summaryrefslogtreecommitdiff
path: root/drivers/usb/misc/legousbtower.c
blob: 941c45028828d49f06e38513169009ee7b264084 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
// SPDX-License-Identifier: GPL-2.0+
/*
 * LEGO USB Tower driver
 *
 * Copyright (C) 2003 David Glance <davidgsf@sourceforge.net>
 *               2001-2004 Juergen Stuber <starblue@users.sourceforge.net>
 *
 * derived from USB Skeleton driver - 0.5
 * Copyright (C) 2001 Greg Kroah-Hartman (greg@kroah.com)
 *
 * History:
 *
 * 2001-10-13 - 0.1 js
 *   - first version
 * 2001-11-03 - 0.2 js
 *   - simplified buffering, one-shot URBs for writing
 * 2001-11-10 - 0.3 js
 *   - removed IOCTL (setting power/mode is more complicated, postponed)
 * 2001-11-28 - 0.4 js
 *   - added vendor commands for mode of operation and power level in open
 * 2001-12-04 - 0.5 js
 *   - set IR mode by default (by oversight 0.4 set VLL mode)
 * 2002-01-11 - 0.5? pcchan
 *   - make read buffer reusable and work around bytes_to_write issue between
 *     uhci and legusbtower
 * 2002-09-23 - 0.52 david (david@csse.uwa.edu.au)
 *   - imported into lejos project
 *   - changed wake_up to wake_up_interruptible
 *   - changed to use lego0 rather than tower0
 *   - changed dbg() to use __func__ rather than deprecated __func__
 * 2003-01-12 - 0.53 david (david@csse.uwa.edu.au)
 *   - changed read and write to write everything or
 *     timeout (from a patch by Chris Riesen and Brett Thaeler driver)
 *   - added ioctl functionality to set timeouts
 * 2003-07-18 - 0.54 davidgsf (david@csse.uwa.edu.au)
 *   - initial import into LegoUSB project
 *   - merge of existing LegoUSB.c driver
 * 2003-07-18 - 0.56 davidgsf (david@csse.uwa.edu.au)
 *   - port to 2.6 style driver
 * 2004-02-29 - 0.6 Juergen Stuber <starblue@users.sourceforge.net>
 *   - fix locking
 *   - unlink read URBs which are no longer needed
 *   - allow increased buffer size, eliminates need for timeout on write
 *   - have read URB running continuously
 *   - added poll
 *   - forbid seeking
 *   - added nonblocking I/O
 *   - changed back __func__ to __func__
 *   - read and log tower firmware version
 *   - reset tower on probe, avoids failure of first write
 * 2004-03-09 - 0.7 Juergen Stuber <starblue@users.sourceforge.net>
 *   - timeout read now only after inactivity, shorten default accordingly
 * 2004-03-11 - 0.8 Juergen Stuber <starblue@users.sourceforge.net>
 *   - log major, minor instead of possibly confusing device filename
 *   - whitespace cleanup
 * 2004-03-12 - 0.9 Juergen Stuber <starblue@users.sourceforge.net>
 *   - normalize whitespace in debug messages
 *   - take care about endianness in control message responses
 * 2004-03-13 - 0.91 Juergen Stuber <starblue@users.sourceforge.net>
 *   - make default intervals longer to accommodate current EHCI driver
 * 2004-03-19 - 0.92 Juergen Stuber <starblue@users.sourceforge.net>
 *   - replaced atomic_t by memory barriers
 * 2004-04-21 - 0.93 Juergen Stuber <starblue@users.sourceforge.net>
 *   - wait for completion of write urb in release (needed for remotecontrol)
 *   - corrected poll for write direction (missing negation)
 * 2004-04-22 - 0.94 Juergen Stuber <starblue@users.sourceforge.net>
 *   - make device locking interruptible
 * 2004-04-30 - 0.95 Juergen Stuber <starblue@users.sourceforge.net>
 *   - check for valid udev on resubmitting and unlinking urbs
 * 2004-08-03 - 0.96 Juergen Stuber <starblue@users.sourceforge.net>
 *   - move reset into open to clean out spurious data
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/kernel.h>
#include <linux/errno.h>
#include <linux/slab.h>
#include <linux/module.h>
#include <linux/completion.h>
#include <linux/mutex.h>
#include <linux/uaccess.h>
#include <linux/usb.h>
#include <linux/poll.h>


