1// SPDX-License-Identifier: GPL-2.0-or-later
2/*
3 * polling/bitbanging SPI master controller driver utilities
4 */
5
6#include <linux/spinlock.h>
7#include <linux/workqueue.h>
8#include <linux/interrupt.h>
9#include <linux/module.h>
10#include <linux/delay.h>
11#include <linux/errno.h>
12#include <linux/platform_device.h>
13#include <linux/slab.h>
14
15#include <linux/spi/spi.h>
16#include <linux/spi/spi_bitbang.h>
17
18#define SPI_BITBANG_CS_DELAY	100
19
20
21/*----------------------------------------------------------------------*/
22
23/*
24 * FIRST PART (OPTIONAL):  word-at-a-time spi_transfer support.
25 * Use this for GPIO or shift-register level hardware APIs.
26 *
27 * spi_bitbang_cs is in spi_device->controller_state, which is unavailable
28 * to glue code.  These bitbang setup() and cleanup() routines are always
29 * used, though maybe they're called from controller-aware code.
30 *
31 * chipselect() and friends may use spi_device->controller_data and
32 * controller registers as appropriate.
33 *
34 *
35 * NOTE:  SPI controller pins can often be used as GPIO pins instead,
36 * which means you could use a bitbang driver either to get hardware
37 * working quickly, or testing for differences that aren't speed related.
38 */
39
40struct spi_bitbang_cs {
41	unsigned	nsecs;	/* (clock cycle time)/2 */
42	u32		(*txrx_word)(struct spi_device *spi, unsigned nsecs,
43					u32 word, u8 bits, unsigned flags);
44	unsigned	(*txrx_bufs)(struct spi_device *,
45					u32 (*txrx_word)(
46						struct spi_device *spi,
47						unsigned nsecs,
48						u32 word, u8 bits,
49						unsigned flags),
50					unsigned, struct spi_transfer *,
51					unsigned);
52};
53
54static unsigned bitbang_txrx_8(
55	struct spi_device	*spi,
56	u32			(*txrx_word)(struct spi_device *spi,
57					unsigned nsecs,
58					u32 word, u8 bits,
59					unsigned flags),
60	unsigned		ns,
61	struct spi_transfer	*t,
62	unsigned flags
63) {
64	unsigned		bits = t->bits_per_word;
65	unsigned		count = t->len;
66	const u8		*tx = t->tx_buf;
67	u8			*rx = t->rx_buf;
68
69	while (likely(count > 0)) {
70		u8		word = 0;
71
72		if (tx)
73			word = *tx++;
74		word = txrx_word(spi, ns, word, bits, flags);
75		if (rx)
76			*rx++ = word;
77		count -= 1;
78	}
79	return t->len - count;
80}
81
82static unsigned bitbang_txrx_16(
83	struct spi_device	*spi,
84	u32			(*txrx_word)(struct spi_device *spi,
85					unsigned nsecs,
86					u32 word, u8 bits,
87					unsigned flags),
88	unsigned		ns,
89	struct spi_transfer	*t,
90	unsigned flags
91) {
92	unsigned		bits = t->bits_per_word;
93	unsigned		count = t->len;
94	const u16		*tx = t->tx_buf;
95	u16			*rx = t->rx_buf;
96
97	while (likely(count > 1)) {
98		u16		word = 0;
99
100		if (tx)
101			word = *tx++;
102		word = txrx_word(spi, ns, word, bits, flags);
103		if (rx)
104			*rx++ = word;
105		count -= 2;
106	}
107	return t->len - count;
108}
109
110static unsigned bitbang_txrx_32(
111	struct spi_device	*spi,
112	u32			(*txrx_word)(struct spi_device *spi,
113					unsigned nsecs,
114					u32 word, u8 bits,
115					unsigned flags),
116	unsigned		ns,
117	struct spi_transfer	*t,
118	unsigned flags
119) {
120	unsigned		bits = t->bits_per_word;
121	unsigned		count = t->len;
122	const u32		*tx = t->tx_buf;
123	u32			*rx = t->rx_buf;
124
125	while (likely(count > 3)) {
