1// SPDX-License-Identifier: GPL-2.0-or-later
2/*
3 * SPI master driver for ICP DAS LP-8841 RTC
4 *
5 * Copyright (C) 2016 Sergei Ianovich
6 *
7 * based on
8 *
9 * Dallas DS1302 RTC Support
10 * Copyright (C) 2002 David McCullough
11 * Copyright (C) 2003 - 2007 Paul Mundt
12 */
13#include <linux/delay.h>
14#include <linux/kernel.h>
15#include <linux/module.h>
16#include <linux/platform_device.h>
17#include <linux/of.h>
18#include <linux/of_device.h>
19#include <linux/spi/spi.h>
20
21#define DRIVER_NAME	"spi_lp8841_rtc"
22
23#define SPI_LP8841_RTC_CE	0x01
24#define SPI_LP8841_RTC_CLK	0x02
25#define SPI_LP8841_RTC_nWE	0x04
26#define SPI_LP8841_RTC_MOSI	0x08
27#define SPI_LP8841_RTC_MISO	0x01
28
29/*
30 * REVISIT If there is support for SPI_3WIRE and SPI_LSB_FIRST in SPI
31 * GPIO driver, this SPI driver can be replaced by a simple GPIO driver
32 * providing 3 GPIO pins.
33 */
34
35struct spi_lp8841_rtc {
36	void		*iomem;
37	unsigned long	state;
38};
39
40static inline void
41setsck(struct spi_lp8841_rtc *data, int is_on)
42{
43	if (is_on)
44		data->state |= SPI_LP8841_RTC_CLK;
45	else
46		data->state &= ~SPI_LP8841_RTC_CLK;
47	writeb(data->state, data->iomem);
48}
49
50static inline void
51setmosi(struct spi_lp8841_rtc *data, int is_on)
52{
53	if (is_on)
54		data->state |= SPI_LP8841_RTC_MOSI;
55	else
56		data->state &= ~SPI_LP8841_RTC_MOSI;
57	writeb(data->state, data->iomem);
58}
59
60static inline int
61getmiso(struct spi_lp8841_rtc *data)
62{
63	return ioread8(data->iomem) & SPI_LP8841_RTC_MISO;
64}
65
66static inline u32
67bitbang_txrx_be_cpha0_lsb(struct spi_lp8841_rtc *data,
68		unsigned usecs, unsigned cpol, unsigned flags,
69		u32 word, u8 bits)
70{
71	/* if (cpol == 0) this is SPI_MODE_0; else this is SPI_MODE_2 */
72
73	u32 shift = 32 - bits;
74	/* clock starts at inactive polarity */
75	for (; likely(bits); bits--) {
76
77		/* setup LSB (to slave) on leading edge */
78		if ((flags & SPI_MASTER_NO_TX) == 0)
79			setmosi(data, (word & 1));
80
81		usleep_range(usecs, usecs + 1);	/* T(setup) */
82
83		/* sample LSB (from slave) on trailing edge */
84		word >>= 1;
85		if ((flags & SPI_MASTER_NO_RX) == 0)
86			word |= (getmiso(data) << 31);
87
88		setsck(data, !cpol);
89		usleep_range(usecs, usecs + 1);
90
91		setsck(data, cpol);
92	}
93
94	word >>= shift;
95	return word;
96}
97
98static int
99spi_lp8841_rtc_transfer_one(struct spi_master *master,
100			    struct spi_device *spi,
101			    struct spi_transfer *t)
102{
103	struct spi_lp8841_rtc	*data = spi_master_get_devdata(master);
104	unsigned		count = t->len;
105	const u8		*tx = t->tx_buf;
106	u8			*rx = t->rx_buf;
107	u8			word = 0;
108	int			ret = 0;
109
110	if (tx) {
111		data->state &= ~SPI_LP8841_RTC_nWE;
112		writeb(data->state, data->iomem);
113		while (likely(count > 0)) {
114			word = *tx++;
115			bitbang_txrx_be_cpha0_lsb(data, 1, 0,
116					SPI_MASTER_NO_RX, word, 8);
117			count--;
118		}
119	} else if (rx) {
120		data->state |= SPI_LP8841_RTC_nWE;
121		writeb(data->state, data->iomem);
122		while (likely(count > 0)) {