#define DRIVER_AUTHOR "Juergen Stuber <starblue@sourceforge.net>"
#define DRIVER_DESC "LEGO USB Tower Driver"


/* The defaults are chosen to work with the latest versions of leJOS and NQC.
 */

/* Some legacy software likes to receive packets in one piece.
 * In this case read_buffer_size should exceed the maximal packet length
 * (417 for datalog uploads), and packet_timeout should be set.
 */
static int read_buffer_size = 480;
module_param(read_buffer_size, int, 0);
MODULE_PARM_DESC(read_buffer_size, "Read buffer size");

/* Some legacy software likes to send packets in one piece.
 * In this case write_buffer_size should exceed the maximal packet length
 * (417 for firmware and program downloads).
 * A problem with long writes is that the following read may time out
 * if the software is not prepared to wait long enough.
 */
static int write_buffer_size = 480;
module_param(write_buffer_size, int, 0);
MODULE_PARM_DESC(write_buffer_size, "Write buffer size");

/* Some legacy software expects reads to contain whole LASM packets.
 * To achieve this, characters which arrive before a packet timeout
 * occurs will be returned in a single read operation.
 * A problem with long reads is that the software may time out
 * if it is not prepared to wait long enough.
 * The packet timeout should be greater than the time between the
 * reception of subsequent characters, which should arrive about
 * every 5ms for the standard 2400 baud.
 * Set it to 0 to disable.
 */
static int packet_timeout = 50;
module_param(packet_timeout, int, 0);
MODULE_PARM_DESC(packet_timeout, "Packet timeout in ms");

/* Some legacy software expects blocking reads to time out.
 * Timeout occurs after the specified time of read and write inactivity.
 * Set it to 0 to disable.
 */
static int read_timeout = 200;
module_param(read_timeout, int, 0);
MODULE_PARM_DESC(read_timeout, "Read timeout in ms");

/* As of kernel version 2.6.4 ehci-hcd uses an
 * "only one interrupt transfer per frame" shortcut
 * to simplify the scheduling of periodic transfers.
 * This conflicts with our standard 1ms intervals for in and out URBs.
 * We use default intervals of 2ms for in and 8ms for out transfers,
 * which is fast enough for 2400 baud and allows a small additional load.
 * Increase the interval to allow more devices that do interrupt transfers,
 * or set to 0 to use the standard interval from the endpoint descriptors.
 */
static int interrupt_in_interval = 2;
module_param(interrupt_in_interval, int, 0);
MODULE_PARM_DESC(interrupt_in_interval, "Interrupt in interval in ms");

static int interrupt_out_interval = 8;
module_param(interrupt_out_interval, int, 0);
MODULE_PARM_DESC(interrupt_out_interval, "Interrupt out interval in ms");

/* Define these values to match your device */
#define LEGO_USB_TOWER_VENDOR_ID	0x0694
#define LEGO_USB_TOWER_PRODUCT_ID	0x0001

/* Vendor requests */
#define LEGO_USB_TOWER_REQUEST_RESET		0x04
#define LEGO_USB_TOWER_REQUEST_GET_VERSION	0xFD

struct tower_reset_reply {
	__le16 size;		/* little-endian */
	__u8 err_code;
	__u8 spare;
} __attribute__ ((packed));

struct tower_get_version_reply {
	__le16 size;		/* little-endian */
	__u8 err_code;
	__u8 spare;
	__u8 major;
	__u8 minor;
	__le16 build_no;		/* little-endian */
} __attribute__ ((packed));


/* table of devices that work with this driver */
static const struct usb_device_id tower_table[] = {
	{ USB_DEVICE(LEGO_USB_TOWER_VENDOR_ID, LEGO_USB_TOWER_PRODUCT_ID) },
	{ }					/* Terminating entry */
};

