summaryrefslogtreecommitdiff
path: root/drivers/spi/spi-gpio.c
blob: d8db4564b406ad146d0d607cb890da349ba59e12 (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
// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * SPI host driver using generic bitbanged GPIO
 *
 * Copyright (C) 2006,2008 David Brownell
 * Copyright (C) 2017 Linus Walleij
 */
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/platform_device.h>
#include <linux/gpio/consumer.h>
#include <linux/of.h>

#include <linux/spi/spi.h>
#include <linux/spi/spi_bitbang.h>
#include <linux/spi/spi_gpio.h>


/*
 * This bitbanging SPI host driver should help make systems usable
 * when a native hardware SPI engine is not available, perhaps because
 * its driver isn't yet working or because the I/O pins it requires
 * are used for other purposes.
 *
 * platform_device->driver_data ... points to spi_gpio
 *
 * spi->controller_state ... reserved for bitbang framework code
 *
 * spi->controller->dev.driver_data ... points to spi_gpio->bitbang
 */

struct spi_gpio {
	struct spi_bitbang		bitbang;
	struct gpio_desc		*sck;
	struct gpio_desc		*miso;
	struct gpio_desc		*mosi;
	struct gpio_desc		**cs_gpios;
};

/*----------------------------------------------------------------------*/

/*
 * Because the overhead of going through four GPIO procedure calls
 * per transferred bit can make performance a problem, this code
 * is set up so that you can use it in either of two ways:
 *
 *   - The slow generic way:  set up platform_data to hold the GPIO
 *     numbers used for MISO/MOSI/SCK, and issue procedure calls for
 *     each of them.  This driver can handle several such busses.
 *
 *   - The quicker inlined way:  only helps with platform GPIO code
 *     that inlines operations for constant GPIOs.  This can give
 *     you tight (fast!) inner loops, but each such bus needs a
 *     new driver.  You'll define a new C file, with Makefile and
 *     Kconfig support; the C code can be a total of six lines:
 *
 *		#define DRIVER_NAME	"myboard_spi2"
 *		#define	SPI_MISO_GPIO	119
 *		#define	SPI_MOSI_GPIO	120
 *		#define	SPI_SCK_GPIO	121
 *		#define	SPI_N_CHIPSEL	4
 *		#include "spi-gpio.c"
 */

#ifndef DRIVER_NAME
#define DRIVER_NAME	"spi_gpio"

#define GENERIC_BITBANG	/* vs tight inlines */

#endif

/*----------------------------------------------------------------------*/

static inline struct spi_gpio *__pure
spi_to_spi_gpio(const struct spi_device *spi)
{
	const struct spi_bitbang	*bang;
	struct spi_gpio			*spi_gpio;

	bang = spi_controller_get_devdata(spi->controller);
	spi_gpio = container_of(bang, struct spi_gpio, bitbang);
	return spi_gpio;
}

/* These helpers are in turn called by the bitbang inlines */
static inline void setsck(const struct spi_device *spi, int is_on)
{
	struct spi_gpio *spi_gpio = spi_to_spi_gpio(spi);

	gpiod_set_value_cansleep(spi_gpio->sck, is_on);
}

static inline void setmosi(const struct spi_device *spi, int is_on)
{
	struct spi_gpio *spi_gpio = spi_to_spi_gpio(spi);

	gpiod_set_value_cansleep(spi_gpio->mosi, is_on);
}

static inline int getmiso(const struct spi_device *spi)
{
	struct spi_gpio *spi_gpio = spi_to_spi_gpio(spi);

	if (spi->mode & SPI_3WIRE)
		return !!gpiod_get_value_cansleep(spi_gpio->mosi);
	else
		return !!gpiod_get_value_cansleep(spi_gpio->miso);
}

/*
 * NOTE:  this clocks "as fast as we can".  It "should" be a function of the
 * requested device clock.  Software overhead means we usually have trouble
 * reaching even one Mbit/sec (except when we can inline bitops), so for now
 * we'll just assume we never need additional per-bit slowdowns.
 */
#define spidelay(nsecs)	do {} while (0)

#include "spi-bitbang-txrx.h"

