1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * NBUS driver for TS-4600 based boards
4 *
5 * Copyright (c) 2016 - Savoir-faire Linux
6 * Author: Sebastien Bourdelin <sebastien.bourdelin@savoirfairelinux.com>
7 *
8 * This driver implements a GPIOs bit-banged bus, called the NBUS by Technologic
9 * Systems. It is used to communicate with the peripherals in the FPGA on the
10 * TS-4600 SoM.
11 */
12
13#include <linux/bitops.h>
14#include <linux/gpio/consumer.h>
15#include <linux/kernel.h>
16#include <linux/module.h>
17#include <linux/mutex.h>
18#include <linux/of_platform.h>
19#include <linux/platform_device.h>
20#include <linux/pwm.h>
21#include <linux/ts-nbus.h>
22
23#define TS_NBUS_DIRECTION_IN  0
24#define TS_NBUS_DIRECTION_OUT 1
25#define TS_NBUS_WRITE_ADR 0
26#define TS_NBUS_WRITE_VAL 1
27
28struct ts_nbus {
29	struct pwm_device *pwm;
30	struct gpio_descs *data;
31	struct gpio_desc *csn;
32	struct gpio_desc *txrx;
33	struct gpio_desc *strobe;
34	struct gpio_desc *ale;
35	struct gpio_desc *rdy;
36	struct mutex lock;
37};
38
39/*
40 * request all gpios required by the bus.
41 */
42static int ts_nbus_init_pdata(struct platform_device *pdev,
43			      struct ts_nbus *ts_nbus)
44{
45	ts_nbus->data = devm_gpiod_get_array(&pdev->dev, "ts,data",
46			GPIOD_OUT_HIGH);
47	if (IS_ERR(ts_nbus->data))
48		return dev_err_probe(&pdev->dev, PTR_ERR(ts_nbus->data),
49				     "failed to retrieve ts,data-gpio from dts\n");
50
51	ts_nbus->csn = devm_gpiod_get(&pdev->dev, "ts,csn", GPIOD_OUT_HIGH);
52	if (IS_ERR(ts_nbus->csn))
53		return dev_err_probe(&pdev->dev, PTR_ERR(ts_nbus->csn),
54			      "failed to retrieve ts,csn-gpio from dts\n");
55
56	ts_nbus->txrx = devm_gpiod_get(&pdev->dev, "ts,txrx", GPIOD_OUT_HIGH);
57	if (IS_ERR(ts_nbus->txrx))
58		return dev_err_probe(&pdev->dev, PTR_ERR(ts_nbus->txrx),
59				     "failed to retrieve ts,txrx-gpio from dts\n");
60
61	ts_nbus->strobe = devm_gpiod_get(&pdev->dev, "ts,strobe", GPIOD_OUT_HIGH);
62	if (IS_ERR(ts_nbus->strobe))
63		return dev_err_probe(&pdev->dev, PTR_ERR(ts_nbus->strobe),
64				     "failed to retrieve ts,strobe-gpio from dts\n");
65
66	ts_nbus->ale = devm_gpiod_get(&pdev->dev, "ts,ale", GPIOD_OUT_HIGH);
67	if (IS_ERR(ts_nbus->ale))
68		return dev_err_probe(&pdev->dev, PTR_ERR(ts_nbus->ale),
69				     "failed to retrieve ts,ale-gpio from dts\n");
70
71	ts_nbus->rdy = devm_gpiod_get(&pdev->dev, "ts,rdy", GPIOD_IN);
72	if (IS_ERR(ts_nbus->rdy))
73		return dev_err_probe(&pdev->dev, PTR_ERR(ts_nbus->rdy),
74				     "failed to retrieve ts,rdy-gpio from dts\n");
75
76	return 0;
77}
78
79/*
80 * the data gpios are used for reading and writing values, their directions
81 * should be adjusted accordingly.
82 */
83static void ts_nbus_set_direction(struct ts_nbus *ts_nbus, int direction)
84{
85	int i;
86
87	for (i = 0; i < 8; i++) {
88		if (direction == TS_NBUS_DIRECTION_IN)
89			gpiod_direction_input(ts_nbus->data->desc[i]);
90		else
91			/* when used as output the default state of the data
92			 * lines are set to high */
93			gpiod_direction_output(ts_nbus->data->desc[i], 1);
94	}
95}
96
97/*
98 * reset the bus in its initial state.
99 * The data, csn, strobe and ale lines must be zero'ed to let the FPGA knows a
100 * new transaction can be process.
