summaryrefslogtreecommitdiffstats
path: root/drivers/fsi/fsi-master-gpio.c
blob: 40cbaf96547ca198ecf5b7504431805415d0c660 (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
/*
 * A FSI master controller, using a simple GPIO bit-banging interface
 */

#include <linux/crc4.h>
#include <linux/delay.h>
#include <linux/device.h>
#include <linux/fsi.h>
#include <linux/gpio/consumer.h>
#include <linux/io.h>
#include <linux/irqflags.h>
#include <linux/module.h>
#include <linux/of.h>
#include <linux/platform_device.h>
#include <linux/slab.h>

#include "fsi-master.h"

#define	FSI_GPIO_STD_DLY	1	/* Standard pin delay in nS */
#define	FSI_ECHO_DELAY_CLOCKS	16	/* Number clocks for echo delay */
#define	FSI_SEND_DELAY_CLOCKS	16	/* Number clocks for send delay */
#define	FSI_PRE_BREAK_CLOCKS	50	/* Number clocks to prep for break */
#define	FSI_BREAK_CLOCKS	256	/* Number of clocks to issue break */
#define	FSI_POST_BREAK_CLOCKS	16000	/* Number clocks to set up cfam */
#define	FSI_INIT_CLOCKS		5000	/* Clock out any old data */
#define	FSI_GPIO_DPOLL_CLOCKS	50      /* < 21 will cause slave to hang */
#define	FSI_GPIO_EPOLL_CLOCKS	50      /* Number of clocks for E_POLL retry */
#define	FSI_GPIO_STD_DELAY	10	/* Standard GPIO delay in nS */
					/* todo: adjust down as low as */
					/* possible or eliminate */
#define FSI_CRC_ERR_RETRIES	10

#define	FSI_GPIO_CMD_DPOLL      0x2
#define	FSI_GPIO_CMD_EPOLL      0x3
#define	FSI_GPIO_CMD_TERM	0x3f
#define FSI_GPIO_CMD_ABS_AR	0x4
#define FSI_GPIO_CMD_REL_AR	0x5
#define FSI_GPIO_CMD_SAME_AR	0x3	/* but only a 2-bit opcode... */

/* Slave responses */
#define	FSI_GPIO_RESP_ACK	0	/* Success */
#define	FSI_GPIO_RESP_BUSY	1	/* Slave busy */
#define	FSI_GPIO_RESP_ERRA	2	/* Any (misc) Error */
#define	FSI_GPIO_RESP_ERRC	3	/* Slave reports master CRC error */

#define	FSI_GPIO_MAX_BUSY	200
#define	FSI_GPIO_MTOE_COUNT	1000
#define	FSI_GPIO_DRAIN_BITS	20
#define	FSI_GPIO_CRC_SIZE	4
#define	FSI_GPIO_MSG_ID_SIZE		2
#define	FSI_GPIO_MSG_RESPID_SIZE	2

#define LAST_ADDR_INVALID		0x1

struct fsi_master_gpio {
	struct fsi_master	master;
	struct device		*dev;
	struct mutex		cmd_lock;	/* mutex for command ordering */
	struct gpio_desc	*gpio_clk;
	struct gpio_desc	*gpio_data;
	struct gpio_desc	*gpio_trans;	/* Voltage translator */
	struct gpio_desc	*gpio_enable;	/* FSI enable */
	struct gpio_desc	*gpio_mux;	/* Mux control */
	bool			external_mode;
	bool			no_delays;
	uint32_t		last_addr;
	uint8_t			t_send_delay;
	uint8_t			t_echo_delay;
};

#define CREATE_TRACE_POINTS
#include <trace/events/fsi_master_gpio.h>

#define to_fsi_master_gpio(m) container_of(m, struct fsi_master_gpio, master)

struct fsi_gpio_msg {
	uint64_t	msg;
	uint8_t		bits;
};

static void clock_toggle(struct fsi_master_gpio *master, int count)
{
	int i;

	for (i = 0; i < count; i++) {
		if (!master->no_delays)
			ndelay(FSI_GPIO_STD_DLY);
		gpiod_set_value(master->gpio_clk, 0);
		if (!master->no_delays)
			ndelay(FSI_GPIO_STD_DLY);
		gpiod_set_value(master->gpio_clk, 1);
	}
}

static int sda_clock_in(struct fsi_master_gpio *master)
{
	int in;

	if (!master->no_delays)
		ndelay(FSI_GPIO_STD_DLY);
	gpiod_set_value(master->gpio_clk, 0);

