ret < 0)
210 		goto fail;
211 
212 	ret = be_stream_wait_io(evtchnl);
213 	if (ret < 0)
214 		goto fail;
215 
216 	ret = xen_front_pgdir_shbuf_map(&dbuf->shbuf);
217 	if (ret < 0)
218 		goto fail;
219 
220 	mutex_unlock(&evtchnl->u.req.req_io_lock);
221 	return 0;
222 
223 fail:
224 	mutex_unlock(&evtchnl->u.req.req_io_lock);
225 fail_shbuf_alloc:
226 	dbuf_free(&front_info->dbuf_list, dbuf_cookie);
227 	return ret;
228 }
229 
230 static int xen_drm_front_dbuf_destroy(struct xen_drm_front_info *front_info,
231 				      u64 dbuf_cookie)
232 {
233 	struct xen_drm_front_evtchnl *evtchnl;
234 	struct xendispl_req *req;
235 	unsigned long flags;
236 	bool be_alloc;
237 	int ret;
238 
239 	evtchnl = &front_info->evt_pairs[GENERIC_OP_EVT_CHNL].req;
240 	if (unlikely(!evtchnl))
241 		return -EIO;
242 
243 	be_alloc = front_info->cfg.be_alloc;
244 
245 	/*
246 	 * For the backend allocated buffer release references now, so backend
247 	 * can free the buffer.
248 	 */
249 	if (be_alloc)
250 		dbuf_free(&front_info->dbuf_list, dbuf_cookie);
251 
252 	mutex_lock(&evtchnl->u.req.req_io_lock);
253 
254 	spin_lock_irqsave(&front_info->io_lock, flags);
255 	req = be_prepare_req(evtchnl, XENDISPL_OP_DBUF_DESTROY);
256 	req->op.dbuf_destroy.dbuf_cookie = dbuf_cookie;
257 
258 	ret = be_stream_do_io(evtchnl, req);
259 	spin_unlock_irqrestore(&front_info->io_lock, flags);
260 
261 	if (ret == 0)
262 		ret = be_stream_wait_io(evtchnl);
263 
264 	/*
265 	 * Do this regardless of communication status with the backend:
266 	 * if we cannot remove remote resources remove what we can locally.
267 	 */
268 	if (!be_alloc)
269 		dbuf_free(&front_info->dbuf_list, dbuf_cookie);
270 
271 	mutex_unlock(&evtchnl->u.req.req_io_lock);
272 	return ret;
273 }
274 
275 int xen_drm_front_fb_attach(struct xen_drm_front_info *front_info,
276 			    u64 dbuf_cookie, u64 fb_cookie, u32 width,
277 			    u32 height, u32 pixel_format)
278 {
279 	struct xen_drm_front_evtchnl *evtchnl;
280 	struct xen_drm_front_dbuf *buf;
281 	struct xendispl_req *req;
282 	unsigned long flags;
283 	int ret;
284 
285 	evtchnl = &front_info->evt_pairs[GENERIC_OP_EVT_CHNL].req;
286 	if (unlikely(!evtchnl))
287 		return -EIO;
288 
289 	buf = dbuf_get(&front_info->dbuf_list, dbuf_cookie);
290 	if (!buf)
291 		return -EINVAL;
292 
293 	buf->fb_cookie = fb_cookie;
294 
295 	mutex_lock(&evtchnl->u.req.req_io_lock);
296 
297 	spin_lock_irqsave(&front_info->io_lock, flags);
298 	req = be_prepare_req(evtchnl, XENDISPL_OP_FB_ATTACH);
299 	req->op.fb_attach.dbuf_cookie = dbuf_cookie;
300 	req->op.fb_attach.fb_cookie = fb_cookie;
301 	req->op.fb_attach.width = width;
302 	req->op.fb_attach.height = height;
303 	req->op.fb_attach.pixel_format = pixel_format;
304 
305 	ret = be_stream_do_io(evtchnl, req);
306 	spin_unlock_irqrestore(&front_info->io_lock, flags);
307 
308 	if (ret == 0)
309 		ret = be_stream_wait_io(evtchnl);
310 
311 	mutex_unlock(&evtchnl->u.req.req_io_lock);
312 	return ret;
313 }
314 
315 int xen_drm_front_fb_detach(struct xen_drm_front_info *front_info,
316 			    u64 fb_cookie)
317 {
