summaryrefslogtreecommitdiff
path: root/drivers/spi/spi-bcm2835.c
blob: e7874a6171ecdb4b5b5e7c99bb706aaca2135e2d (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
/*
 * Driver for Broadcom BCM2835 SPI Controllers
 *
 * Copyright (C) 2012 Chris Boot
 * Copyright (C) 2013 Stephen Warren
 * Copyright (C) 2015 Martin Sperl
 *
 * This driver is inspired by:
 * spi-ath79.c, Copyright (C) 2009-2011 Gabor Juhos <juhosg@openwrt.org>
 * spi-atmel.c, Copyright (C) 2006 Atmel Corporation
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 */

#include <asm/page.h>
#include <linux/clk.h>
#include <linux/completion.h>
#include <linux/delay.h>
#include <linux/dma-mapping.h>
#include <linux/dmaengine.h>
#include <linux/err.h>
#include <linux/interrupt.h>
#include <linux/io.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/of.h>
#include <linux/of_address.h>
#include <linux/of_device.h>
#include <linux/of_gpio.h>
#include <linux/of_irq.h>
#include <linux/spi/spi.h>

/* SPI register offsets */
#define BCM2835_SPI_CS			0x00
#define BCM2835_SPI_FIFO		0x04
#define BCM2835_SPI_CLK			0x08
#define BCM2835_SPI_DLEN		0x0c
#define BCM2835_SPI_LTOH		0x10
#define BCM2835_SPI_DC			0x14

/* Bitfields in CS */
#define BCM2835_SPI_CS_LEN_LONG		0x02000000
#define BCM2835_SPI_CS_DMA_LEN		0x01000000
#define BCM2835_SPI_CS_CSPOL2		0x00800000
#define BCM2835_SPI_CS_CSPOL1		0x00400000
#define BCM2835_SPI_CS_CSPOL0		0x00200000
#define BCM2835_SPI_CS_RXF		0x00100000
#define BCM2835_SPI_CS_RXR		0x00080000
#define BCM2835_SPI_CS_TXD		0x00040000
#define BCM2835_SPI_CS_RXD		0x00020000
#define BCM2835_SPI_CS_DONE		0x00010000
#define BCM2835_SPI_CS_LEN		0x00002000
#define BCM2835_SPI_CS_REN		0x00001000
#define BCM2835_SPI_CS_ADCS		0x00000800
#define BCM2835_SPI_CS_INTR		0x00000400
#define BCM2835_SPI_CS_INTD		0x00000200
#define BCM2835_SPI_CS_DMAEN		0x00000100
#define BCM2835_SPI_CS_TA		0x00000080
#define BCM2835_SPI_CS_CSPOL		0x00000040
#define BCM2835_SPI_CS_CLEAR_RX		0x00000020
#define BCM2835_SPI_CS_CLEAR_TX		0x00000010
#define BCM2835_SPI_CS_CPOL		0x00000008
#define BCM2835_SPI_CS_CPHA		0x00000004
#define BCM2835_SPI_CS_CS_10		0x00000002
#define BCM2835_SPI_CS_CS_01		0x00000001

#define BCM2835_SPI_POLLING_LIMIT_US	30
#define BCM2835_SPI_POLLING_JIFFIES	2
#define BCM2835_SPI_DMA_MIN_LENGTH	96
#define BCM2835_SPI_MODE_BITS	(SPI_CPOL | SPI_CPHA | SPI_CS_HIGH \
				| SPI_NO_CS | SPI_3WIRE)