MODULE_DEVICE_TABLE (usb, tower_table);
static DEFINE_MUTEX(open_disc_mutex);

#define LEGO_USB_TOWER_MINOR_BASE	160


/* Structure to hold all of our device specific stuff */
struct lego_usb_tower {
	struct mutex		lock;		/* locks this structure */
	struct usb_device*	udev;		/* save off the usb device pointer */
	unsigned char		minor;		/* the starting minor number for this device */

	int			open_count;	/* number of times this port has been opened */

	char*			read_buffer;
	size_t			read_buffer_length; /* this much came in */
	size_t			read_packet_length; /* this much will be returned on read */
	spinlock_t		read_buffer_lock;
	int			packet_timeout_jiffies;
	unsigned long		read_last_arrival;

	wait_queue_head_t	read_wait;
	wait_queue_head_t	write_wait;

	char*			interrupt_in_buffer;
	struct usb_endpoint_descriptor* interrupt_in_endpoint;
	struct urb*		interrupt_in_urb;
	int			interrupt_in_interval;
	int			interrupt_in_running;
	int			interrupt_in_done;

	char*			interrupt_out_buffer;
	struct usb_endpoint_descriptor* interrupt_out_endpoint;
	struct urb*		interrupt_out_urb;
	int			interrupt_out_interval;
	int			interrupt_out_busy;

};


/* local function prototypes */
static ssize_t tower_read	(struct file *file, char __user *buffer, size_t count, loff_t *ppos);
static ssize_t tower_write	(struct file *file, const char __user *buffer, size_t count, loff_t *ppos);
static inline void tower_delete (struct lego_usb_tower *dev);
static int tower_open		(struct inode *inode, struct file *file);
static int tower_release	(struct inode *inode, struct file *file);
static __poll_t tower_poll	(struct file *file, poll_table *wait);
static loff_t tower_llseek	(struct file *file, loff_t off, int whence);

static void tower_abort_transfers (struct lego_usb_tower *dev);
static void tower_check_for_read_packet (struct lego_usb_tower *dev);
static void tower_interrupt_in_callback (struct urb *urb);
static void tower_interrupt_out_callback (struct urb *urb);

static int  tower_probe	(struct usb_interface *interface, const struct usb_device_id *id);
static void tower_disconnect	(struct usb_interface *interface);


/* file operations needed when we register this driver */
static const struct file_operations tower_fops = {
	.owner =	THIS_MODULE,
	.read  =	tower_read,
	.write =	tower_write,
	.open =		tower_open,
	.release =	tower_release,
	.poll =		tower_poll,
	.llseek =	tower_llseek,
};

static char *legousbtower_devnode(struct device *dev, umode_t *mode)
{
	return kasprintf(GFP_KERNEL, "usb/%s", dev_name(dev));
}

/*
 * usb class driver info in order to get a minor number from the usb core,
 * and to have the device registered with the driver core
 */
static struct usb_class_driver tower_class = {
	.name =		"legousbtower%d",
	.devnode = 	legousbtower_devnode,
	.fops =		&tower_fops,
	.minor_base =	LEGO_USB_TOWER_MINOR_BASE,
};


/* usb specific object needed to register this driver with the usb subsystem */
static struct usb_driver tower_driver = {
	.name =		"legousbtower",
	.probe =	tower_probe,
	.disconnect =	tower_disconnect,
	.id_table =	tower_table,
};


/**
 *	lego_usb_tower_debug_data
 */
static inline void lego_usb_tower_debug_data(struct device *dev,
					     const char *function, int size,
					     const unsigned char *data)
{
	dev_dbg(dev, "%s - length = %d, data = %*ph\n",
		function, size, size, data);
}


/**
 *	tower_delete
 */
static inline void tower_delete (struct lego_usb_tower *dev)
{
	tower_abort_transfers (dev);

	/* free data structures */
	usb_free_urb(dev->interrupt_in_urb);
	usb_free_urb(dev->interrupt_out_urb);
	kfree (dev->read_buffer);
	kfree (dev->interrupt_in_buffer);
	kfree (dev->interrupt_out_buffer);
	kfree (dev);
}