126		u32		word = 0;
127
128		if (tx)
129			word = *tx++;
130		word = txrx_word(spi, ns, word, bits, flags);
131		if (rx)
132			*rx++ = word;
133		count -= 4;
134	}
135	return t->len - count;
136}
137
138int spi_bitbang_setup_transfer(struct spi_device *spi, struct spi_transfer *t)
139{
140	struct spi_bitbang_cs	*cs = spi->controller_state;
141	u8			bits_per_word;
142	u32			hz;
143
144	if (t) {
145		bits_per_word = t->bits_per_word;
146		hz = t->speed_hz;
147	} else {
148		bits_per_word = 0;
149		hz = 0;
150	}
151
152	/* spi_transfer level calls that work per-word */
153	if (!bits_per_word)
154		bits_per_word = spi->bits_per_word;
155	if (bits_per_word <= 8)
156		cs->txrx_bufs = bitbang_txrx_8;
157	else if (bits_per_word <= 16)
158		cs->txrx_bufs = bitbang_txrx_16;
159	else if (bits_per_word <= 32)
160		cs->txrx_bufs = bitbang_txrx_32;
161	else
162		return -EINVAL;
163
164	/* nsecs = (clock period)/2 */
165	if (!hz)
166		hz = spi->max_speed_hz;
167	if (hz) {
168		cs->nsecs = (1000000000/2) / hz;
169		if (cs->nsecs > (MAX_UDELAY_MS * 1000 * 1000))
170			return -EINVAL;
171	}
172
173	return 0;
174}
175EXPORT_SYMBOL_GPL(spi_bitbang_setup_transfer);
176
177/*
178 * spi_bitbang_setup - default setup for per-word I/O loops
179 */
180int spi_bitbang_setup(struct spi_device *spi)
181{
182	struct spi_bitbang_cs	*cs = spi->controller_state;
183	struct spi_bitbang	*bitbang;
184	bool			initial_setup = false;
185	int			retval;
186
187	bitbang = spi_master_get_devdata(spi->master);
188
189	if (!cs) {
190		cs = kzalloc(sizeof(*cs), GFP_KERNEL);
191		if (!cs)
192			return -ENOMEM;
193		spi->controller_state = cs;
194		initial_setup = true;
195	}
196
197	/* per-word shift register access, in hardware or bitbanging */
198	cs->txrx_word = bitbang->txrx_word[spi->mode & (SPI_CPOL|SPI_CPHA)];
199	if (!cs->txrx_word) {
200		retval = -EINVAL;
201		goto err_free;
202	}
203
204	if (bitbang->setup_transfer) {
205		retval = bitbang->setup_transfer(spi, NULL);
206		if (retval < 0)
207			goto err_free;
208	}
209
210	dev_dbg(&spi->dev, "%s, %u nsec/bit\n", __func__, 2 * cs->nsecs);
211
212	return 0;
213
214err_free:
215	if (initial_setup)
216		kfree(cs);
217	return retval;
218}
219EXPORT_SYMBOL_GPL(spi_bitbang_setup);
220
221/*
222 * spi_bitbang_cleanup - default cleanup for per-word I/O loops
223 */
224void spi_bitbang_cleanup(struct spi_device *spi)
225{
226	kfree(spi->controller_state);
227}
228EXPORT_SYMBOL_GPL(spi_bitbang_cleanup);
229
230static int spi_bitbang_bufs(struct spi_device *spi, struct spi_transfer *t)
231{
232	struct spi_bitbang_cs	*cs = spi->controller_state;
233	unsigned		nsecs = cs->nsecs;
234	struct spi_bitbang	*bitbang;
235
236	bitbang = spi_master_get_devdata(spi->master);
237	if (bitbang->set_line_direction) {
238		int err;
239
240		err = bitbang->set_line_direction(spi, !!(t->tx_buf));
241		if (err < 0)
242			return err;
243	}
244
245	if (spi->mode & SPI_3WIRE) {
246		unsigned flags;
247
248		flags = t->tx_buf ? SPI_MASTER_NO_RX : SPI_MASTER_NO_TX;
249		return cs->txrx_bufs(spi, cs->txrx_word, nsecs, t, flags);
250	}
251	return cs->txrx_bufs(spi, cs->txrx_word, nsecs, t, 0);
252}
253
254/*----------------------------------------------------------------------*/
255
256/*
257 * SECOND PART ... simple transfer queue runner.