318 	struct xen_drm_front_evtchnl *evtchnl;
319 	struct xendispl_req *req;
320 	unsigned long flags;
321 	int ret;
322 
323 	evtchnl = &front_info->evt_pairs[GENERIC_OP_EVT_CHNL].req;
324 	if (unlikely(!evtchnl))
325 		return -EIO;
326 
327 	mutex_lock(&evtchnl->u.req.req_io_lock);
328 
329 	spin_lock_irqsave(&front_info->io_lock, flags);
330 	req = be_prepare_req(evtchnl, XENDISPL_OP_FB_DETACH);
331 	req->op.fb_detach.fb_cookie = fb_cookie;
332 
333 	ret = be_stream_do_io(evtchnl, req);
334 	spin_unlock_irqrestore(&front_info->io_lock, flags);
335 
336 	if (ret == 0)
337 		ret = be_stream_wait_io(evtchnl);
338 
339 	mutex_unlock(&evtchnl->u.req.req_io_lock);
340 	return ret;
341 }
342 
343 int xen_drm_front_page_flip(struct xen_drm_front_info *front_info,
344 			    int conn_idx, u64 fb_cookie)
345 {
346 	struct xen_drm_front_evtchnl *evtchnl;
347 	struct xendispl_req *req;
348 	unsigned long flags;
349 	int ret;
350 
351 	if (unlikely(conn_idx >= front_info->num_evt_pairs))
352 		return -EINVAL;
353 
354 	evtchnl = &front_info->evt_pairs[conn_idx].req;
355 
356 	mutex_lock(&evtchnl->u.req.req_io_lock);
357 
358 	spin_lock_irqsave(&front_info->io_lock, flags);
359 	req = be_prepare_req(evtchnl, XENDISPL_OP_PG_FLIP);
360 	req->op.pg_flip.fb_cookie = fb_cookie;
361 
362 	ret = be_stream_do_io(evtchnl, req);
363 	spin_unlock_irqrestore(&front_info->io_lock, flags);
364 
365 	if (ret == 0)
366 		ret = be_stream_wait_io(evtchnl);
367 
368 	mutex_unlock(&evtchnl->u.req.req_io_lock);
369 	return ret;
370 }
371 
372 void xen_drm_front_on_frame_done(struct xen_drm_front_info *front_info,
373 				 int conn_idx, u64 fb_cookie)
374 {
375 	struct xen_drm_front_drm_info *drm_info = front_info->drm_info;
376 
377 	if (unlikely(conn_idx >= front_info->cfg.num_connectors))
378 		return;
379 
380 	xen_drm_front_kms_on_frame_done(&drm_info->pipeline[conn_idx],
381 					fb_cookie);
382 }
383 
384 void xen_drm_front_gem_object_free(struct drm_gem_object *obj)
385 {
386 	struct xen_drm_front_drm_info *drm_info = obj->dev->dev_private;
387 	int idx;
388 
389 	if (drm_dev_enter(obj->dev, &idx)) {
390 		xen_drm_front_dbuf_destroy(drm_info->front_info,
391 					   xen_drm_front_dbuf_to_cookie(obj));
392 		drm_dev_exit(idx);
393 	} else {
394 		dbuf_free(&drm_info->front_info->dbuf_list,
395 			  xen_drm_front_dbuf_to_cookie(obj));
396 	}
397 
398 	xen_drm_front_gem_free_object_unlocked(obj);
399 }
400 
401 static int xen_drm_drv_dumb_create(struct drm_file *filp,
402 				   struct drm_device *dev,
403 				   struct drm_mode_create_dumb *args)
404 {
405 	struct xen_drm_front_drm_info *drm_info = dev->dev_private;
406 	struct drm_gem_object *obj;
407 	int ret;
408 
409 	/*
410 	 * Dumb creation is a two stage process: first we create a fully
411 	 * constructed GEM object which is communicated to the backend, and
412 	 * only after that we can create GEM's handle. This is done so,
413 	 * because of the possible races: once you create a handle it becomes
414 	 * immediately visible to user-space, so the latter can try accessing
415 	 * object without pages etc.