/**
 *	tower_open
 */
static int tower_open (struct inode *inode, struct file *file)
{
	struct lego_usb_tower *dev = NULL;
	int subminor;
	int retval = 0;
	struct usb_interface *interface;
	struct tower_reset_reply *reset_reply;
	int result;

	reset_reply = kmalloc(sizeof(*reset_reply), GFP_KERNEL);

	if (!reset_reply) {
		retval = -ENOMEM;
		goto exit;
	}

	nonseekable_open(inode, file);
	subminor = iminor(inode);

	interface = usb_find_interface (&tower_driver, subminor);

	if (!interface) {
		pr_err("error, can't find device for minor %d\n", subminor);
		retval = -ENODEV;
		goto exit;
	}

	mutex_lock(&open_disc_mutex);
	dev = usb_get_intfdata(interface);

	if (!dev) {
		mutex_unlock(&open_disc_mutex);
		retval = -ENODEV;
		goto exit;
	}

	/* lock this device */
	if (mutex_lock_interruptible(&dev->lock)) {
		mutex_unlock(&open_disc_mutex);
	        retval = -ERESTARTSYS;
		goto exit;
	}


	/* allow opening only once */
	if (dev->open_count) {
		mutex_unlock(&open_disc_mutex);
		retval = -EBUSY;
		goto unlock_exit;
	}
	dev->open_count = 1;
	mutex_unlock(&open_disc_mutex);

	/* reset the tower */
	result = usb_control_msg (dev->udev,
				  usb_rcvctrlpipe(dev->udev, 0),
				  LEGO_USB_TOWER_REQUEST_RESET,
				  USB_TYPE_VENDOR | USB_DIR_IN | USB_RECIP_DEVICE,
				  0,
				  0,
				  reset_reply,
				  sizeof(*reset_reply),
				  1000);
	if (result < 0) {
		dev_err(&dev->udev->dev,
			"LEGO USB Tower reset control request failed\n");
		retval = result;
		goto unlock_exit;
	}

	/* initialize in direction */
	dev->read_buffer_length = 0;
	dev->read_packet_length = 0;
	usb_fill_int_urb (dev->interrupt_in_urb,
			  dev->udev,
			  usb_rcvintpipe(dev->udev, dev->interrupt_in_endpoint->bEndpointAddress),
			  dev->interrupt_in_buffer,
			  usb_endpoint_maxp(dev->interrupt_in_endpoint),
			  tower_interrupt_in_callback,
			  dev,
			  dev->interrupt_in_interval);

	dev->interrupt_in_running = 1;
	dev->interrupt_in_done = 0;
	mb();

	retval = usb_submit_urb (dev->interrupt_in_urb, GFP_KERNEL);
	if (retval) {
		dev_err(&dev->udev->dev,
			"Couldn't submit interrupt_in_urb %d\n", retval);
		dev->interrupt_in_running = 0;
		dev->open_count = 0;
		goto unlock_exit;
	}

	/* save device in the file's private structure */
	file->private_data = dev;

unlock_exit:
	mutex_unlock(&dev->lock);

exit:
	kfree(reset_reply);
	return retval;
}

/**
 *	tower_release
 */
static int tower_release (struct inode *inode, struct file *file)
{
	struct lego_usb_tower *dev;
	int retval = 0;

	dev = file->private_data;

	if (dev == NULL) {
		retval = -ENODEV;
		goto exit_nolock;
	}

	mutex_lock(&open_disc_mutex);
	if (mutex_lock_interruptible(&dev->lock)) {
	        retval = -ERESTARTSYS;
		goto exit;
	}

	if (dev->open_count != 1) {
		dev_dbg(&dev->udev->dev, "%s: device not opened exactly once\n",
			__func__);
		retval = -ENODEV;
		goto unlock_exit;
	}
	if (dev->udev == NULL) {
		/* the device was unplugged before the file was released */

		/* unlock here as tower_delete frees dev */
		mutex_unlock(&dev->lock);
		tower_delete (dev);
		goto exit;
	}