#define DRV_NAME	"spi-bcm2835"

struct bcm2835_spi {
	void __iomem *regs;
	struct clk *clk;
	int irq;
	const u8 *tx_buf;
	u8 *rx_buf;
	int tx_len;
	int rx_len;
	bool dma_pending;
};

static inline u32 bcm2835_rd(struct bcm2835_spi *bs, unsigned reg)
{
	return readl(bs->regs + reg);
}

static inline void bcm2835_wr(struct bcm2835_spi *bs, unsigned reg, u32 val)
{
	writel(val, bs->regs + reg);
}

static inline void bcm2835_rd_fifo(struct bcm2835_spi *bs)
{
	u8 byte;

	while ((bs->rx_len) &&
	       (bcm2835_rd(bs, BCM2835_SPI_CS) & BCM2835_SPI_CS_RXD)) {
		byte = bcm2835_rd(bs, BCM2835_SPI_FIFO);
		if (bs->rx_buf)
			*bs->rx_buf++ = byte;
		bs->rx_len--;
	}
}

static inline void bcm2835_wr_fifo(struct bcm2835_spi *bs)
{
	u8 byte;

	while ((bs->tx_len) &&
	       (bcm2835_rd(bs, BCM2835_SPI_CS) & BCM2835_SPI_CS_TXD)) {
		byte = bs->tx_buf ? *bs->tx_buf++ : 0;
		bcm2835_wr(bs, BCM2835_SPI_FIFO, byte);
		bs->tx_len--;
	}
}

static void bcm2835_spi_reset_hw(struct spi_master *master)
{
	struct bcm2835_spi *bs = spi_master_get_devdata(master);
	u32 cs = bcm2835_rd(bs, BCM2835_SPI_CS);

	/* Disable SPI interrupts and transfer */
	cs &= ~(BCM2835_SPI_CS_INTR |
		BCM2835_SPI_CS_INTD |
		BCM2835_SPI_CS_DMAEN |
		BCM2835_SPI_CS_TA);
	/* and reset RX/TX FIFOS */
	cs |= BCM2835_SPI_CS_CLEAR_RX | BCM2835_SPI_CS_CLEAR_TX;

	/* and reset the SPI_HW */
	bcm2835_wr(bs, BCM2835_SPI_CS, cs);
	/* as well as DLEN */
	bcm2835_wr(bs, BCM2835_SPI_DLEN, 0);
}

static irqreturn_t bcm2835_spi_interrupt(int irq, void *dev_id)
{
	struct spi_master *master = dev_id;
	struct bcm2835_spi *bs = spi_master_get_devdata(master);

	/* Read as many bytes as possible from FIFO */
	bcm2835_rd_fifo(bs);
	/* Write as many bytes as possible to FIFO */
	bcm2835_wr_fifo(bs);

	/* based on flags decide if we can finish the transfer */
	if (bcm2835_rd(bs, BCM2835_SPI_CS) & BCM2835_SPI_CS_DONE) {
		/* Transfer complete - reset SPI HW */
		bcm2835_spi_reset_hw(master);
		/* wake up the framework */
		complete(&master->xfer_completion);
	}

	return IRQ_HANDLED;
}

static int bcm2835_spi_transfer_one_irq(struct spi_master *master,
					struct spi_device *spi,
					struct spi_transfer *tfr,
					u32 cs)
{
	struct bcm2835_spi *bs = spi_master_get_devdata(master);

	/* fill in fifo if we have gpio-cs
	 * note that there have been rare events where the native-CS
	 * flapped for <1us which may change the behaviour
	 * with gpio-cs this does not happen, so it is implemented
	 * only for this case
	 */
	if (gpio_is_valid(spi->cs_gpio)) {
		/* enable HW block, but without interrupts enabled
		 * this would triggern an immediate interrupt
		 */
		bcm2835_wr(bs, BCM2835_SPI_CS,
			   cs | BCM2835_SPI_CS_TA);
		/* fill in tx fifo as much as possible */
		bcm2835_wr_fifo(bs);
	}

	/*
	 * Enable the HW block. This will immediately trigger a DONE (TX
	 * empty) interrupt, upon which we will fill the TX FIFO with the
	 * first TX bytes. Pre-filling the TX FIFO here to avoid the
	 * interrupt doesn't work:-(
	 */
	cs |= BCM2835_SPI_CS_INTR | BCM2835_SPI_CS_INTD | BCM2835_SPI_CS_TA;
	bcm2835_wr(bs, BCM2835_SPI_CS, cs);