	/* Dummy read to feed the synchronizers */
	gpiod_get_value(master->gpio_data);

	/* Actual data read */
	in = gpiod_get_value(master->gpio_data);
	if (!master->no_delays)
		ndelay(FSI_GPIO_STD_DLY);
	gpiod_set_value(master->gpio_clk, 1);
	return in ? 1 : 0;
}

static void sda_out(struct fsi_master_gpio *master, int value)
{
	gpiod_set_value(master->gpio_data, value);
}

static void set_sda_input(struct fsi_master_gpio *master)
{
	gpiod_direction_input(master->gpio_data);
	gpiod_set_value(master->gpio_trans, 0);
}

static void set_sda_output(struct fsi_master_gpio *master, int value)
{
	gpiod_set_value(master->gpio_trans, 1);
	gpiod_direction_output(master->gpio_data, value);
}

static void clock_zeros(struct fsi_master_gpio *master, int count)
{
	trace_fsi_master_gpio_clock_zeros(master, count);
	set_sda_output(master, 1);
	clock_toggle(master, count);
}

static void echo_delay(struct fsi_master_gpio *master)
{
	clock_zeros(master, master->t_echo_delay);
}


static void serial_in(struct fsi_master_gpio *master, struct fsi_gpio_msg *msg,
			uint8_t num_bits)
{
	uint8_t bit, in_bit;

	set_sda_input(master);

	for (bit = 0; bit < num_bits; bit++) {
		in_bit = sda_clock_in(master);
		msg->msg <<= 1;
		msg->msg |= ~in_bit & 0x1;	/* Data is active low */
	}
	msg->bits += num_bits;

	trace_fsi_master_gpio_in(master, num_bits, msg->msg);
}

static void serial_out(struct fsi_master_gpio *master,
			const struct fsi_gpio_msg *cmd)
{
	uint8_t bit;
	uint64_t msg = ~cmd->msg;	/* Data is active low */
	uint64_t sda_mask = 0x1ULL << (cmd->bits - 1);
	uint64_t last_bit = ~0;
	int next_bit;

	trace_fsi_master_gpio_out(master, cmd->bits, cmd->msg);

	if (!cmd->bits) {
		dev_warn(master->dev, "trying to output 0 bits\n");
		return;
	}
	set_sda_output(master, 0);

	/* Send the start bit */
	sda_out(master, 0);
	clock_toggle(master, 1);

	/* Send the message */
	for (bit = 0; bit < cmd->bits; bit++) {
		next_bit = (msg & sda_mask) >> (cmd->bits - 1);
		if (last_bit ^ next_bit) {
			sda_out(master, next_bit);
			last_bit = next_bit;
		}
		clock_toggle(master, 1);
		msg <<= 1;
	}
}

static void msg_push_bits(struct fsi_gpio_msg *msg, uint64_t data, int bits)
{
	msg->msg <<= bits;
	msg->msg |= data & ((1ull << bits) - 1);
	msg->bits += bits;
}

static void msg_push_crc(struct fsi_gpio_msg *msg)
{
	uint8_t crc;
	int top;

	top = msg->bits & 0x3;

	/* start bit, and any non-aligned top bits */
	crc = crc4(0, 1 << top | msg->msg >> (msg->bits - top), top + 1);

	/* aligned bits */
	crc = crc4(crc, msg->msg, msg->bits - top);

	msg_push_bits(msg, crc, 4);
}

static bool check_same_address(struct fsi_master_gpio *master, int id,
		uint32_t addr)
{
	/* this will also handle LAST_ADDR_INVALID */
	return master->last_addr == (((id & 0x3) << 21) | (addr & ~0x3));
}

static bool check_relative_address(struct fsi_master_gpio *master, int id,
		uint32_t addr, uint32_t *rel_addrp)
{
	uint32_t last_addr = master->last_addr;
	int32_t rel_addr;

	if (last_addr == LAST_ADDR_INVALID)
		return false;

	/* We may be in 23-bit addressing mode, which uses the id as the
	 * top two address bits. So, if we're referencing a different ID,
	 * use absolute addresses.
	 */
	if (((last_addr >> 21) & 0x3) != id)
		return false;