258 *
259 * This costs a task context per controller, running the queue by
260 * performing each transfer in sequence.  Smarter hardware can queue
261 * several DMA transfers at once, and process several controller queues
262 * in parallel; this driver doesn't match such hardware very well.
263 *
264 * Drivers can provide word-at-a-time i/o primitives, or provide
265 * transfer-at-a-time ones to leverage dma or fifo hardware.
266 */
267
268static int spi_bitbang_prepare_hardware(struct spi_master *spi)
269{
270	struct spi_bitbang	*bitbang;
271
272	bitbang = spi_master_get_devdata(spi);
273
274	mutex_lock(&bitbang->lock);
275	bitbang->busy = 1;
276	mutex_unlock(&bitbang->lock);
277
278	return 0;
279}
280
281static int spi_bitbang_transfer_one(struct spi_master *master,
282				    struct spi_device *spi,
283				    struct spi_transfer *transfer)
284{
285	struct spi_bitbang *bitbang = spi_master_get_devdata(master);
286	int status = 0;
287
288	if (bitbang->setup_transfer) {
289		status = bitbang->setup_transfer(spi, transfer);
290		if (status < 0)
291			goto out;
292	}
293
294	if (transfer->len)
295		status = bitbang->txrx_bufs(spi, transfer);
296
297	if (status == transfer->len)
298		status = 0;
299	else if (status >= 0)
300		status = -EREMOTEIO;
301
302out:
303	spi_finalize_current_transfer(master);
304
305	return status;
306}
307
308static int spi_bitbang_unprepare_hardware(struct spi_master *spi)
309{
310	struct spi_bitbang	*bitbang;
311
312	bitbang = spi_master_get_devdata(spi);
313
314	mutex_lock(&bitbang->lock);
315	bitbang->busy = 0;
316	mutex_unlock(&bitbang->lock);
317
318	return 0;
319}
320
321static void spi_bitbang_set_cs(struct spi_device *spi, bool enable)
322{
323	struct spi_bitbang *bitbang = spi_master_get_devdata(spi->master);
324
325	/* SPI core provides CS high / low, but bitbang driver
326	 * expects CS active
327	 * spi device driver takes care of handling SPI_CS_HIGH
328	 */
329	enable = (!!(spi->mode & SPI_CS_HIGH) == enable);
330
331	ndelay(SPI_BITBANG_CS_DELAY);
332	bitbang->chipselect(spi, enable ? BITBANG_CS_ACTIVE :
333			    BITBANG_CS_INACTIVE);
334	ndelay(SPI_BITBANG_CS_DELAY);
335}
336
337/*----------------------------------------------------------------------*/
338
339int spi_bitbang_init(struct spi_bitbang *bitbang)
340{
341	struct spi_master *master = bitbang->master;
342	bool custom_cs;
343
344	if (!master)
345		return -EINVAL;
346	/*
347	 * We only need the chipselect callback if we are actually using it.
348	 * If we just use GPIO descriptors, it is surplus. If the
349	 * SPI_MASTER_GPIO_SS flag is set, we always need to call the
350	 * driver-specific chipselect routine.