/*
 * These functions can leverage inline expansion of GPIO calls to shrink
 * costs for a txrx bit, often by factors of around ten (by instruction
 * count).  That is particularly visible for larger word sizes, but helps
 * even with default 8-bit words.
 *
 * REVISIT overheads calling these functions for each word also have
 * significant performance costs.  Having txrx_bufs() calls that inline
 * the txrx_word() logic would help performance, e.g. on larger blocks
 * used with flash storage or MMC/SD.  There should also be ways to make
 * GCC be less stupid about reloading registers inside the I/O loops,
 * even without inlined GPIO calls; __attribute__((hot)) on GCC 4.3?
 */

static u32 spi_gpio_txrx_word_mode0(struct spi_device *spi,
		unsigned nsecs, u32 word, u8 bits, unsigned flags)
{
	if (unlikely(spi->mode & SPI_LSB_FIRST))
		return bitbang_txrx_le_cpha0(spi, nsecs, 0, flags, word, bits);
	else
		return bitbang_txrx_be_cpha0(spi, nsecs, 0, flags, word, bits);
}

static u32 spi_gpio_txrx_word_mode1(struct spi_device *spi,
		unsigned nsecs, u32 word, u8 bits, unsigned flags)
{
	if (unlikely(spi->mode & SPI_LSB_FIRST))
		return bitbang_txrx_le_cpha1(spi, nsecs, 0, flags, word, bits);
	else
		return bitbang_txrx_be_cpha1(spi, nsecs, 0, flags, word, bits);
}

static u32 spi_gpio_txrx_word_mode2(struct spi_device *spi,
		unsigned nsecs, u32 word, u8 bits, unsigned flags)
{
	if (unlikely(spi->mode & SPI_LSB_FIRST))
		return bitbang_txrx_le_cpha0(spi, nsecs, 1, flags, word, bits);
	else
		return bitbang_txrx_be_cpha0(spi, nsecs, 1, flags, word, bits);
}

static u32 spi_gpio_txrx_word_mode3(struct spi_device *spi,
		unsigned nsecs, u32 word, u8 bits, unsigned flags)
{
	if (unlikely(spi->mode & SPI_LSB_FIRST))
		return bitbang_txrx_le_cpha1(spi, nsecs, 1, flags, word, bits);
	else
		return bitbang_txrx_be_cpha1(spi, nsecs, 1, flags, word, bits);
}

/*
 * These functions do not call setmosi or getmiso if respective flag
 * (SPI_CONTROLLER_NO_RX or SPI_CONTROLLER_NO_TX) is set, so they are safe to
 * call when such pin is not present or defined in the controller.
 * A separate set of callbacks is defined to get highest possible
 * speed in the generic case (when both MISO and MOSI lines are
 * available), as optimiser will remove the checks when argument is
 * constant.
 */

static u32 spi_gpio_spec_txrx_word_mode0(struct spi_device *spi,
		unsigned nsecs, u32 word, u8 bits, unsigned flags)
{
	flags = spi->controller->flags;
	if (unlikely(spi->mode & SPI_LSB_FIRST))
		return bitbang_txrx_le_cpha0(spi, nsecs, 0, flags, word, bits);
	else
		return bitbang_txrx_be_cpha0(spi, nsecs, 0, flags, word, bits);
}

static u32 spi_gpio_spec_txrx_word_mode1(struct spi_device *spi,
		unsigned nsecs, u32 word, u8 bits, unsigned flags)
{
	flags = spi->controller->flags;
	if (unlikely(spi->mode & SPI_LSB_FIRST))
		return bitbang_txrx_le_cpha1(spi, nsecs, 0, flags, word, bits);
	else
		return bitbang_txrx_be_cpha1(spi, nsecs, 0, flags, word, bits);
}

static u32 spi_gpio_spec_txrx_word_mode2(struct spi_device *spi,
		unsigned nsecs, u32 word, u8 bits, unsigned flags)
{
	flags = spi->controller->flags;
	if (unlikely(spi->mode & SPI_LSB_FIRST))
		return bitbang_txrx_le_cpha0(spi, nsecs, 1, flags, word, bits);
	else
		return bitbang_txrx_be_cpha0(spi, nsecs, 1, flags, word, bits);
}

static u32 spi_gpio_spec_txrx_word_mode3(struct spi_device *spi,
		unsigned nsecs, u32 word, u8 bits, unsigned flags)
{
	flags = spi->controller->flags;
	if (unlikely(spi->mode & SPI_LSB_FIRST))
		return bitbang_txrx_le_cpha1(spi, nsecs, 1, flags, word, bits);
	else
		return bitbang_txrx_be_cpha1(spi, nsecs, 1, flags, word, bits);
}

/*----------------------------------------------------------------------*/

static void spi_gpio_chipselect(struct spi_device *spi, int is_active)
{
	struct spi_gpio *spi_gpio = spi_to_spi_gpio(spi);

	/* set initial clock line level */
	if (is_active)
		gpiod_set_value_cansleep(spi_gpio->sck, spi->mode & SPI_CPOL);