	/* remove the top two bits from any 23-bit addressing */
	last_addr &= (1 << 21) - 1;

	/* We know that the addresses are limited to 21 bits, so this won't
	 * overflow the signed rel_addr */
	rel_addr = addr - last_addr;
	if (rel_addr > 255 || rel_addr < -256)
		return false;

	*rel_addrp = (uint32_t)rel_addr;

	return true;
}

static void last_address_update(struct fsi_master_gpio *master,
		int id, bool valid, uint32_t addr)
{
	if (!valid)
		master->last_addr = LAST_ADDR_INVALID;
	else
		master->last_addr = ((id & 0x3) << 21) | (addr & ~0x3);
}

/*
 * Encode an Absolute/Relative/Same Address command
 */
static void build_ar_command(struct fsi_master_gpio *master,
		struct fsi_gpio_msg *cmd, uint8_t id,
		uint32_t addr, size_t size, const void *data)
{
	int i, addr_bits, opcode_bits;
	bool write = !!data;
	uint8_t ds, opcode;
	uint32_t rel_addr;

	cmd->bits = 0;
	cmd->msg = 0;

	/* we have 21 bits of address max */
	addr &= ((1 << 21) - 1);

	/* cmd opcodes are variable length - SAME_AR is only two bits */
	opcode_bits = 3;

	if (check_same_address(master, id, addr)) {
		/* we still address the byte offset within the word */
		addr_bits = 2;
		opcode_bits = 2;
		opcode = FSI_GPIO_CMD_SAME_AR;
		trace_fsi_master_gpio_cmd_same_addr(master);

	} else if (check_relative_address(master, id, addr, &rel_addr)) {
		/* 8 bits plus sign */
		addr_bits = 9;
		addr = rel_addr;
		opcode = FSI_GPIO_CMD_REL_AR;
		trace_fsi_master_gpio_cmd_rel_addr(master, rel_addr);

	} else {
		addr_bits = 21;
		opcode = FSI_GPIO_CMD_ABS_AR;
		trace_fsi_master_gpio_cmd_abs_addr(master, addr);
	}

	/*
	 * The read/write size is encoded in the lower bits of the address
	 * (as it must be naturally-aligned), and the following ds bit.
	 *
	 *	size	addr:1	addr:0	ds
	 *	1	x	x	0
	 *	2	x	0	1
	 *	4	0	1	1
	 *
	 */
	ds = size > 1 ? 1 : 0;
	addr &= ~(size - 1);
	if (size == 4)
		addr |= 1;

	msg_push_bits(cmd, id, 2);
	msg_push_bits(cmd, opcode, opcode_bits);
	msg_push_bits(cmd, write ? 0 : 1, 1);
	msg_push_bits(cmd, addr, addr_bits);
	msg_push_bits(cmd, ds, 1);
	for (i = 0; write && i < size; i++)
		msg_push_bits(cmd, ((uint8_t *)data)[i], 8);

	msg_push_crc(cmd);
}

static void build_dpoll_command(struct fsi_gpio_msg *cmd, uint8_t slave_id)
{
	cmd->bits = 0;
	cmd->msg = 0;

	msg_push_bits(cmd, slave_id, 2);
	msg_push_bits(cmd, FSI_GPIO_CMD_DPOLL, 3);
	msg_push_crc(cmd);
}

static void build_epoll_command(struct fsi_gpio_msg *cmd, uint8_t slave_id)
{
	cmd->bits = 0;
	cmd->msg = 0;

	msg_push_bits(cmd, slave_id, 2);
	msg_push_bits(cmd, FSI_GPIO_CMD_EPOLL, 3);
	msg_push_crc(cmd);
}

static void build_term_command(struct fsi_gpio_msg *cmd, uint8_t slave_id)
{
	cmd->bits = 0;
	cmd->msg = 0;

	msg_push_bits(cmd, slave_id, 2);
	msg_push_bits(cmd, FSI_GPIO_CMD_TERM, 6);
	msg_push_crc(cmd);
}

/*
 * Note: callers rely specifically on this returning -EAGAIN for
 * a CRC error detected in the response. Use other error code
 * for other situations. It will be converted to something else
 * higher up the stack before it reaches userspace.
 */
static int read_one_response(struct fsi_master_gpio *master,
		uint8_t data_size, struct fsi_gpio_msg *msgp, uint8_t *tagp)
{
	struct fsi_gpio_msg msg;
	unsigned long flags;
	uint32_t crc;
	uint8_t tag;
	int i;

	local_irq_save(flags);

