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 	DRM_INFO("Creating %s\n", xen_drm_driver.desc);
499 
500 	drm_info = kzalloc(sizeof(*drm_info), GFP_KERNEL);
501 	if (!drm_info) {
502 		ret = -ENOMEM;
503 		goto fail;
504 	}
505 
506 	drm_info->front_info = front_info;
507 	front_info->drm_info = drm_info;
508 
509 	drm_dev = drm_dev_alloc(&xen_drm_driver, dev);
510 	if (IS_ERR(drm_dev)) {
511 		ret = PTR_ERR(drm_dev);
512 		goto fail_dev;
513 	}
514 
515 	drm_info->drm_dev = drm_dev;
516 
517 	drm_dev->dev_private = drm_info;
518 
519 	ret = xen_drm_front_kms_init(drm_info);
520 	if (ret) {
521 		DRM_ERROR("Failed to initialize DRM/KMS, ret %d\n", ret);
522 		goto fail_modeset;
523 	}
524 
525 	ret = drm_dev_register(drm_dev, 0);
526 	if (ret)
527 		goto fail_register;
528 
529 	DRM_INFO("Initialized %s %d.%d.%d %s on minor %d\n",
530 		 xen_drm_driver.name, xen_drm_driver.major,
531 		 xen_drm_driver.minor, xen_drm_driver.patchlevel,
532 		 xen_drm_driver.date, drm_dev->primary->index);
533 
534 	return 0;
535 
536 fail_register:
537 	drm_dev_unregister(drm_dev);
538 fail_modeset:
539 	drm_kms_helper_poll_fini(drm_dev);
540 	drm_mode_config_cleanup(drm_dev);
541 	drm_dev_put(drm_dev);
542 fail_dev:
543 	kfree(drm_info);
544 	front_info->drm_info = NULL;
545 fail:
546 	return ret;
547 }
548 
549 static void xen_drm_drv_fini(struct xen_drm_front_info *front_info)
550 {
551 	struct xen_drm_front_drm_info *drm_info = front_info->drm_info;
552 	struct drm_device *dev;
553 
554 	if (!drm_info)
555 		return;
556 
557 	dev = drm_info->drm_dev;
558 	if (!dev)
559 		return;
560 
561 	/* Nothing to do if device is already unplugged */
562 	if (drm_dev_is_unplugged(dev))
563 		return;
564 
565 	drm_kms_helper_poll_fini(dev);
566 	drm_dev_unplug(dev);
567 	drm_dev_put(dev);
568 
569 	front_info->drm_info = NULL;
570 
571 	xen_drm_front_evtchnl_free_all(front_info);
572 	dbuf_free_all(&front_info->dbuf_list);
573 
574 	/*
575 	 * If we are not using backend allocated buffers, then tell the
576 	 * backend we are ready to (re)initialize. Otherwise, wait for
577 	 * drm_driver.release.
578 	 */
579 	if (!front_info->cfg.be_alloc)
580 		xenbus_switch_state(front_info->xb_dev,
581 				    XenbusStateInitialising);
582 }
583 
584 static int displback_initwait(struct xen_drm_front_info *front_info)
585 {
586 	struct xen_drm_front_cfg *cfg = &front_info->cfg;
587 	int ret;
588 
589 	cfg->front_info = front_info;
590 	ret = xen_drm_front_cfg_card(front_info, cfg);
591 	if (ret < 0)
592 		return ret;
593 
594 	DRM_INFO("Have %d connector(s)\n", cfg->num_connectors);
595 	/* Create event channels for all connectors and publish */
596 	ret = xen_drm_front_evtchnl_create_all(front_info);
597 	if (ret < 0)
598 		return ret;
599 
600 	return xen_drm_front_evtchnl_publish_all(front_info);
601 }
602 
603 static int displback_connect(struct xen_drm_front_info *front_info)
604 {
605 	xen_drm_front_evtchnl_set_state(front_info, EVTCHNL_STATE_CONNECTED);
606 	return xen_drm_drv_init(front_info);
607 }
608 
609 static void displback_disconnect(struct xen_drm_front_info *front_info)
610 {
611 	if (!front_info->drm_info)
612 		return;
613 
614 	/* Tell the backend to wait until we release the DRM driver. */
615 	xenbus_switch_state(front_info->xb_dev, XenbusStateReconfiguring);
616 
617 	xen_drm_drv_fini(front_info);
618 }
619 
620 static void displback_changed(struct xenbus_device *xb_dev,
621 			      enum xenbus_state backend_state)
622 {
623 	struct xen_drm_front_info *front_info = dev_get_drvdata(&xb_dev->dev);
624 	int ret;
625 
626 	DRM_DEBUG("Backend state is %s, front is %s\n",
627 		  xenbus_strstate(backend_state),
628 		  xenbus_strstate(xb_dev->state));
629 
630 	switch (backend_state) {
631 	case XenbusStateReconfiguring:
632 	case XenbusStateReconfigured:
633 	case XenbusStateInitialised:
634 		break;
635 
636 	case XenbusStateInitialising:
637 		if (xb_dev->state == XenbusStateReconfiguring)
638 			break;
639 
640 		/* recovering after backend unexpected closure */
641 		displback_disconnect(front_info);
642 		break;
643 
644 	case XenbusStateInitWait:
645 		if (xb_dev->state == XenbusStateReconfiguring)
646 			break;
647 
648 		/* recovering after backend unexpected closure */
649 		displback_disconnect(front_info);
650 		if (xb_dev->state != XenbusStateInitialising)
651 			break;
652 