	/* Drive chip select line, if we have one */
	if (spi_gpio->cs_gpios) {
		struct gpio_desc *cs = spi_gpio->cs_gpios[spi_get_chipselect(spi, 0)];

		/* SPI chip selects are normally active-low */
		gpiod_set_value_cansleep(cs, (spi->mode & SPI_CS_HIGH) ? is_active : !is_active);
	}
}

static int spi_gpio_setup(struct spi_device *spi)
{
	struct gpio_desc	*cs;
	int			status = 0;
	struct spi_gpio		*spi_gpio = spi_to_spi_gpio(spi);

	/*
	 * The CS GPIOs have already been
	 * initialized from the descriptor lookup.
	 */
	if (spi_gpio->cs_gpios) {
		cs = spi_gpio->cs_gpios[spi_get_chipselect(spi, 0)];
		if (!spi->controller_state && cs)
			status = gpiod_direction_output(cs,
						  !(spi->mode & SPI_CS_HIGH));
	}

	if (!status)
		status = spi_bitbang_setup(spi);

	return status;
}

static int spi_gpio_set_direction(struct spi_device *spi, bool output)
{
	struct spi_gpio *spi_gpio = spi_to_spi_gpio(spi);
	int ret;

	if (output)
		return gpiod_direction_output(spi_gpio->mosi, 1);

	/*
	 * Only change MOSI to an input if using 3WIRE mode.
	 * Otherwise, MOSI could be left floating if there is
	 * no pull resistor connected to the I/O pin, or could
	 * be left logic high if there is a pull-up. Transmitting
	 * logic high when only clocking MISO data in can put some
	 * SPI devices in to a bad state.
	 */
	if (spi->mode & SPI_3WIRE) {
		ret = gpiod_direction_input(spi_gpio->mosi);
		if (ret)
			return ret;
	}
	/*
	 * Send a turnaround high impedance cycle when switching
	 * from output to input. Theoretically there should be
	 * a clock delay here, but as has been noted above, the
	 * nsec delay function for bit-banged GPIO is simply
	 * {} because bit-banging just doesn't get fast enough
	 * anyway.
	 */
	if (spi->mode & SPI_3WIRE_HIZ) {
		gpiod_set_value_cansleep(spi_gpio->sck,
					 !(spi->mode & SPI_CPOL));
		gpiod_set_value_cansleep(spi_gpio->sck,
					 !!(spi->mode & SPI_CPOL));
	}
	return 0;
}

static void spi_gpio_cleanup(struct spi_device *spi)
{
	spi_bitbang_cleanup(spi);
}

/*
 * It can be convenient to use this driver with pins that have alternate
 * functions associated with a "native" SPI controller if a driver for that
 * controller is not available, or is missing important functionality.
 *
 * On platforms which can do so, configure MISO with a weak pullup unless
 * there's an external pullup on that signal.  That saves power by avoiding
 * floating signals.  (A weak pulldown would save power too, but many
 * drivers expect to see all-ones data as the no target "response".)
 */
static int spi_gpio_request(struct device *dev, struct spi_gpio *spi_gpio)
{
	spi_gpio->mosi = devm_gpiod_get_optional(dev, "mosi", GPIOD_OUT_LOW);
	if (IS_ERR(spi_gpio->mosi))
		return PTR_ERR(spi_gpio->mosi);

	spi_gpio->miso = devm_gpiod_get_optional(dev, "miso", GPIOD_IN);
	if (IS_ERR(spi_gpio->miso))
		return PTR_ERR(spi_gpio->miso);

	spi_gpio->sck = devm_gpiod_get(dev, "sck", GPIOD_OUT_LOW);
	return PTR_ERR_OR_ZERO(spi_gpio->sck);
}

#ifdef CONFIG_OF
static const struct of_device_id spi_gpio_dt_ids[] = {
	{ .compatible = "spi-gpio" },
	{}
};
MODULE_DEVICE_TABLE(of, spi_gpio_dt_ids);

static int spi_gpio_probe_dt(struct platform_device *pdev,
			     struct spi_controller *host)
{
	host->dev.of_node = pdev->dev.of_node;
	host->use_gpio_descriptors = true;

	return 0;
}
#else
static inline int spi_gpio_probe_dt(struct platform_device *pdev,
				    struct spi_controller *host)
{
	return 0;
}
#endif

static int spi_gpio_probe_pdata(struct platform_device *pdev,
				struct spi_controller *host)
{
	struct device *dev = &pdev->dev;
	struct spi_gpio_platform_data *pdata = dev_get_platdata(dev);
	struct spi_gpio *spi_gpio = spi_controller_get_devdata(host);
	int i;