	/* wait for the start bit */
	for (i = 0; i < FSI_GPIO_MTOE_COUNT; i++) {
		msg.bits = 0;
		msg.msg = 0;
		serial_in(master, &msg, 1);
		if (msg.msg)
			break;
	}
	if (i == FSI_GPIO_MTOE_COUNT) {
		dev_dbg(master->dev,
			"Master time out waiting for response\n");
		local_irq_restore(flags);
		return -ETIMEDOUT;
	}

	msg.bits = 0;
	msg.msg = 0;

	/* Read slave ID & response tag */
	serial_in(master, &msg, 4);

	tag = msg.msg & 0x3;

	/* If we have an ACK and we're expecting data, clock the data in too */
	if (tag == FSI_GPIO_RESP_ACK && data_size)
		serial_in(master, &msg, data_size * 8);

	/* read CRC */
	serial_in(master, &msg, FSI_GPIO_CRC_SIZE);

	local_irq_restore(flags);

	/* we have a whole message now; check CRC */
	crc = crc4(0, 1, 1);
	crc = crc4(crc, msg.msg, msg.bits);
	if (crc) {
		/* Check if it's all 1's, that probably means the host is off */
		if (((~msg.msg) & ((1ull << msg.bits) - 1)) == 0)
			return -ENODEV;
		dev_dbg(master->dev, "ERR response CRC msg: 0x%016llx (%d bits)\n",
			msg.msg, msg.bits);
		return -EAGAIN;
	}

	if (msgp)
		*msgp = msg;
	if (tagp)
		*tagp = tag;

	return 0;
}

static int issue_term(struct fsi_master_gpio *master, uint8_t slave)
{
	struct fsi_gpio_msg cmd;
	unsigned long flags;
	uint8_t tag;
	int rc;

	build_term_command(&cmd, slave);

	local_irq_save(flags);
	serial_out(master, &cmd);
	echo_delay(master);
	local_irq_restore(flags);

	rc = read_one_response(master, 0, NULL, &tag);
	if (rc < 0) {
		dev_err(master->dev,
				"TERM failed; lost communication with slave\n");
		return -EIO;
	} else if (tag != FSI_GPIO_RESP_ACK) {
		dev_err(master->dev, "TERM failed; response %d\n", tag);
		return -EIO;
	}

	return 0;
}

static int poll_for_response(struct fsi_master_gpio *master,
		uint8_t slave, uint8_t size, void *data)
{
	struct fsi_gpio_msg response, cmd;
	int busy_count = 0, rc, i;
	unsigned long flags;
	uint8_t tag;
	uint8_t *data_byte = data;
	int crc_err_retries = 0;
retry:
	rc = read_one_response(master, size, &response, &tag);

	/* Handle retries on CRC errors */
	if (rc == -EAGAIN) {
		/* Too many retries ? */
		if (crc_err_retries++ > FSI_CRC_ERR_RETRIES) {
			/*
			 * Pass it up as a -EIO otherwise upper level will retry
			 * the whole command which isn't what we want here.
			 */
			rc = -EIO;
			goto fail;
		}
		dev_dbg(master->dev,
			 "CRC error retry %d\n", crc_err_retries);
		trace_fsi_master_gpio_crc_rsp_error(master);
		build_epoll_command(&cmd, slave);
		local_irq_save(flags);
		clock_zeros(master, FSI_GPIO_EPOLL_CLOCKS);
		serial_out(master, &cmd);
		echo_delay(master);
		local_irq_restore(flags);
		goto retry;
	} else if (rc)
		goto fail;

	switch (tag) {
	case FSI_GPIO_RESP_ACK:
		if (size && data) {
			uint64_t val = response.msg;
			/* clear crc & mask */
			val >>= 4;
			val &= (1ull << (size * 8)) - 1;