101 */
102static void ts_nbus_reset_bus(struct ts_nbus *ts_nbus)
103{
104	DECLARE_BITMAP(values, 8);
105
106	values[0] = 0;
107
108	gpiod_set_array_value_cansleep(8, ts_nbus->data->desc,
109				       ts_nbus->data->info, values);
110	gpiod_set_value_cansleep(ts_nbus->csn, 0);
111	gpiod_set_value_cansleep(ts_nbus->strobe, 0);
112	gpiod_set_value_cansleep(ts_nbus->ale, 0);
113}
114
115/*
116 * let the FPGA knows it can process.
117 */
118static void ts_nbus_start_transaction(struct ts_nbus *ts_nbus)
119{
120	gpiod_set_value_cansleep(ts_nbus->strobe, 1);
121}
122
123/*
124 * read a byte value from the data gpios.
125 * return 0 on success or negative errno on failure.
126 */
127static int ts_nbus_read_byte(struct ts_nbus *ts_nbus, u8 *val)
128{
129	struct gpio_descs *gpios = ts_nbus->data;
130	int ret, i;
131
132	*val = 0;
133	for (i = 0; i < 8; i++) {
134		ret = gpiod_get_value_cansleep(gpios->desc[i]);
135		if (ret < 0)
136			return ret;
137		if (ret)
138			*val |= BIT(i);
139	}
140
141	return 0;
142}
143
144/*
145 * set the data gpios accordingly to the byte value.
146 */
147static void ts_nbus_write_byte(struct ts_nbus *ts_nbus, u8 byte)
148{
149	struct gpio_descs *gpios = ts_nbus->data;
150	DECLARE_BITMAP(values, 8);
151
152	values[0] = byte;
153
154	gpiod_set_array_value_cansleep(8, gpios->desc, gpios->info, values);
155}
156
157/*
158 * reading the bus consists of resetting the bus, then notifying the FPGA to
159 * send the data in the data gpios and return the read value.
160 * return 0 on success or negative errno on failure.
161 */
162static int ts_nbus_read_bus(struct ts_nbus *ts_nbus, u8 *val)
163{
164	ts_nbus_reset_bus(ts_nbus);
165	ts_nbus_start_transaction(ts_nbus);
166
167	return ts_nbus_read_byte(ts_nbus, val);
168}
169
170/*
171 * writing to the bus consists of resetting the bus, then define the type of
172 * command (address/value), write the data and notify the FPGA to retrieve the
173 * value in the data gpios.
174 */
175static void ts_nbus_write_bus(struct ts_nbus *ts_nbus, int cmd, u8 val)
176{
177	ts_nbus_reset_bus(ts_nbus);
178
179	if (cmd == TS_NBUS_WRITE_ADR)
180		gpiod_set_value_cansleep(ts_nbus->ale, 1);
181
182	ts_nbus_write_byte(ts_nbus, val);
183	ts_nbus_start_transaction(ts_nbus);
184}
185
186/*
187 * read the value in the FPGA register at the given address.
188 * return 0 on success or negative errno on failure.
189 */
190int ts_nbus_read(struct ts_nbus *ts_nbus, u8 adr, u16 *val)
191{
192	int ret, i;
193	u8 byte;
194
195	/* bus access must be atomic */
196	mutex_lock(&ts_nbus->lock);
197
198	/* set the bus in read mode */
199	gpiod_set_value_cansleep(ts_nbus->txrx, 0);
200
201	/* write address */
202	ts_nbus_write_bus(ts_nbus, TS_NBUS_WRITE_ADR, adr);
203
204	/* set the data gpios direction as input before reading */
205	ts_nbus_set_direction(ts_nbus, TS_NBUS_DIRECTION_IN);
206
207	/* reading value MSB first */
208	do {
209		*val = 0;
210		byte = 0;
211		for (i = 1; i >= 0; i--) {
212			/* read a byte from the bus, leave on error */
213			ret = ts_nbus_read_bus(ts_nbus, &byte);
214			if (ret < 0)
215				goto err;
216
217			/* append the byte read to the final value */
218			*val |= byte << (i * 8);
219		}
220		gpiod_set_value_cansleep(ts_nbus->csn, 1);
221		ret = gpiod_get_value_cansleep(ts_nbus->rdy);
222	} while (ret);
223
224err:
225	/* restore the data gpios direction as output after reading */
226	ts_nbus_set_direction(ts_nbus, TS_NBUS_DIRECTION_OUT);
227
228	mutex_unlock(&ts_nbus->lock);
229
230	return ret;
231}
232EXPORT_SYMBOL_GPL(ts_nbus_read);
233
234/*
235 * write the desired value in the FPGA register at the given address.