	/* wait until write transfer is finished */
	if (dev->interrupt_out_busy) {
		wait_event_interruptible_timeout (dev->write_wait, !dev->interrupt_out_busy, 2 * HZ);
	}
	tower_abort_transfers (dev);
	dev->open_count = 0;

unlock_exit:
	mutex_unlock(&dev->lock);

exit:
	mutex_unlock(&open_disc_mutex);
exit_nolock:
	return retval;
}


/**
 *	tower_abort_transfers
 *      aborts transfers and frees associated data structures
 */
static void tower_abort_transfers (struct lego_usb_tower *dev)
{
	if (dev == NULL)
		return;

	/* shutdown transfer */
	if (dev->interrupt_in_running) {
		dev->interrupt_in_running = 0;
		mb();
		if (dev->udev)
			usb_kill_urb (dev->interrupt_in_urb);
	}
	if (dev->interrupt_out_busy && dev->udev)
		usb_kill_urb(dev->interrupt_out_urb);
}


/**
 *	tower_check_for_read_packet
 *
 *      To get correct semantics for signals and non-blocking I/O
 *      with packetizing we pretend not to see any data in the read buffer
 *      until it has been there unchanged for at least
 *      dev->packet_timeout_jiffies, or until the buffer is full.
 */
static void tower_check_for_read_packet (struct lego_usb_tower *dev)
{
	spin_lock_irq (&dev->read_buffer_lock);
	if (!packet_timeout
	    || time_after(jiffies, dev->read_last_arrival + dev->packet_timeout_jiffies)
	    || dev->read_buffer_length == read_buffer_size) {
		dev->read_packet_length = dev->read_buffer_length;
	}
	dev->interrupt_in_done = 0;
	spin_unlock_irq (&dev->read_buffer_lock);
}


/**
 *	tower_poll
 */
static __poll_t tower_poll (struct file *file, poll_table *wait)
{
	struct lego_usb_tower *dev;
	__poll_t mask = 0;

	dev = file->private_data;

	if (!dev->udev)
		return POLLERR | POLLHUP;

	poll_wait(file, &dev->read_wait, wait);
	poll_wait(file, &dev->write_wait, wait);

	tower_check_for_read_packet(dev);
	if (dev->read_packet_length > 0) {
		mask |= POLLIN | POLLRDNORM;
	}
	if (!dev->interrupt_out_busy) {
		mask |= POLLOUT | POLLWRNORM;
	}

	return mask;
}


/**
 *	tower_llseek
 */
static loff_t tower_llseek (struct file *file, loff_t off, int whence)
{
	return -ESPIPE;		/* unseekable */
}


/**
 *	tower_read
 */
static ssize_t tower_read (struct file *file, char __user *buffer, size_t count, loff_t *ppos)
{
	struct lego_usb_tower *dev;
	size_t bytes_to_read;
	int i;
	int retval = 0;
	unsigned long timeout = 0;

	dev = file->private_data;

	/* lock this object */
	if (mutex_lock_interruptible(&dev->lock)) {
		retval = -ERESTARTSYS;
		goto exit;
	}

	/* verify that the device wasn't unplugged */
	if (dev->udev == NULL) {
		retval = -ENODEV;
		pr_err("No device or device unplugged %d\n", retval);
		goto unlock_exit;
	}

	/* verify that we actually have some data to read */
	if (count == 0) {
		dev_dbg(&dev->udev->dev, "read request of 0 bytes\n");
		goto unlock_exit;
	}

	if (read_timeout) {
		timeout = jiffies + msecs_to_jiffies(read_timeout);
	}

	/* wait for data */
	tower_check_for_read_packet (dev);
	while (dev->read_packet_length == 0) {
		if (file->f_flags & O_NONBLOCK) {
			retval = -EAGAIN;
			goto unlock_exit;
		}
		retval = wait_event_interruptible_timeout(dev->read_wait, dev->interrupt_in_done, dev->packet_timeout_jiffies);
		if (retval < 0) {
			goto unlock_exit;
		}