	/* signal that we need to wait for completion */
	return 1;
}

/*
 * DMA support
 *
 * this implementation has currently a few issues in so far as it does
 * not work arrount limitations of the HW.
 *
 * the main one being that DMA transfers are limited to 16 bit
 * (so 0 to 65535 bytes) by the SPI HW due to BCM2835_SPI_DLEN
 *
 * also we currently assume that the scatter-gather fragments are
 * all multiple of 4 (except the last) - otherwise we would need
 * to reset the FIFO before subsequent transfers...
 * this also means that tx/rx transfers sg's need to be of equal size!
 *
 * there may be a few more border-cases we may need to address as well
 * but unfortunately this would mean splitting up the scatter-gather
 * list making it slightly unpractical...
 */
static void bcm2835_spi_dma_done(void *data)
{
	struct spi_master *master = data;
	struct bcm2835_spi *bs = spi_master_get_devdata(master);

	/* reset fifo and HW */
	bcm2835_spi_reset_hw(master);

	/* and terminate tx-dma as we do not have an irq for it
	 * because when the rx dma will terminate and this callback
	 * is called the tx-dma must have finished - can't get to this
	 * situation otherwise...
	 */
	dmaengine_terminate_all(master->dma_tx);

	/* mark as no longer pending */
	bs->dma_pending = 0;

	/* and mark as completed */;
	complete(&master->xfer_completion);
}

static int bcm2835_spi_prepare_sg(struct spi_master *master,
				  struct spi_transfer *tfr,
				  bool is_tx)
{
	struct dma_chan *chan;
	struct scatterlist *sgl;
	unsigned int nents;
	enum dma_transfer_direction dir;
	unsigned long flags;

	struct dma_async_tx_descriptor *desc;
	dma_cookie_t cookie;

	if (is_tx) {
		dir   = DMA_MEM_TO_DEV;
		chan  = master->dma_tx;
		nents = tfr->tx_sg.nents;
		sgl   = tfr->tx_sg.sgl;
		flags = 0 /* no  tx interrupt */;

	} else {
		dir   = DMA_DEV_TO_MEM;
		chan  = master->dma_rx;
		nents = tfr->rx_sg.nents;
		sgl   = tfr->rx_sg.sgl;
		flags = DMA_PREP_INTERRUPT;
	}
	/* prepare the channel */
	desc = dmaengine_prep_slave_sg(chan, sgl, nents, dir, flags);
	if (!desc)
		return -EINVAL;

	/* set callback for rx */
	if (!is_tx) {
		desc->callback = bcm2835_spi_dma_done;
		desc->callback_param = master;
	}

	/* submit it to DMA-engine */
	cookie = dmaengine_submit(desc);

	return dma_submit_error(cookie);
}

static inline int bcm2835_check_sg_length(struct sg_table *sgt)
{
	int i;
	struct scatterlist *sgl;

	/* check that the sg entries are word-sized (except for last) */
	for_each_sg(sgt->sgl, sgl, (int)sgt->nents - 1, i) {
		if (sg_dma_len(sgl) % 4)
			return -EFAULT;
	}

	return 0;
}

static int bcm2835_spi_transfer_one_dma(struct spi_master *master,
					struct spi_device *spi,
					struct spi_transfer *tfr,
					u32 cs)
{
	struct bcm2835_spi *bs = spi_master_get_devdata(master);
	int ret;

	/* check that the scatter gather segments are all a multiple of 4 */
	if (bcm2835_check_sg_length(&tfr->tx_sg) ||
	    bcm2835_check_sg_length(&tfr->rx_sg)) {
		dev_warn_once(&spi->dev,
			      "scatter gather segment length is not a multiple of 4 - falling back to interrupt mode\n");
		return bcm2835_spi_transfer_one_irq(master, spi, tfr, cs);
	}