			for (i = 0; i < size; i++) {
				data_byte[size-i-1] = val;
				val >>= 8;
			}
		}
		break;
	case FSI_GPIO_RESP_BUSY:
		/*
		 * Its necessary to clock slave before issuing
		 * d-poll, not indicated in the hardware protocol
		 * spec. < 20 clocks causes slave to hang, 21 ok.
		 */
		if (busy_count++ < FSI_GPIO_MAX_BUSY) {
			build_dpoll_command(&cmd, slave);
			local_irq_save(flags);
			clock_zeros(master, FSI_GPIO_DPOLL_CLOCKS);
			serial_out(master, &cmd);
			echo_delay(master);
			local_irq_restore(flags);
			goto retry;
		}
		dev_warn(master->dev,
			"ERR slave is stuck in busy state, issuing TERM\n");
		local_irq_save(flags);
		clock_zeros(master, FSI_GPIO_DPOLL_CLOCKS);
		local_irq_restore(flags);
		issue_term(master, slave);
		rc = -EIO;
		break;

	case FSI_GPIO_RESP_ERRA:
		dev_dbg(master->dev, "ERRA received: 0x%x\n", (int)response.msg);
		rc = -EIO;
		break;
	case FSI_GPIO_RESP_ERRC:
		dev_dbg(master->dev, "ERRC received: 0x%x\n", (int)response.msg);
		trace_fsi_master_gpio_crc_cmd_error(master);
		rc = -EAGAIN;
		break;
	}

	if (busy_count > 0)
		trace_fsi_master_gpio_poll_response_busy(master, busy_count);
 fail:
	/*
	 * tSendDelay clocks, avoids signal reflections when switching
	 * from receive of response back to send of data.
	 */
	local_irq_save(flags);
	clock_zeros(master, master->t_send_delay);
	local_irq_restore(flags);

	return rc;
}

static int send_request(struct fsi_master_gpio *master,
		struct fsi_gpio_msg *cmd)
{
	unsigned long flags;

	if (master->external_mode)
		return -EBUSY;

	local_irq_save(flags);
	serial_out(master, cmd);
	echo_delay(master);
	local_irq_restore(flags);

	return 0;
}

static int fsi_master_gpio_xfer(struct fsi_master_gpio *master, uint8_t slave,
		struct fsi_gpio_msg *cmd, size_t resp_len, void *resp)
{
	int rc = -EAGAIN, retries = 0;

	while ((retries++) < FSI_CRC_ERR_RETRIES) {
		rc = send_request(master, cmd);
		if (rc)
			break;
		rc = poll_for_response(master, slave, resp_len, resp);
		if (rc != -EAGAIN)
			break;
		rc = -EIO;
		dev_warn(master->dev, "ECRC retry %d\n", retries);

		/* Pace it a bit before retry */
		msleep(1);
	}

	return rc;
}

static int fsi_master_gpio_read(struct fsi_master *_master, int link,
		uint8_t id, uint32_t addr, void *val, size_t size)
{
	struct fsi_master_gpio *master = to_fsi_master_gpio(_master);
	struct fsi_gpio_msg cmd;
	int rc;

	if (link != 0)
		return -ENODEV;

	mutex_lock(&master->cmd_lock);
	build_ar_command(master, &cmd, id, addr, size, NULL);
	rc = fsi_master_gpio_xfer(master, id, &cmd, size, val);
	last_address_update(master, id, rc == 0, addr);
	mutex_unlock(&master->cmd_lock);

	return rc;
}

static int fsi_master_gpio_write(struct fsi_master *_master, int link,
		uint8_t id, uint32_t addr, const void *val, size_t size)
{
	struct fsi_master_gpio *master = to_fsi_master_gpio(_master);
	struct fsi_gpio_msg cmd;
	int rc;

	if (link != 0)
		return -ENODEV;

	mutex_lock(&master->cmd_lock);
	build_ar_command(master, &cmd, id, addr, size, val);
	rc = fsi_master_gpio_xfer(master, id, &cmd, 0, NULL);
	last_address_update(master, id, rc == 0, addr);
	mutex_unlock(&master->cmd_lock);

	return rc;
}

static int fsi_master_gpio_term(struct fsi_master *_master,
		int link, uint8_t id)
{
	struct fsi_master_gpio *master = to_fsi_master_gpio(_master);
	struct fsi_gpio_msg cmd;
	int rc;

	if (link != 0)
		return -ENODEV;

	mutex_lock(&master->cmd_lock);
	build_term_command(&cmd, id);
	rc = fsi_master_gpio_xfer(master, id, &cmd, 0, NULL);
	last_address_update(master, id, false, 0);
	mutex_unlock(&master->cmd_lock);