		/* reset read timeout during read or write activity */
		if (read_timeout
		    && (dev->read_buffer_length || dev->interrupt_out_busy)) {
			timeout = jiffies + msecs_to_jiffies(read_timeout);
		}
		/* check for read timeout */
		if (read_timeout && time_after (jiffies, timeout)) {
			retval = -ETIMEDOUT;
			goto unlock_exit;
		}
		tower_check_for_read_packet (dev);
	}

	/* copy the data from read_buffer into userspace */
	bytes_to_read = min(count, dev->read_packet_length);

	if (copy_to_user (buffer, dev->read_buffer, bytes_to_read)) {
		retval = -EFAULT;
		goto unlock_exit;
	}

	spin_lock_irq (&dev->read_buffer_lock);
	dev->read_buffer_length -= bytes_to_read;
	dev->read_packet_length -= bytes_to_read;
	for (i=0; i<dev->read_buffer_length; i++) {
		dev->read_buffer[i] = dev->read_buffer[i+bytes_to_read];
	}
	spin_unlock_irq (&dev->read_buffer_lock);

	retval = bytes_to_read;

unlock_exit:
	/* unlock the device */
	mutex_unlock(&dev->lock);

exit:
	return retval;
}


/**
 *	tower_write
 */
static ssize_t tower_write (struct file *file, const char __user *buffer, size_t count, loff_t *ppos)
{
	struct lego_usb_tower *dev;
	size_t bytes_to_write;
	int retval = 0;

	dev = file->private_data;

	/* lock this object */
	if (mutex_lock_interruptible(&dev->lock)) {
		retval = -ERESTARTSYS;
		goto exit;
	}

	/* verify that the device wasn't unplugged */
	if (dev->udev == NULL) {
		retval = -ENODEV;
		pr_err("No device or device unplugged %d\n", retval);
		goto unlock_exit;
	}

	/* verify that we actually have some data to write */
	if (count == 0) {
		dev_dbg(&dev->udev->dev, "write request of 0 bytes\n");
		goto unlock_exit;
	}

	/* wait until previous transfer is finished */
	while (dev->interrupt_out_busy) {
		if (file->f_flags & O_NONBLOCK) {
			retval = -EAGAIN;
			goto unlock_exit;
		}
		retval = wait_event_interruptible (dev->write_wait, !dev->interrupt_out_busy);
		if (retval) {
			goto unlock_exit;
		}
	}

	/* write the data into interrupt_out_buffer from userspace */
	bytes_to_write = min_t(int, count, write_buffer_size);
	dev_dbg(&dev->udev->dev, "%s: count = %zd, bytes_to_write = %zd\n",
		__func__, count, bytes_to_write);

	if (copy_from_user (dev->interrupt_out_buffer, buffer, bytes_to_write)) {
		retval = -EFAULT;
		goto unlock_exit;
	}

	/* send off the urb */
	usb_fill_int_urb(dev->interrupt_out_urb,
			 dev->udev,
			 usb_sndintpipe(dev->udev, dev->interrupt_out_endpoint->bEndpointAddress),
			 dev->interrupt_out_buffer,
			 bytes_to_write,
			 tower_interrupt_out_callback,
			 dev,
			 dev->interrupt_out_interval);

	dev->interrupt_out_busy = 1;
	wmb();

	retval = usb_submit_urb (dev->interrupt_out_urb, GFP_KERNEL);
	if (retval) {
		dev->interrupt_out_busy = 0;
		dev_err(&dev->udev->dev,
			"Couldn't submit interrupt_out_urb %d\n", retval);
		goto unlock_exit;
	}
	retval = bytes_to_write;

unlock_exit:
	/* unlock the device */
	mutex_unlock(&dev->lock);

exit:
	return retval;
}


/**
 *	tower_interrupt_in_callback
 */
static void tower_interrupt_in_callback (struct urb *urb)
{
	struct lego_usb_tower *dev = urb->context;
	int status = urb->status;
	int retval;

	lego_usb_tower_debug_data(&dev->udev->dev, __func__,
				  urb->actual_length, urb->transfer_buffer);

	if (status) {
		if (status == -ENOENT ||
		    status == -ECONNRESET ||
		    status == -ESHUTDOWN) {
			goto exit;
		} else {
			dev_dbg(&dev->udev->dev,
				"%s: nonzero status received: %d\n", __func__,
				status);
			goto resubmit; /* maybe we can recover */
		}
	}