416 	 * For details also see drm_gem_handle_create
417 	 */
418 	args->pitch = DIV_ROUND_UP(args->width * args->bpp, 8);
419 	args->size = args->pitch * args->height;
420 
421 	obj = xen_drm_front_gem_create(dev, args->size);
422 	if (IS_ERR(obj)) {
423 		ret = PTR_ERR(obj);
424 		goto fail;
425 	}
426 
427 	ret = xen_drm_front_dbuf_create(drm_info->front_info,
428 					xen_drm_front_dbuf_to_cookie(obj),
429 					args->width, args->height, args->bpp,
430 					args->size, 0,
431 					xen_drm_front_gem_get_pages(obj));
432 	if (ret)
433 		goto fail_backend;
434 
435 	/* This is the tail of GEM object creation */
436 	ret = drm_gem_handle_create(filp, obj, &args->handle);
437 	if (ret)
438 		goto fail_handle;
439 
440 	/* Drop reference from allocate - handle holds it now */
441 	drm_gem_object_put(obj);
442 	return 0;
443 
444 fail_handle:
445 	xen_drm_front_dbuf_destroy(drm_info->front_info,
446 				   xen_drm_front_dbuf_to_cookie(obj));
447 fail_backend:
448 	/* drop reference from allocate */
449 	drm_gem_object_put(obj);
450 fail:
451 	DRM_ERROR("Failed to create dumb buffer: %d\n", ret);
452 	return ret;
453 }
454 
455 static void xen_drm_drv_release(struct drm_device *dev)
456 {
457 	struct xen_drm_front_drm_info *drm_info = dev->dev_private;
458 	struct xen_drm_front_info *front_info = drm_info->front_info;
459 
460 	xen_drm_front_kms_fini(drm_info);
461 
462 	drm_atomic_helper_shutdown(dev);
463 	drm_mode_config_cleanup(dev);
464 
465 	if (front_info->cfg.be_alloc)
466 		xenbus_switch_state(front_info->xb_dev,
467 				    XenbusStateInitialising);
468 
469 	kfree(drm_info);
470 }
471 
472 DEFINE_DRM_GEM_FOPS(xen_drm_dev_fops);
473 
474 static const struct drm_driver xen_drm_driver = {
475 	.driver_features           = DRIVER_GEM | DRIVER_MODESET | DRIVER_ATOMIC,
476 	.release                   = xen_drm_drv_release,
477 	.prime_handle_to_fd        = drm_gem_prime_handle_to_fd,
478 	.prime_fd_to_handle        = drm_gem_prime_fd_to_handle,
479 	.gem_prime_import_sg_table = xen_drm_front_gem_import_sg_table,
480 	.gem_prime_mmap            = drm_gem_prime_mmap,
481 	.dumb_create               = xen_drm_drv_dumb_create,
482 	.fops                      = &xen_drm_dev_fops,
483 	.name                      = "xendrm-du",
484 	.desc                      = "Xen PV DRM Display Unit",
485 	.date                      = "20180221",
486 	.major                     = 1,
487 	.minor                     = 0,
488 
489 };
490 
491 static int xen_drm_drv_init(struct xen_drm_front_info *front_info)
492 {
493 	struct device *dev = &front_info->xb_dev->dev;
494 	struct xen_drm_front_drm_info *drm_info;
495 	struct drm_device *drm_dev;
496 	int ret;
497 
498 	if (drm_firmware_drivers_only())
499 		return -ENODEV;
500 
501 	DRM_INFO("Creating %s\n", xen_drm_driver.desc);
502 
503 	drm_info = kzalloc(sizeof(*drm_info), GFP_KERNEL);
504 	if (!drm_info) {
505 		ret = -ENOMEM;
506 		goto fail;
507 	}
508 
509 	drm_info->front_info = front_info;
510 	front_info->drm_info = drm_info;
511 
512 	drm_dev = drm_dev_alloc(&xen_drm_driver, dev);
513 	if (IS_ERR(drm_dev)) {
514 		ret = PTR_ERR(drm_dev);
515 		goto fail_dev;
516 	}
517 
518 	drm_info->drm_dev = drm_dev;
519 
520 	drm_dev->dev_private = drm_info;
521 
522 	ret = xen_drm_front_kms_init(drm_info);
523 	if (ret) {
524 		DRM_ERROR("Failed to initialize DRM/KMS, ret %d\n", ret);
525 		goto fail_modeset;
526 	}
527 
528 	ret = drm_dev_register(drm_dev, 0);
529 	if (ret)
530 		goto fail_register;
531 
532 	DRM_INFO("Initialized %s %d.%d.%d %s on minor %d\n",
533 		 xen_drm_driver.name, xen_drm_driver.major,
534 		 xen_drm_driver.minor, xen_drm_driver.patchlevel,
535 		 xen_drm_driver.date, drm_dev->primary->index);
536 
537 	return 0;
538 
539 fail_register:
540 	drm_dev_unregister(drm_dev);
541 fail_modeset:
542 	drm_kms_helper_poll_fini(drm_dev);
543 	drm_mode_config_cleanup(drm_dev);
544 	drm_dev_put(drm_dev);
545 fail_dev:
546 	kfree(drm_info);
547 	front_info->drm_info = NULL;
548 fail:
549 	return ret;
550 }
551 
552 static void xen_drm_drv_fini(struct xen_drm_front_info *front_info)
553 {
554 	struct xen_drm_front_drm_info *drm_info = front_info->drm_info;
555 	struct drm_device *dev;
556 
557 	if (!drm_info)
558 		return;
559 
560 	dev = drm_info->drm_dev;
561 	if (!dev)
562 		return;
563 
564 	/* Nothing to do if device is already unplugged */
565 	if (drm_dev_is_unplugged(dev))
566 		return;
567 
568 	drm_kms_helper_poll_fini(dev);
569 	drm_dev_unplug(dev);
570 	drm_dev_put(dev);
571 
572 	front_info->drm_info = NULL;
573 
574 	xen_drm_front_evtchnl_free_all(front_info);
575 	dbuf_free_all(&front_info->dbuf_list);
576 
577 	/*
578 	 * If we are not using backend allocated buffers, then tell the
579 	 * backend we are ready to (re)initialize. Otherwise, wait for
580 	 * drm_driver.release.