123			word = bitbang_txrx_be_cpha0_lsb(data, 1, 0,
124					SPI_MASTER_NO_TX, word, 8);
125			*rx++ = word;
126			count--;
127		}
128	} else {
129		ret = -EINVAL;
130	}
131
132	spi_finalize_current_transfer(master);
133
134	return ret;
135}
136
137static void
138spi_lp8841_rtc_set_cs(struct spi_device *spi, bool enable)
139{
140	struct spi_lp8841_rtc *data = spi_master_get_devdata(spi->master);
141
142	data->state = 0;
143	writeb(data->state, data->iomem);
144	if (enable) {
145		usleep_range(4, 5);
146		data->state |= SPI_LP8841_RTC_CE;
147		writeb(data->state, data->iomem);
148		usleep_range(4, 5);
149	}
150}
151
152static int
153spi_lp8841_rtc_setup(struct spi_device *spi)
154{
155	if ((spi->mode & SPI_CS_HIGH) == 0) {
156		dev_err(&spi->dev, "unsupported active low chip select\n");
157		return -EINVAL;
158	}
159
160	if ((spi->mode & SPI_LSB_FIRST) == 0) {
161		dev_err(&spi->dev, "unsupported MSB first mode\n");
162		return -EINVAL;
163	}
164
165	if ((spi->mode & SPI_3WIRE) == 0) {
166		dev_err(&spi->dev, "unsupported wiring. 3 wires required\n");
167		return -EINVAL;
168	}
169
170	return 0;
171}
172
173#ifdef CONFIG_OF
174static const struct of_device_id spi_lp8841_rtc_dt_ids[] = {
175	{ .compatible = "icpdas,lp8841-spi-rtc" },
176	{ }
177};
178
179MODULE_DEVICE_TABLE(of, spi_lp8841_rtc_dt_ids);
180#endif
181
182static int
183spi_lp8841_rtc_probe(struct platform_device *pdev)
184{
185	int				ret;
186	struct spi_master		*master;
187	struct spi_lp8841_rtc		*data;
188
189	master = spi_alloc_master(&pdev->dev, sizeof(*data));
190	if (!master)
191		return -ENOMEM;
192	platform_set_drvdata(pdev, master);
193
194	master->flags = SPI_MASTER_HALF_DUPLEX;
195	master->mode_bits = SPI_CS_HIGH | SPI_3WIRE | SPI_LSB_FIRST;
196
197	master->bus_num = pdev->id;
198	master->num_chipselect = 1;
199	master->setup = spi_lp8841_rtc_setup;
200	master->set_cs = spi_lp8841_rtc_set_cs;
201	master->transfer_one = spi_lp8841_rtc_transfer_one;
202	master->bits_per_word_mask = SPI_BPW_MASK(8);
203#ifdef CONFIG_OF
204	master->dev.of_node = pdev->dev.of_node;
205#endif
206
207	data = spi_master_get_devdata(master);
208
209	data->iomem = devm_platform_ioremap_resource(pdev, 0);
210	ret = PTR_ERR_OR_ZERO(data->iomem);
211	if (ret) {
212		dev_err(&pdev->dev, "failed to get IO address\n");
213		goto err_put_master;
214	}
215
216	/* register with the SPI framework */
217	ret = devm_spi_register_master(&pdev->dev, master);
218	if (ret) {
219		dev_err(&pdev->dev, "cannot register spi master\n");
220		goto err_put_master;
221	}
222
223	return ret;
224
225
226err_put_master:
227	spi_master_put(master);
228
229	return ret;
230}
231
232MODULE_ALIAS("platform:" DRIVER_NAME);
233
234static struct platform_driver spi_lp8841_rtc_driver = {
235	.driver = {
236		.name	= DRIVER_NAME,
237		.of_match_table = of_match_ptr(spi_lp8841_rtc_dt_ids),
238	},
239	.probe		= spi_lp8841_rtc_probe,
240};
241module_platform_driver(spi_lp8841_rtc_driver);
242
243MODULE_DESCRIPTION("SPI master driver for ICP DAS LP-8841 RTC");
244MODULE_AUTHOR("Sergei Ianovich");
245MODULE_LICENSE("GPL");
246