	/* setup tx-DMA */
	ret = bcm2835_spi_prepare_sg(master, tfr, true);
	if (ret)
		return ret;

	/* start TX early */
	dma_async_issue_pending(master->dma_tx);

	/* mark as dma pending */
	bs->dma_pending = 1;

	/* set the DMA length */
	bcm2835_wr(bs, BCM2835_SPI_DLEN, tfr->len);

	/* start the HW */
	bcm2835_wr(bs, BCM2835_SPI_CS,
		   cs | BCM2835_SPI_CS_TA | BCM2835_SPI_CS_DMAEN);

	/* setup rx-DMA late - to run transfers while
	 * mapping of the rx buffers still takes place
	 * this saves 10us or more.
	 */
	ret = bcm2835_spi_prepare_sg(master, tfr, false);
	if (ret) {
		/* need to reset on errors */
		dmaengine_terminate_all(master->dma_tx);
		bcm2835_spi_reset_hw(master);
		return ret;
	}

	/* start rx dma late */
	dma_async_issue_pending(master->dma_rx);

	/* wait for wakeup in framework */
	return 1;
}

static bool bcm2835_spi_can_dma(struct spi_master *master,
				struct spi_device *spi,
				struct spi_transfer *tfr)
{
	/* only run for gpio_cs */
	if (!gpio_is_valid(spi->cs_gpio))
		return false;

	/* we start DMA efforts only on bigger transfers */
	if (tfr->len < BCM2835_SPI_DMA_MIN_LENGTH)
		return false;

	/* BCM2835_SPI_DLEN has defined a max transfer size as
	 * 16 bit, so max is 65535
	 * we can revisit this by using an alternative transfer
	 * method - ideally this would get done without any more
	 * interaction...
	 */
	if (tfr->len > 65535) {
		dev_warn_once(&spi->dev,
			      "transfer size of %d too big for dma-transfer\n",
			      tfr->len);
		return false;
	}

	/* if we run rx/tx_buf with word aligned addresses then we are OK */
	if ((((size_t)tfr->rx_buf & 3) == 0) &&
	    (((size_t)tfr->tx_buf & 3) == 0))
		return true;

	/* otherwise we only allow transfers within the same page
	 * to avoid wasting time on dma_mapping when it is not practical
	 */
	if (((size_t)tfr->tx_buf & PAGE_MASK) + tfr->len > PAGE_SIZE) {
		dev_warn_once(&spi->dev,
			      "Unaligned spi tx-transfer bridging page\n");
		return false;
	}
	if (((size_t)tfr->rx_buf & PAGE_MASK) + tfr->len > PAGE_SIZE) {
		dev_warn_once(&spi->dev,
			      "Unaligned spi tx-transfer bridging page\n");
		return false;
	}

	/* return OK */
	return true;
}

static void bcm2835_dma_release(struct spi_master *master)
{
	if (master->dma_tx) {
		dmaengine_terminate_all(master->dma_tx);
		dma_release_channel(master->dma_tx);
		master->dma_tx = NULL;
	}
	if (master->dma_rx) {
		dmaengine_terminate_all(master->dma_rx);
		dma_release_channel(master->dma_rx);
		master->dma_rx = NULL;
	}
}

static void bcm2835_dma_init(struct spi_master *master, struct device *dev)
{
	struct dma_slave_config slave_config;
	const __be32 *addr;
	dma_addr_t dma_reg_base;
	int ret;

	/* base address in dma-space */
	addr = of_get_address(master->dev.of_node, 0, NULL, NULL);
	if (!addr) {
		dev_err(dev, "could not get DMA-register address - not using dma mode\n");
		goto err;
	}
	dma_reg_base = be32_to_cpup(addr);