581 	 */
582 	if (!front_info->cfg.be_alloc)
583 		xenbus_switch_state(front_info->xb_dev,
584 				    XenbusStateInitialising);
585 }
586 
587 static int displback_initwait(struct xen_drm_front_info *front_info)
588 {
589 	struct xen_drm_front_cfg *cfg = &front_info->cfg;
590 	int ret;
591 
592 	cfg->front_info = front_info;
593 	ret = xen_drm_front_cfg_card(front_info, cfg);
594 	if (ret < 0)
595 		return ret;
596 
597 	DRM_INFO("Have %d connector(s)\n", cfg->num_connectors);
598 	/* Create event channels for all connectors and publish */
599 	ret = xen_drm_front_evtchnl_create_all(front_info);
600 	if (ret < 0)
601 		return ret;
602 
603 	return xen_drm_front_evtchnl_publish_all(front_info);
604 }
605 
606 static int displback_connect(struct xen_drm_front_info *front_info)
607 {
608 	xen_drm_front_evtchnl_set_state(front_info, EVTCHNL_STATE_CONNECTED);
609 	return xen_drm_drv_init(front_info);
610 }
611 
612 static void displback_disconnect(struct xen_drm_front_info *front_info)
613 {
614 	if (!front_info->drm_info)
615 		return;
616 
617 	/* Tell the backend to wait until we release the DRM driver. */
618 	xenbus_switch_state(front_info->xb_dev, XenbusStateReconfiguring);
619 
620 	xen_drm_drv_fini(front_info);
621 }
622 
623 static void displback_changed(struct xenbus_device *xb_dev,
624 			      enum xenbus_state backend_state)
625 {
626 	struct xen_drm_front_info *front_info = dev_get_drvdata(&xb_dev->dev);
627 	int ret;
628 
629 	DRM_DEBUG("Backend state is %s, front is %s\n",
630 		  xenbus_strstate(backend_state),
631 		  xenbus_strstate(xb_dev->state));
632 
633 	switch (backend_state) {
634 	case XenbusStateReconfiguring:
635 	case XenbusStateReconfigured:
636 	case XenbusStateInitialised:
637 		break;
638 
639 	case XenbusStateInitialising:
640 		if (xb_dev->state == XenbusStateReconfiguring)
641 			break;
642 
643 		/* recovering after backend unexpected closure */
644 		displback_disconnect(front_info);
645 		break;
646 
647 	case XenbusStateInitWait:
648 		if (xb_dev->state == XenbusStateReconfiguring)
649 			break;
650 
651 		/* recovering after backend unexpected closure */
652 		displback_disconnect(front_info);
653 		if (xb_dev->state != XenbusStateInitialising)
654 			break;
655 
656 		ret = displback_initwait(front_info);
657 		if (ret < 0)
658 			xenbus_dev_fatal(xb_dev, ret, "initializing frontend");
659 		else
660 			xenbus_switch_state(xb_dev, XenbusStateInitialised);
661 		break;
662 
663 	case XenbusStateConnected:
664 		if (xb_dev->state != XenbusStateInitialised)
665 			break;
666 
667 		ret = displback_connect(front_info);
668 		if (ret < 0) {
669 			displback_disconnect(front_info);
670 			xenbus_dev_fatal(xb_dev, ret, "connecting backend");
671 		} else {
672 			xenbus_switch_state(xb_dev, XenbusStateConnected);
673 		}
674 		break;
675 
676 	case XenbusStateClosing:
677 		/*
678 		 * in this state backend starts freeing resources,
679 		 * so let it go into closed state, so we can also
680 		 * remove ours
681 		 */
682 		break;
683 
684 	case XenbusStateUnknown:
685 	case XenbusStateClosed:
686 		if (xb_dev->state == XenbusStateClosed)
687 			break;
688 
689 		displback_disconnect(front_info);
690 		break;
691 	}
692 }
693 
694 static int xen_drv_probe(struct xenbus_device *xb_dev,
695 			 const struct xenbus_device_id *id)