653 		ret = displback_initwait(front_info);
654 		if (ret < 0)
655 			xenbus_dev_fatal(xb_dev, ret, "initializing frontend");
656 		else
657 			xenbus_switch_state(xb_dev, XenbusStateInitialised);
658 		break;
659 
660 	case XenbusStateConnected:
661 		if (xb_dev->state != XenbusStateInitialised)
662 			break;
663 
664 		ret = displback_connect(front_info);
665 		if (ret < 0) {
666 			displback_disconnect(front_info);
667 			xenbus_dev_fatal(xb_dev, ret, "connecting backend");
668 		} else {
669 			xenbus_switch_state(xb_dev, XenbusStateConnected);
670 		}
671 		break;
672 
673 	case XenbusStateClosing:
674 		/*
675 		 * in this state backend starts freeing resources,
676 		 * so let it go into closed state, so we can also
677 		 * remove ours
678 		 */
679 		break;
680 
681 	case XenbusStateUnknown:
682 	case XenbusStateClosed:
683 		if (xb_dev->state == XenbusStateClosed)
684 			break;
685 
686 		displback_disconnect(front_info);
687 		break;
688 	}
689 }
690 
691 static int xen_drv_probe(struct xenbus_device *xb_dev,
692 			 const struct xenbus_device_id *id)
693 {
694 	struct xen_drm_front_info *front_info;
695 	struct device *dev = &xb_dev->dev;
696 	int ret;
697 
698 	ret = dma_coerce_mask_and_coherent(dev, DMA_BIT_MASK(64));
699 	if (ret < 0) {
700 		DRM_ERROR("Cannot setup DMA mask, ret %d", ret);
701 		return ret;
702 	}
703 
704 	front_info = devm_kzalloc(&xb_dev->dev,
705 				  sizeof(*front_info), GFP_KERNEL);
706 	if (!front_info)
707 		return -ENOMEM;
708 
709 	front_info->xb_dev = xb_dev;
710 	spin_lock_init(&front_info->io_lock);
711 	INIT_LIST_HEAD(&front_info->dbuf_list);
712 	dev_set_drvdata(&xb_dev->dev, front_info);
713 
714 	return xenbus_switch_state(xb_dev, XenbusStateInitialising);
715 }
716 
717 static int xen_drv_remove(struct xenbus_device *dev)
718 {
719 	struct xen_drm_front_info *front_info = dev_get_drvdata(&dev->dev);
720 	int to = 100;
721 
722 	xenbus_switch_state(dev, XenbusStateClosing);
723 
724 	/*
725 	 * On driver removal it is disconnected from XenBus,
726 	 * so no backend state change events come via .otherend_changed
727 	 * callback. This prevents us from exiting gracefully, e.g.
728 	 * signaling the backend to free event channels, waiting for its
729 	 * state to change to XenbusStateClosed and cleaning at our end.
730 	 * Normally when front driver removed backend will finally go into
731 	 * XenbusStateInitWait state.
732 	 *
733 	 * Workaround: read backend's state manually and wait with time-out.
734 	 */
735 	while ((xenbus_read_unsigned(front_info->xb_dev->otherend, "state",
736 				     XenbusStateUnknown) != XenbusStateInitWait) &&
737 				     --to)
738 		msleep(10);
739 
740 	if (!to) {
741 		unsigned int state;
742 
743 		state = xenbus_read_unsigned(front_info->xb_dev->otherend,
744 					     "state", XenbusStateUnknown);
745 		DRM_ERROR("Backend state is %s while removing driver\n",
746 			  xenbus_strstate(state));
747 	}
748 
749 	xen_drm_drv_fini(front_info);
750 	xenbus_frontend_closed(dev);
751 	return 0;
752 }
753 
754 static const struct xenbus_device_id xen_driver_ids[] = {
755 	{ XENDISPL_DRIVER_NAME },
756 	{ "" }
757 };
758 
759 static struct xenbus_driver xen_driver = {
760 	.ids = xen_driver_ids,
761 	.probe = xen_drv_probe,
762 	.remove = xen_drv_remove,
763 	.otherend_changed = displback_changed,
764 	.not_essential = true,
765 };
766 
767 static int __init xen_drv_init(void)
768 {
769 	/* At the moment we only support case with XEN_PAGE_SIZE == PAGE_SIZE */
770 	if (XEN_PAGE_SIZE != PAGE_SIZE) {
771 		DRM_ERROR(XENDISPL_DRIVER_NAME ": different kernel and Xen page sizes are not supported: XEN_PAGE_SIZE (%lu) != PAGE_SIZE (%lu)\n",
772 			  XEN_PAGE_SIZE, PAGE_SIZE);
773 		return -ENODEV;
774 	}
775 
776 	if (!xen_domain())
777 		return -ENODEV;
778 
779 	if (!xen_has_pv_devices())
780 		return -ENODEV;
781 
782 	DRM_INFO("Registering XEN PV " XENDISPL_DRIVER_NAME "\n");
783 	return xenbus_register_frontend(&xen_driver);
784 }
785 
786 static void __exit xen_drv_fini(void)
787 {
788 	DRM_INFO("Unregistering XEN PV " XENDISPL_DRIVER_NAME "\n");
789 	xenbus_unregister_driver(&xen_driver);
790 }
791 
792 module_init(xen_drv_init);
793 module_exit(xen_drv_fini);
794 
795 MODULE_DESCRIPTION("Xen para-virtualized display device frontend");
796 MODULE_LICENSE("GPL");
797 MODULE_ALIAS("xen:" XENDISPL_DRIVER_NAME);
798