	return rc;
}

static int fsi_master_gpio_break(struct fsi_master *_master, int link)
{
	struct fsi_master_gpio *master = to_fsi_master_gpio(_master);
	unsigned long flags;

	if (link != 0)
		return -ENODEV;

	trace_fsi_master_gpio_break(master);

	mutex_lock(&master->cmd_lock);
	if (master->external_mode) {
		mutex_unlock(&master->cmd_lock);
		return -EBUSY;
	}

	local_irq_save(flags);

	set_sda_output(master, 1);
	sda_out(master, 1);
	clock_toggle(master, FSI_PRE_BREAK_CLOCKS);
	sda_out(master, 0);
	clock_toggle(master, FSI_BREAK_CLOCKS);
	echo_delay(master);
	sda_out(master, 1);
	clock_toggle(master, FSI_POST_BREAK_CLOCKS);

	local_irq_restore(flags);

	last_address_update(master, 0, false, 0);
	mutex_unlock(&master->cmd_lock);

	/* Wait for logic reset to take effect */
	udelay(200);

	return 0;
}

static void fsi_master_gpio_init(struct fsi_master_gpio *master)
{
	unsigned long flags;

	gpiod_direction_output(master->gpio_mux, 1);
	gpiod_direction_output(master->gpio_trans, 1);
	gpiod_direction_output(master->gpio_enable, 1);
	gpiod_direction_output(master->gpio_clk, 1);
	gpiod_direction_output(master->gpio_data, 1);

	/* todo: evaluate if clocks can be reduced */
	local_irq_save(flags);
	clock_zeros(master, FSI_INIT_CLOCKS);
	local_irq_restore(flags);
}

static void fsi_master_gpio_init_external(struct fsi_master_gpio *master)
{
	gpiod_direction_output(master->gpio_mux, 0);
	gpiod_direction_output(master->gpio_trans, 0);
	gpiod_direction_output(master->gpio_enable, 1);
	gpiod_direction_input(master->gpio_clk);
	gpiod_direction_input(master->gpio_data);
}

static int fsi_master_gpio_link_enable(struct fsi_master *_master, int link)
{
	struct fsi_master_gpio *master = to_fsi_master_gpio(_master);
	int rc = -EBUSY;

	if (link != 0)
		return -ENODEV;

	mutex_lock(&master->cmd_lock);
	if (!master->external_mode) {
		gpiod_set_value(master->gpio_enable, 1);
		rc = 0;
	}
	mutex_unlock(&master->cmd_lock);

	return rc;
}

static int fsi_master_gpio_link_config(struct fsi_master *_master, int link,
				       u8 t_send_delay, u8 t_echo_delay)
{
	struct fsi_master_gpio *master = to_fsi_master_gpio(_master);

	if (link != 0)
		return -ENODEV;

	mutex_lock(&master->cmd_lock);
	master->t_send_delay = t_send_delay;
	master->t_echo_delay = t_echo_delay;
	mutex_unlock(&master->cmd_lock);

	return 0;
}

static ssize_t external_mode_show(struct device *dev,
		struct device_attribute *attr, char *buf)
{
	struct fsi_master_gpio *master = dev_get_drvdata(dev);

	return snprintf(buf, PAGE_SIZE - 1, "%u\n",
			master->external_mode ? 1 : 0);
}

static ssize_t external_mode_store(struct device *dev,
		struct device_attribute *attr, const char *buf, size_t count)
{
	struct fsi_master_gpio *master = dev_get_drvdata(dev);
	unsigned long val;
	bool external_mode;
	int err;

	err = kstrtoul(buf, 0, &val);
	if (err)
		return err;

	external_mode = !!val;

	mutex_lock(&master->cmd_lock);

	if (external_mode == master->external_mode) {
		mutex_unlock(&master->cmd_lock);
		return count;
	}

	master->external_mode = external_mode;
	if (master->external_mode)
		fsi_master_gpio_init_external(master);
	else
		fsi_master_gpio_init(master);

	mutex_unlock(&master->cmd_lock);

	fsi_master_rescan(&master->master);

	return count;
}

static DEVICE_ATTR(external_mode, 0664,
		external_mode_show, external_mode_store);