	if (urb->actual_length > 0) {
		spin_lock (&dev->read_buffer_lock);
		if (dev->read_buffer_length + urb->actual_length < read_buffer_size) {
			memcpy (dev->read_buffer + dev->read_buffer_length,
				dev->interrupt_in_buffer,
				urb->actual_length);
			dev->read_buffer_length += urb->actual_length;
			dev->read_last_arrival = jiffies;
			dev_dbg(&dev->udev->dev, "%s: received %d bytes\n",
				__func__, urb->actual_length);
		} else {
			pr_warn("read_buffer overflow, %d bytes dropped\n",
				urb->actual_length);
		}
		spin_unlock (&dev->read_buffer_lock);
	}

resubmit:
	/* resubmit if we're still running */
	if (dev->interrupt_in_running && dev->udev) {
		retval = usb_submit_urb (dev->interrupt_in_urb, GFP_ATOMIC);
		if (retval)
			dev_err(&dev->udev->dev,
				"%s: usb_submit_urb failed (%d)\n",
				__func__, retval);
	}

exit:
	dev->interrupt_in_done = 1;
	wake_up_interruptible (&dev->read_wait);
}


/**
 *	tower_interrupt_out_callback
 */
static void tower_interrupt_out_callback (struct urb *urb)
{
	struct lego_usb_tower *dev = urb->context;
	int status = urb->status;

	lego_usb_tower_debug_data(&dev->udev->dev, __func__,
				  urb->actual_length, urb->transfer_buffer);

	/* sync/async unlink faults aren't errors */
	if (status && !(status == -ENOENT ||
			status == -ECONNRESET ||
			status == -ESHUTDOWN)) {
		dev_dbg(&dev->udev->dev,
			"%s: nonzero write bulk status received: %d\n", __func__,
			status);
	}

	dev->interrupt_out_busy = 0;
	wake_up_interruptible(&dev->write_wait);
}


/**
 *	tower_probe
 *
 *	Called by the usb core when a new device is connected that it thinks
 *	this driver might be interested in.
 */
static int tower_probe (struct usb_interface *interface, const struct usb_device_id *id)
{
	struct device *idev = &interface->dev;
	struct usb_device *udev = interface_to_usbdev(interface);
	struct lego_usb_tower *dev = NULL;
	struct tower_get_version_reply *get_version_reply = NULL;
	int retval = -ENOMEM;
	int result;

	/* allocate memory for our device state and initialize it */

	dev = kmalloc (sizeof(struct lego_usb_tower), GFP_KERNEL);

	if (!dev)
		goto exit;

	mutex_init(&dev->lock);

	dev->udev = udev;
	dev->open_count = 0;

	dev->read_buffer = NULL;
	dev->read_buffer_length = 0;
	dev->read_packet_length = 0;
	spin_lock_init (&dev->read_buffer_lock);
	dev->packet_timeout_jiffies = msecs_to_jiffies(packet_timeout);
	dev->read_last_arrival = jiffies;

	init_waitqueue_head (&dev->read_wait);
	init_waitqueue_head (&dev->write_wait);

	dev->interrupt_in_buffer = NULL;
	dev->interrupt_in_endpoint = NULL;
	dev->interrupt_in_urb = NULL;
	dev->interrupt_in_running = 0;
	dev->interrupt_in_done = 0;

	dev->interrupt_out_buffer = NULL;
	dev->interrupt_out_endpoint = NULL;
	dev->interrupt_out_urb = NULL;
	dev->interrupt_out_busy = 0;

	result = usb_find_common_endpoints_reverse(interface->cur_altsetting,
			NULL, NULL,
			&dev->interrupt_in_endpoint,
			&dev->interrupt_out_endpoint);
	if (result) {
		dev_err(idev, "interrupt endpoints not found\n");
		retval = result;
		goto error;
	}