#ifdef GENERIC_BITBANG
	if (!pdata || !pdata->num_chipselect)
		return -ENODEV;
#endif
	/*
	 * The host needs to think there is a chipselect even if not
	 * connected
	 */
	host->num_chipselect = pdata->num_chipselect ?: 1;

	spi_gpio->cs_gpios = devm_kcalloc(dev, host->num_chipselect,
					  sizeof(*spi_gpio->cs_gpios),
					  GFP_KERNEL);
	if (!spi_gpio->cs_gpios)
		return -ENOMEM;

	for (i = 0; i < host->num_chipselect; i++) {
		spi_gpio->cs_gpios[i] = devm_gpiod_get_index(dev, "cs", i,
							     GPIOD_OUT_HIGH);
		if (IS_ERR(spi_gpio->cs_gpios[i]))
			return PTR_ERR(spi_gpio->cs_gpios[i]);
	}

	return 0;
}

static int spi_gpio_probe(struct platform_device *pdev)
{
	int				status;
	struct spi_controller		*host;
	struct spi_gpio			*spi_gpio;
	struct device			*dev = &pdev->dev;
	struct spi_bitbang		*bb;

	host = devm_spi_alloc_host(dev, sizeof(*spi_gpio));
	if (!host)
		return -ENOMEM;

	if (pdev->dev.of_node)
		status = spi_gpio_probe_dt(pdev, host);
	else
		status = spi_gpio_probe_pdata(pdev, host);

	if (status)
		return status;

	spi_gpio = spi_controller_get_devdata(host);

	status = spi_gpio_request(dev, spi_gpio);
	if (status)
		return status;

	host->bits_per_word_mask = SPI_BPW_RANGE_MASK(1, 32);
	host->mode_bits = SPI_3WIRE | SPI_3WIRE_HIZ | SPI_CPHA | SPI_CPOL |
			    SPI_CS_HIGH | SPI_LSB_FIRST;
	if (!spi_gpio->mosi) {
		/* HW configuration without MOSI pin
		 *
		 * No setting SPI_CONTROLLER_NO_RX here - if there is only
		 * a MOSI pin connected the host can still do RX by
		 * changing the direction of the line.
		 */
		host->flags = SPI_CONTROLLER_NO_TX;
	}

	host->bus_num = pdev->id;
	host->setup = spi_gpio_setup;
	host->cleanup = spi_gpio_cleanup;

	bb = &spi_gpio->bitbang;
	bb->master = host;
	/*
	 * There is some additional business, apart from driving the CS GPIO
	 * line, that we need to do on selection. This makes the local
	 * callback for chipselect always get called.
	 */
	host->flags |= SPI_CONTROLLER_GPIO_SS;
	bb->chipselect = spi_gpio_chipselect;
	bb->set_line_direction = spi_gpio_set_direction;

	if (host->flags & SPI_CONTROLLER_NO_TX) {
		bb->txrx_word[SPI_MODE_0] = spi_gpio_spec_txrx_word_mode0;
		bb->txrx_word[SPI_MODE_1] = spi_gpio_spec_txrx_word_mode1;
		bb->txrx_word[SPI_MODE_2] = spi_gpio_spec_txrx_word_mode2;
		bb->txrx_word[SPI_MODE_3] = spi_gpio_spec_txrx_word_mode3;
	} else {
		bb->txrx_word[SPI_MODE_0] = spi_gpio_txrx_word_mode0;
		bb->txrx_word[SPI_MODE_1] = spi_gpio_txrx_word_mode1;
		bb->txrx_word[SPI_MODE_2] = spi_gpio_txrx_word_mode2;
		bb->txrx_word[SPI_MODE_3] = spi_gpio_txrx_word_mode3;
	}
	bb->setup_transfer = spi_bitbang_setup_transfer;

	status = spi_bitbang_init(&spi_gpio->bitbang);
	if (status)
		return status;

	return devm_spi_register_controller(&pdev->dev, host);
}

MODULE_ALIAS("platform:" DRIVER_NAME);

static struct platform_driver spi_gpio_driver = {
	.driver = {
		.name	= DRIVER_NAME,
		.of_match_table = of_match_ptr(spi_gpio_dt_ids),
	},
	.probe		= spi_gpio_probe,
};
module_platform_driver(spi_gpio_driver);

MODULE_DESCRIPTION("SPI host driver using generic bitbanged GPIO ");
MODULE_AUTHOR("David Brownell");
MODULE_LICENSE("GPL");