236 */
237int ts_nbus_write(struct ts_nbus *ts_nbus, u8 adr, u16 val)
238{
239	int i;
240
241	/* bus access must be atomic */
242	mutex_lock(&ts_nbus->lock);
243
244	/* set the bus in write mode */
245	gpiod_set_value_cansleep(ts_nbus->txrx, 1);
246
247	/* write address */
248	ts_nbus_write_bus(ts_nbus, TS_NBUS_WRITE_ADR, adr);
249
250	/* writing value MSB first */
251	for (i = 1; i >= 0; i--)
252		ts_nbus_write_bus(ts_nbus, TS_NBUS_WRITE_VAL, (u8)(val >> (i * 8)));
253
254	/* wait for completion */
255	gpiod_set_value_cansleep(ts_nbus->csn, 1);
256	while (gpiod_get_value_cansleep(ts_nbus->rdy) != 0) {
257		gpiod_set_value_cansleep(ts_nbus->csn, 0);
258		gpiod_set_value_cansleep(ts_nbus->csn, 1);
259	}
260
261	mutex_unlock(&ts_nbus->lock);
262
263	return 0;
264}
265EXPORT_SYMBOL_GPL(ts_nbus_write);
266
267static int ts_nbus_probe(struct platform_device *pdev)
268{
269	struct pwm_device *pwm;
270	struct pwm_state state;
271	struct device *dev = &pdev->dev;
272	struct ts_nbus *ts_nbus;
273	int ret;
274
275	ts_nbus = devm_kzalloc(dev, sizeof(*ts_nbus), GFP_KERNEL);
276	if (!ts_nbus)
277		return -ENOMEM;
278
279	mutex_init(&ts_nbus->lock);
280
281	ret = ts_nbus_init_pdata(pdev, ts_nbus);
282	if (ret < 0)
283		return ret;
284
285	pwm = devm_pwm_get(dev, NULL);
286	if (IS_ERR(pwm))
287		return dev_err_probe(dev, PTR_ERR(pwm),
288				     "unable to request PWM\n");
289
290	pwm_init_state(pwm, &state);
291	if (!state.period)
292		return dev_err_probe(dev, -EINVAL, "invalid PWM period\n");
293
294	state.duty_cycle = state.period;
295	state.enabled = true;
296
297	ret = pwm_apply_state(pwm, &state);
298	if (ret < 0)
299		return dev_err_probe(dev, ret, "failed to configure PWM\n");
300
301	/*
302	 * we can now start the FPGA and populate the peripherals.
303	 */
304	ts_nbus->pwm = pwm;
305
306	/*
307	 * let the child nodes retrieve this instance of the ts-nbus.
308	 */
309	dev_set_drvdata(dev, ts_nbus);
310
311	ret = of_platform_populate(dev->of_node, NULL, NULL, dev);
312	if (ret < 0)
313		return dev_err_probe(dev, ret,
314				     "failed to populate platform devices on bus\n");
315
316	dev_info(dev, "initialized\n");
317
318	return 0;
319}
320
321static void ts_nbus_remove(struct platform_device *pdev)
322{
323	struct ts_nbus *ts_nbus = dev_get_drvdata(&pdev->dev);
324
325	/* shutdown the FPGA */
326	mutex_lock(&ts_nbus->lock);
327	pwm_disable(ts_nbus->pwm);
328	mutex_unlock(&ts_nbus->lock);
329}
330
331static const struct of_device_id ts_nbus_of_match[] = {
332	{ .compatible = "technologic,ts-nbus", },
333	{ },
334};
335MODULE_DEVICE_TABLE(of, ts_nbus_of_match);
336
337static struct platform_driver ts_nbus_driver = {
338	.probe		= ts_nbus_probe,
339	.remove_new	= ts_nbus_remove,
340	.driver		= {
341		.name	= "ts_nbus",
342		.of_match_table = ts_nbus_of_match,
343	},
344};
345
346module_platform_driver(ts_nbus_driver);
347
348MODULE_ALIAS("platform:ts_nbus");
349MODULE_AUTHOR("Sebastien Bourdelin <sebastien.bourdelin@savoirfairelinux.com>");
350MODULE_DESCRIPTION("Technologic Systems NBUS");
351MODULE_LICENSE("GPL v2");
352