351	 */
352	custom_cs = (!master->use_gpio_descriptors ||
353		     (master->flags & SPI_MASTER_GPIO_SS));
354
355	if (custom_cs && !bitbang->chipselect)
356		return -EINVAL;
357
358	mutex_init(&bitbang->lock);
359
360	if (!master->mode_bits)
361		master->mode_bits = SPI_CPOL | SPI_CPHA | bitbang->flags;
362
363	if (master->transfer || master->transfer_one_message)
364		return -EINVAL;
365
366	master->prepare_transfer_hardware = spi_bitbang_prepare_hardware;
367	master->unprepare_transfer_hardware = spi_bitbang_unprepare_hardware;
368	master->transfer_one = spi_bitbang_transfer_one;
369	/*
370	 * When using GPIO descriptors, the ->set_cs() callback doesn't even
371	 * get called unless SPI_MASTER_GPIO_SS is set.
372	 */
373	if (custom_cs)
374		master->set_cs = spi_bitbang_set_cs;
375
376	if (!bitbang->txrx_bufs) {
377		bitbang->use_dma = 0;
378		bitbang->txrx_bufs = spi_bitbang_bufs;
379		if (!master->setup) {
380			if (!bitbang->setup_transfer)
381				bitbang->setup_transfer =
382					 spi_bitbang_setup_transfer;
383			master->setup = spi_bitbang_setup;
384			master->cleanup = spi_bitbang_cleanup;
385		}
386	}
387
388	return 0;
389}
390EXPORT_SYMBOL_GPL(spi_bitbang_init);
391
392/**
393 * spi_bitbang_start - start up a polled/bitbanging SPI master driver
394 * @bitbang: driver handle
395 *
396 * Caller should have zero-initialized all parts of the structure, and then
397 * provided callbacks for chip selection and I/O loops.  If the master has
398 * a transfer method, its final step should call spi_bitbang_transfer; or,
399 * that's the default if the transfer routine is not initialized.  It should
400 * also set up the bus number and number of chipselects.
401 *
402 * For i/o loops, provide callbacks either per-word (for bitbanging, or for
403 * hardware that basically exposes a shift register) or per-spi_transfer
404 * (which takes better advantage of hardware like fifos or DMA engines).
405 *
406 * Drivers using per-word I/O loops should use (or call) spi_bitbang_setup,
407 * spi_bitbang_cleanup and spi_bitbang_setup_transfer to handle those spi
408 * master methods.  Those methods are the defaults if the bitbang->txrx_bufs
409 * routine isn't initialized.
410 *
411 * This routine registers the spi_master, which will process requests in a
412 * dedicated task, keeping IRQs unblocked most of the time.  To stop
413 * processing those requests, call spi_bitbang_stop().
414 *
415 * On success, this routine will take a reference to master. The caller is
416 * responsible for calling spi_bitbang_stop() to decrement the reference and
417 * spi_master_put() as counterpart of spi_alloc_master() to prevent a memory
418 * leak.
419 */
420int spi_bitbang_start(struct spi_bitbang *bitbang)
421{
422	struct spi_master *master = bitbang->master;
423	int ret;
424
425	ret = spi_bitbang_init(bitbang);
426	if (ret)
427		return ret;
428
429	/* driver may get busy before register() returns, especially
430	 * if someone registered boardinfo for devices
431	 */
432	ret = spi_register_master(spi_master_get(master));
433	if (ret)
434		spi_master_put(master);
435
436	return ret;
437}
438EXPORT_SYMBOL_GPL(spi_bitbang_start);
439
440/*
441 * spi_bitbang_stop - stops the task providing spi communication
442 */
443void spi_bitbang_stop(struct spi_bitbang *bitbang)
444{
445	spi_unregister_master(bitbang->master);
446}
447EXPORT_SYMBOL_GPL(spi_bitbang_stop);
448
449MODULE_LICENSE("GPL");
450
451