	/* get tx/rx dma */
	master->dma_tx = dma_request_slave_channel(dev, "tx");
	if (!master->dma_tx) {
		dev_err(dev, "no tx-dma configuration found - not using dma mode\n");
		goto err;
	}
	master->dma_rx = dma_request_slave_channel(dev, "rx");
	if (!master->dma_rx) {
		dev_err(dev, "no rx-dma configuration found - not using dma mode\n");
		goto err_release;
	}

	/* configure DMAs */
	slave_config.direction = DMA_MEM_TO_DEV;
	slave_config.dst_addr = (u32)(dma_reg_base + BCM2835_SPI_FIFO);
	slave_config.dst_addr_width = DMA_SLAVE_BUSWIDTH_4_BYTES;

	ret = dmaengine_slave_config(master->dma_tx, &slave_config);
	if (ret)
		goto err_config;

	slave_config.direction = DMA_DEV_TO_MEM;
	slave_config.src_addr = (u32)(dma_reg_base + BCM2835_SPI_FIFO);
	slave_config.src_addr_width = DMA_SLAVE_BUSWIDTH_4_BYTES;

	ret = dmaengine_slave_config(master->dma_rx, &slave_config);
	if (ret)
		goto err_config;

	/* all went well, so set can_dma */
	master->can_dma = bcm2835_spi_can_dma;
	master->max_dma_len = 65535; /* limitation by BCM2835_SPI_DLEN */
	/* need to do TX AND RX DMA, so we need dummy buffers */
	master->flags = SPI_MASTER_MUST_RX | SPI_MASTER_MUST_TX;

	return;

err_config:
	dev_err(dev, "issue configuring dma: %d - not using DMA mode\n",
		ret);
err_release:
	bcm2835_dma_release(master);
err:
	return;
}

static int bcm2835_spi_transfer_one_poll(struct spi_master *master,
					 struct spi_device *spi,
					 struct spi_transfer *tfr,
					 u32 cs,
					 unsigned long long xfer_time_us)
{
	struct bcm2835_spi *bs = spi_master_get_devdata(master);
	unsigned long timeout;

	/* enable HW block without interrupts */
	bcm2835_wr(bs, BCM2835_SPI_CS, cs | BCM2835_SPI_CS_TA);

	/* fill in the fifo before timeout calculations
	 * if we are interrupted here, then the data is
	 * getting transferred by the HW while we are interrupted
	 */
	bcm2835_wr_fifo(bs);

	/* set the timeout */
	timeout = jiffies + BCM2835_SPI_POLLING_JIFFIES;

	/* loop until finished the transfer */
	while (bs->rx_len) {
		/* fill in tx fifo with remaining data */
		bcm2835_wr_fifo(bs);

		/* read from fifo as much as possible */
		bcm2835_rd_fifo(bs);

		/* if there is still data pending to read
		 * then check the timeout
		 */
		if (bs->rx_len && time_after(jiffies, timeout)) {
			dev_dbg_ratelimited(&spi->dev,
					    "timeout period reached: jiffies: %lu remaining tx/rx: %d/%d - falling back to interrupt mode\n",
					    jiffies - timeout,
					    bs->tx_len, bs->rx_len);
			/* fall back to interrupt mode */
			return bcm2835_spi_transfer_one_irq(master, spi,
							    tfr, cs);
		}
	}

	/* Transfer complete - reset SPI HW */
	bcm2835_spi_reset_hw(master);
	/* and return without waiting for completion */
	return 0;
}

static int bcm2835_spi_transfer_one(struct spi_master *master,
				    struct spi_device *spi,
				    struct spi_transfer *tfr)
{
	struct bcm2835_spi *bs = spi_master_get_devdata(master);
	unsigned long spi_hz, clk_hz, cdiv;
	unsigned long spi_used_hz;
	unsigned long long xfer_time_us;
	u32 cs = bcm2835_rd(bs, BCM2835_SPI_CS);