	dev->read_buffer = kmalloc (read_buffer_size, GFP_KERNEL);
	if (!dev->read_buffer)
		goto error;
	dev->interrupt_in_buffer = kmalloc (usb_endpoint_maxp(dev->interrupt_in_endpoint), GFP_KERNEL);
	if (!dev->interrupt_in_buffer)
		goto error;
	dev->interrupt_in_urb = usb_alloc_urb(0, GFP_KERNEL);
	if (!dev->interrupt_in_urb)
		goto error;
	dev->interrupt_out_buffer = kmalloc (write_buffer_size, GFP_KERNEL);
	if (!dev->interrupt_out_buffer)
		goto error;
	dev->interrupt_out_urb = usb_alloc_urb(0, GFP_KERNEL);
	if (!dev->interrupt_out_urb)
		goto error;
	dev->interrupt_in_interval = interrupt_in_interval ? interrupt_in_interval : dev->interrupt_in_endpoint->bInterval;
	dev->interrupt_out_interval = interrupt_out_interval ? interrupt_out_interval : dev->interrupt_out_endpoint->bInterval;

	get_version_reply = kmalloc(sizeof(*get_version_reply), GFP_KERNEL);

	if (!get_version_reply) {
		retval = -ENOMEM;
		goto error;
	}

	/* get the firmware version and log it */
	result = usb_control_msg (udev,
				  usb_rcvctrlpipe(udev, 0),
				  LEGO_USB_TOWER_REQUEST_GET_VERSION,
				  USB_TYPE_VENDOR | USB_DIR_IN | USB_RECIP_DEVICE,
				  0,
				  0,
				  get_version_reply,
				  sizeof(*get_version_reply),
				  1000);
	if (result < 0) {
		dev_err(idev, "LEGO USB Tower get version control request failed\n");
		retval = result;
		goto error;
	}
	dev_info(&interface->dev,
		 "LEGO USB Tower firmware version is %d.%d build %d\n",
		 get_version_reply->major,
		 get_version_reply->minor,
		 le16_to_cpu(get_version_reply->build_no));

	/* we can register the device now, as it is ready */
	usb_set_intfdata (interface, dev);

	retval = usb_register_dev (interface, &tower_class);

	if (retval) {
		/* something prevented us from registering this driver */
		dev_err(idev, "Not able to get a minor for this device.\n");
		usb_set_intfdata (interface, NULL);
		goto error;
	}
	dev->minor = interface->minor;

	/* let the user know what node this device is now attached to */
	dev_info(&interface->dev, "LEGO USB Tower #%d now attached to major "
		 "%d minor %d\n", (dev->minor - LEGO_USB_TOWER_MINOR_BASE),
		 USB_MAJOR, dev->minor);

exit:
	kfree(get_version_reply);
	return retval;

error:
	kfree(get_version_reply);
	tower_delete(dev);
	return retval;
}


/**
 *	tower_disconnect
 *
 *	Called by the usb core when the device is removed from the system.
 */
static void tower_disconnect (struct usb_interface *interface)
{
	struct lego_usb_tower *dev;
	int minor;

	dev = usb_get_intfdata (interface);
	mutex_lock(&open_disc_mutex);
	usb_set_intfdata (interface, NULL);

	minor = dev->minor;

	/* give back our minor */
	usb_deregister_dev (interface, &tower_class);

	mutex_lock(&dev->lock);
	mutex_unlock(&open_disc_mutex);

	/* if the device is not opened, then we clean up right now */
	if (!dev->open_count) {
		mutex_unlock(&dev->lock);
		tower_delete (dev);
	} else {
		dev->udev = NULL;
		/* wake up pollers */
		wake_up_interruptible_all(&dev->read_wait);
		wake_up_interruptible_all(&dev->write_wait);
		mutex_unlock(&dev->lock);
	}

	dev_info(&interface->dev, "LEGO USB Tower #%d now disconnected\n",
		 (minor - LEGO_USB_TOWER_MINOR_BASE));
}

module_usb_driver(tower_driver);

MODULE_AUTHOR(DRIVER_AUTHOR);
MODULE_DESCRIPTION(DRIVER_DESC);
#ifdef MODULE_LICENSE
MODULE_LICENSE("GPL");
#endif