696 {
697 	struct xen_drm_front_info *front_info;
698 	struct device *dev = &xb_dev->dev;
699 	int ret;
700 
701 	ret = dma_coerce_mask_and_coherent(dev, DMA_BIT_MASK(64));
702 	if (ret < 0) {
703 		DRM_ERROR("Cannot setup DMA mask, ret %d", ret);
704 		return ret;
705 	}
706 
707 	front_info = devm_kzalloc(&xb_dev->dev,
708 				  sizeof(*front_info), GFP_KERNEL);
709 	if (!front_info)
710 		return -ENOMEM;
711 
712 	front_info->xb_dev = xb_dev;
713 	spin_lock_init(&front_info->io_lock);
714 	INIT_LIST_HEAD(&front_info->dbuf_list);
715 	dev_set_drvdata(&xb_dev->dev, front_info);
716 
717 	return xenbus_switch_state(xb_dev, XenbusStateInitialising);
718 }
719 
720 static int xen_drv_remove(struct xenbus_device *dev)
721 {
722 	struct xen_drm_front_info *front_info = dev_get_drvdata(&dev->dev);
723 	int to = 100;
724 
725 	xenbus_switch_state(dev, XenbusStateClosing);
726 
727 	/*
728 	 * On driver removal it is disconnected from XenBus,
729 	 * so no backend state change events come via .otherend_changed
730 	 * callback. This prevents us from exiting gracefully, e.g.
731 	 * signaling the backend to free event channels, waiting for its
732 	 * state to change to XenbusStateClosed and cleaning at our end.
733 	 * Normally when front driver removed backend will finally go into
734 	 * XenbusStateInitWait state.
735 	 *
736 	 * Workaround: read backend's state manually and wait with time-out.
737 	 */
738 	while ((xenbus_read_unsigned(front_info->xb_dev->otherend, "state",
739 				     XenbusStateUnknown) != XenbusStateInitWait) &&
740 				     --to)
741 		msleep(10);
742 
743 	if (!to) {
744 		unsigned int state;
745 
746 		state = xenbus_read_unsigned(front_info->xb_dev->otherend,
747 					     "state", XenbusStateUnknown);
748 		DRM_ERROR("Backend state is %s while removing driver\n",
749 			  xenbus_strstate(state));
750 	}
751 
752 	xen_drm_drv_fini(front_info);
753 	xenbus_frontend_closed(dev);
754 	return 0;
755 }
756 
757 static const struct xenbus_device_id xen_driver_ids[] = {
758 	{ XENDISPL_DRIVER_NAME },
759 	{ "" }
760 };
761 
762 static struct xenbus_driver xen_driver = {
763 	.ids = xen_driver_ids,
764 	.probe = xen_drv_probe,
765 	.remove = xen_drv_remove,
766 	.otherend_changed = displback_changed,
767 	.not_essential = true,
768 };
769 
770 static int __init xen_drv_init(void)
771 {
772 	/* At the moment we only support case with XEN_PAGE_SIZE == PAGE_SIZE */
773 	if (XEN_PAGE_SIZE != PAGE_SIZE) {
774 		DRM_ERROR(XENDISPL_DRIVER_NAME ": different kernel and Xen page sizes are not supported: XEN_PAGE_SIZE (%lu) != PAGE_SIZE (%lu)\n",
775 			  XEN_PAGE_SIZE, PAGE_SIZE);
776 		return -ENODEV;
777 	}
778 
779 	if (!xen_domain())
780 		return -ENODEV;
781 
782 	if (!xen_has_pv_devices())
783 		return -ENODEV;
784 
785 	DRM_INFO("Registering XEN PV " XENDISPL_DRIVER_NAME "\n");
786 	return xenbus_register_frontend(&xen_driver);
787 }
788 
789 static void __exit xen_drv_fini(void)
790 {
791 	DRM_INFO("Unregistering XEN PV " XENDISPL_DRIVER_NAME "\n");
792 	xenbus_unregister_driver(&xen_driver);
793 }
794 
795 module_init(xen_drv_init);
796 module_exit(xen_drv_fini);
797 
798 MODULE_DESCRIPTION("Xen para-virtualized display device frontend");
799 MODULE_LICENSE("GPL");
800 MODULE_ALIAS("xen:" XENDISPL_DRIVER_NAME);
801