	/* set clock */
	spi_hz = tfr->speed_hz;
	clk_hz = clk_get_rate(bs->clk);

	if (spi_hz >= clk_hz / 2) {
		cdiv = 2; /* clk_hz/2 is the fastest we can go */
	} else if (spi_hz) {
		/* CDIV must be a multiple of two */
		cdiv = DIV_ROUND_UP(clk_hz, spi_hz);
		cdiv += (cdiv % 2);

		if (cdiv >= 65536)
			cdiv = 0; /* 0 is the slowest we can go */
	} else {
		cdiv = 0; /* 0 is the slowest we can go */
	}
	spi_used_hz = cdiv ? (clk_hz / cdiv) : (clk_hz / 65536);
	bcm2835_wr(bs, BCM2835_SPI_CLK, cdiv);

	/* handle all the 3-wire mode */
	if ((spi->mode & SPI_3WIRE) && (tfr->rx_buf))
		cs |= BCM2835_SPI_CS_REN;
	else
		cs &= ~BCM2835_SPI_CS_REN;

	/* for gpio_cs set dummy CS so that no HW-CS get changed
	 * we can not run this in bcm2835_spi_set_cs, as it does
	 * not get called for cs_gpio cases, so we need to do it here
	 */
	if (gpio_is_valid(spi->cs_gpio) || (spi->mode & SPI_NO_CS))
		cs |= BCM2835_SPI_CS_CS_10 | BCM2835_SPI_CS_CS_01;

	/* set transmit buffers and length */
	bs->tx_buf = tfr->tx_buf;
	bs->rx_buf = tfr->rx_buf;
	bs->tx_len = tfr->len;
	bs->rx_len = tfr->len;

	/* calculate the estimated time in us the transfer runs */
	xfer_time_us = (unsigned long long)tfr->len
		* 9 /* clocks/byte - SPI-HW waits 1 clock after each byte */
		* 1000000;
	do_div(xfer_time_us, spi_used_hz);

	/* for short requests run polling*/
	if (xfer_time_us <= BCM2835_SPI_POLLING_LIMIT_US)
		return bcm2835_spi_transfer_one_poll(master, spi, tfr,
						     cs, xfer_time_us);

	/* run in dma mode if conditions are right */
	if (master->can_dma && bcm2835_spi_can_dma(master, spi, tfr))
		return bcm2835_spi_transfer_one_dma(master, spi, tfr, cs);

	/* run in interrupt-mode */
	return bcm2835_spi_transfer_one_irq(master, spi, tfr, cs);
}

static int bcm2835_spi_prepare_message(struct spi_master *master,
				       struct spi_message *msg)
{
	struct spi_device *spi = msg->spi;
	struct bcm2835_spi *bs = spi_master_get_devdata(master);
	u32 cs = bcm2835_rd(bs, BCM2835_SPI_CS);

	cs &= ~(BCM2835_SPI_CS_CPOL | BCM2835_SPI_CS_CPHA);

	if (spi->mode & SPI_CPOL)
		cs |= BCM2835_SPI_CS_CPOL;
	if (spi->mode & SPI_CPHA)
		cs |= BCM2835_SPI_CS_CPHA;

	bcm2835_wr(bs, BCM2835_SPI_CS, cs);

	return 0;
}

static void bcm2835_spi_handle_err(struct spi_master *master,
				   struct spi_message *msg)
{
	struct bcm2835_spi *bs = spi_master_get_devdata(master);

	/* if an error occurred and we have an active dma, then terminate */
	if (bs->dma_pending) {
		dmaengine_terminate_all(master->dma_tx);
		dmaengine_terminate_all(master->dma_rx);
		bs->dma_pending = 0;
	}
	/* and reset */
	bcm2835_spi_reset_hw(master);
}

static void bcm2835_spi_set_cs(struct spi_device *spi, bool gpio_level)
{
	/*
	 * we can assume that we are "native" as per spi_set_cs
	 *   calling us ONLY when cs_gpio is not set
	 * we can also assume that we are CS < 3 as per bcm2835_spi_setup
	 *   we would not get called because of error handling there.
	 * the level passed is the electrical level not enabled/disabled
	 *   so it has to get translated back to enable/disable
	 *   see spi_set_cs in spi.c for the implementation
	 */

	struct spi_master *master = spi->master;
	struct bcm2835_spi *bs = spi_master_get_devdata(master);
	u32 cs = bcm2835_rd(bs, BCM2835_SPI_CS);
	bool enable;