static int fsi_master_gpio_probe(struct platform_device *pdev)
{
	struct fsi_master_gpio *master;
	struct gpio_desc *gpio;
	int rc;

	master = devm_kzalloc(&pdev->dev, sizeof(*master), GFP_KERNEL);
	if (!master)
		return -ENOMEM;

	master->dev = &pdev->dev;
	master->master.dev.parent = master->dev;
	master->master.dev.of_node = of_node_get(dev_of_node(master->dev));
	master->last_addr = LAST_ADDR_INVALID;

	gpio = devm_gpiod_get(&pdev->dev, "clock", 0);
	if (IS_ERR(gpio)) {
		dev_err(&pdev->dev, "failed to get clock gpio\n");
		return PTR_ERR(gpio);
	}
	master->gpio_clk = gpio;

	gpio = devm_gpiod_get(&pdev->dev, "data", 0);
	if (IS_ERR(gpio)) {
		dev_err(&pdev->dev, "failed to get data gpio\n");
		return PTR_ERR(gpio);
	}
	master->gpio_data = gpio;

	/* Optional GPIOs */
	gpio = devm_gpiod_get_optional(&pdev->dev, "trans", 0);
	if (IS_ERR(gpio)) {
		dev_err(&pdev->dev, "failed to get trans gpio\n");
		return PTR_ERR(gpio);
	}
	master->gpio_trans = gpio;

	gpio = devm_gpiod_get_optional(&pdev->dev, "enable", 0);
	if (IS_ERR(gpio)) {
		dev_err(&pdev->dev, "failed to get enable gpio\n");
		return PTR_ERR(gpio);
	}
	master->gpio_enable = gpio;

	gpio = devm_gpiod_get_optional(&pdev->dev, "mux", 0);
	if (IS_ERR(gpio)) {
		dev_err(&pdev->dev, "failed to get mux gpio\n");
		return PTR_ERR(gpio);
	}
	master->gpio_mux = gpio;

	/*
	 * Check if GPIO block is slow enought that no extra delays
	 * are necessary. This improves performance on ast2500 by
	 * an order of magnitude.
	 */
	master->no_delays = device_property_present(&pdev->dev, "no-gpio-delays");

	/* Default FSI command delays */
	master->t_send_delay = FSI_SEND_DELAY_CLOCKS;
	master->t_echo_delay = FSI_ECHO_DELAY_CLOCKS;

	master->master.n_links = 1;
	master->master.flags = FSI_MASTER_FLAG_SWCLOCK;
	master->master.read = fsi_master_gpio_read;
	master->master.write = fsi_master_gpio_write;
	master->master.term = fsi_master_gpio_term;
	master->master.send_break = fsi_master_gpio_break;
	master->master.link_enable = fsi_master_gpio_link_enable;
	master->master.link_config = fsi_master_gpio_link_config;
	platform_set_drvdata(pdev, master);
	mutex_init(&master->cmd_lock);

	fsi_master_gpio_init(master);

	rc = device_create_file(&pdev->dev, &dev_attr_external_mode);
	if (rc)
		return rc;

	return fsi_master_register(&master->master);
}


static int fsi_master_gpio_remove(struct platform_device *pdev)
{
	struct fsi_master_gpio *master = platform_get_drvdata(pdev);

	devm_gpiod_put(&pdev->dev, master->gpio_clk);
	devm_gpiod_put(&pdev->dev, master->gpio_data);
	if (master->gpio_trans)
		devm_gpiod_put(&pdev->dev, master->gpio_trans);
	if (master->gpio_enable)
		devm_gpiod_put(&pdev->dev, master->gpio_enable);
	if (master->gpio_mux)
		devm_gpiod_put(&pdev->dev, master->gpio_mux);
	fsi_master_unregister(&master->master);

	of_node_put(master->master.dev.of_node);

	return 0;
}

static const struct of_device_id fsi_master_gpio_match[] = {
	{ .compatible = "fsi-master-gpio" },
	{ },
};

static struct platform_driver fsi_master_gpio_driver = {
	.driver = {
		.name		= "fsi-master-gpio",
		.of_match_table	= fsi_master_gpio_match,
	},
	.probe	= fsi_master_gpio_probe,
	.remove = fsi_master_gpio_remove,
};

module_platform_driver(fsi_master_gpio_driver);
MODULE_LICENSE("GPL");