	/* calculate the enable flag from the passed gpio_level */
	enable = (spi->mode & SPI_CS_HIGH) ? gpio_level : !gpio_level;

	/* set flags for "reverse" polarity in the registers */
	if (spi->mode & SPI_CS_HIGH) {
		/* set the correct CS-bits */
		cs |= BCM2835_SPI_CS_CSPOL;
		cs |= BCM2835_SPI_CS_CSPOL0 << spi->chip_select;
	} else {
		/* clean the CS-bits */
		cs &= ~BCM2835_SPI_CS_CSPOL;
		cs &= ~(BCM2835_SPI_CS_CSPOL0 << spi->chip_select);
	}

	/* select the correct chip_select depending on disabled/enabled */
	if (enable) {
		/* set cs correctly */
		if (spi->mode & SPI_NO_CS) {
			/* use the "undefined" chip-select */
			cs |= BCM2835_SPI_CS_CS_10 | BCM2835_SPI_CS_CS_01;
		} else {
			/* set the chip select */
			cs &= ~(BCM2835_SPI_CS_CS_10 | BCM2835_SPI_CS_CS_01);
			cs |= spi->chip_select;
		}
	} else {
		/* disable CSPOL which puts HW-CS into deselected state */
		cs &= ~BCM2835_SPI_CS_CSPOL;
		/* use the "undefined" chip-select as precaution */
		cs |= BCM2835_SPI_CS_CS_10 | BCM2835_SPI_CS_CS_01;
	}

	/* finally set the calculated flags in SPI_CS */
	bcm2835_wr(bs, BCM2835_SPI_CS, cs);
}

static int chip_match_name(struct gpio_chip *chip, void *data)
{
	return !strcmp(chip->label, data);
}

static int bcm2835_spi_setup(struct spi_device *spi)
{
	int err;
	struct gpio_chip *chip;
	/*
	 * sanity checking the native-chipselects
	 */
	if (spi->mode & SPI_NO_CS)
		return 0;
	if (gpio_is_valid(spi->cs_gpio))
		return 0;
	if (spi->chip_select > 1) {
		/* error in the case of native CS requested with CS > 1
		 * officially there is a CS2, but it is not documented
		 * which GPIO is connected with that...
		 */
		dev_err(&spi->dev,
			"setup: only two native chip-selects are supported\n");
		return -EINVAL;
	}
	/* now translate native cs to GPIO */

	/* get the gpio chip for the base */
	chip = gpiochip_find("pinctrl-bcm2835", chip_match_name);
	if (!chip)
		return 0;

	/* and calculate the real CS */
	spi->cs_gpio = chip->base + 8 - spi->chip_select;

	/* and set up the "mode" and level */
	dev_info(&spi->dev, "setting up native-CS%i as GPIO %i\n",
		 spi->chip_select, spi->cs_gpio);

	/* set up GPIO as output and pull to the correct level */
	err = gpio_direction_output(spi->cs_gpio,
				    (spi->mode & SPI_CS_HIGH) ? 0 : 1);
	if (err) {
		dev_err(&spi->dev,
			"could not set CS%i gpio %i as output: %i",
			spi->chip_select, spi->cs_gpio, err);
		return err;
	}
	/* the implementation of pinctrl-bcm2835 currently does not
	 * set the GPIO value when using gpio_direction_output
	 * so we are setting it here explicitly
	 */
	gpio_set_value(spi->cs_gpio, (spi->mode & SPI_CS_HIGH) ? 0 : 1);

	return 0;
}

static int bcm2835_spi_probe(struct platform_device *pdev)
{
	struct spi_master *master;
	struct bcm2835_spi *bs;
	struct resource *res;
	int err;

	master = spi_alloc_master(&pdev->dev, sizeof(*bs));
	if (!master) {
		dev_err(&pdev->dev, "spi_alloc_master() failed\n");
		return -ENOMEM;
	}

	platform_set_drvdata(pdev, master);

	master->mode_bits = BCM2835_SPI_MODE_BITS;
	master->bits_per_word_mask = SPI_BPW_MASK(8);
	master->num_chipselect = 3;
	master->setup = bcm2835_spi_setup;
	master->set_cs = bcm2835_spi_set_cs;
	master->transfer_one = bcm2835_spi_transfer_one;
	master->handle_err = bcm2835_spi_handle_err;
	master->prepare_message = bcm2835_spi_prepare_message;
	master->dev.of_node = pdev->dev.of_node;

	bs = spi_master_get_devdata(master);

	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
	bs->regs = devm_ioremap_resource(&pdev->dev, res);
	if (IS_ERR(bs->regs)) {
		err = PTR_ERR(bs->regs);
		goto out_master_put;
	}

	bs->clk = devm_clk_get(&pdev->dev, NULL);
	if (IS_ERR(bs->clk)) {
		err = PTR_ERR(bs->clk);
		dev_err(&pdev->dev, "could not get clk: %d\n", err);
		goto out_master_put;
	}

	bs->irq = irq_of_parse_and_map(pdev->dev.of_node, 0);
	if (bs->irq <= 0) {
		dev_err(&pdev->dev, "could not get IRQ: %d\n", bs->irq);
		err = bs->irq ? bs->irq : -ENODEV;
		goto out_master_put;
	}

	clk_prepare_enable(bs->clk);

	err = devm_request_irq(&pdev->dev, bs->irq, bcm2835_spi_interrupt, 0,
			       dev_name(&pdev->dev), master);
	if (err) {
		dev_err(&pdev->dev, "could not request IRQ: %d\n", err);
		goto out_clk_disable;
	}

	bcm2835_dma_init(master, &pdev->dev);

	/* initialise the hardware with the default polarities */
	bcm2835_wr(bs, BCM2835_SPI_CS,
		   BCM2835_SPI_CS_CLEAR_RX | BCM2835_SPI_CS_CLEAR_TX);

	err = devm_spi_register_master(&pdev->dev, master);
	if (err) {
		dev_err(&pdev->dev, "could not register SPI master: %d\n", err);
		goto out_clk_disable;
	}

	return 0;

out_clk_disable:
	clk_disable_unprepare(bs->clk);
out_master_put:
	spi_master_put(master);
	return err;
}

static int bcm2835_spi_remove(struct platform_device *pdev)
{
	struct spi_master *master = platform_get_drvdata(pdev);
	struct bcm2835_spi *bs = spi_master_get_devdata(master);

	/* Clear FIFOs, and disable the HW block */
	bcm2835_wr(bs, BCM2835_SPI_CS,
		   BCM2835_SPI_CS_CLEAR_RX | BCM2835_SPI_CS_CLEAR_TX);

	clk_disable_unprepare(bs->clk);

	bcm2835_dma_release(master);

	return 0;
}

static const struct of_device_id bcm2835_spi_match[] = {
	{ .compatible = "brcm,bcm2835-spi", },
	{}
};
MODULE_DEVICE_TABLE(of, bcm2835_spi_match);

static struct platform_driver bcm2835_spi_driver = {
	.driver		= {
		.name		= DRV_NAME,
		.of_match_table	= bcm2835_spi_match,
	},
	.probe		= bcm2835_spi_probe,
	.remove		= bcm2835_spi_remove,
};
module_platform_driver(bcm2835_spi_driver);

MODULE_DESCRIPTION("SPI controller driver for Broadcom BCM2835");
MODULE_AUTHOR("Chris Boot <bootc@bootc.net>");
MODULE_LICENSE("GPL v2");