1/*
  2 * SPI master driver for ICP DAS LP-8841 RTC
  3 *
  4 * Copyright (C) 2016 Sergei Ianovich
  5 *
  6 * based on
  7 *
  8 * Dallas DS1302 RTC Support
  9 * Copyright (C) 2002 David McCullough
 10 * Copyright (C) 2003 - 2007 Paul Mundt
 11 *
 12 * This program is free software; you can redistribute it and/or modify
 13 * it under the terms of the GNU General Public License as published by
 14 * the Free Software Foundation; either version 2 of the License, or
 15 * (at your option) any later version.
 16 *
 17 * This program is distributed in the hope that it will be useful,
 18 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 19 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 20 * GNU General Public License for more details.
 21 */
 22#include <linux/delay.h>
 23#include <linux/kernel.h>
 24#include <linux/module.h>
 25#include <linux/platform_device.h>
 26#include <linux/of.h>
 27#include <linux/of_device.h>
 28#include <linux/spi/spi.h>
 29
 30#define DRIVER_NAME	"spi_lp8841_rtc"
 31
 32#define SPI_LP8841_RTC_CE	0x01
 33#define SPI_LP8841_RTC_CLK	0x02
 34#define SPI_LP8841_RTC_nWE	0x04
 35#define SPI_LP8841_RTC_MOSI	0x08
 36#define SPI_LP8841_RTC_MISO	0x01
 37
 38/*
 39 * REVISIT If there is support for SPI_3WIRE and SPI_LSB_FIRST in SPI
 40 * GPIO driver, this SPI driver can be replaced by a simple GPIO driver
 41 * providing 3 GPIO pins.
 42 */
 43
 44struct spi_lp8841_rtc {
 45	void		*iomem;
 46	unsigned long	state;
 47};
 48
 49static inline void
 50setsck(struct spi_lp8841_rtc *data, int is_on)
 51{
 52	if (is_on)
 53		data->state |= SPI_LP8841_RTC_CLK;
 54	else
 55		data->state &= ~SPI_LP8841_RTC_CLK;
 56	writeb(data->state, data->iomem);
 57}
 58
 59static inline void
 60setmosi(struct spi_lp8841_rtc *data, int is_on)
 61{
 62	if (is_on)
 63		data->state |= SPI_LP8841_RTC_MOSI;
 64	else
 65		data->state &= ~SPI_LP8841_RTC_MOSI;
 66	writeb(data->state, data->iomem);
 67}
 68
 69static inline int
 70getmiso(struct spi_lp8841_rtc *data)
 71{
 72	return ioread8(data->iomem) & SPI_LP8841_RTC_MISO;
 73}
 74
 75static inline u32
 76bitbang_txrx_be_cpha0_lsb(struct spi_lp8841_rtc *data,
 77		unsigned usecs, unsigned cpol, unsigned flags,
 78		u32 word, u8 bits)
 79{
 80	/* if (cpol == 0) this is SPI_MODE_0; else this is SPI_MODE_2 */
 81
 82	u32 shift = 32 - bits;
 83	/* clock starts at inactive polarity */
 84	for (; likely(bits); bits--) {
 85
 86		/* setup LSB (to slave) on leading edge */
 87		if ((flags & SPI_MASTER_NO_TX) == 0)
 88			setmosi(data, (word & 1));
 89
 90		usleep_range(usecs, usecs + 1);	/* T(setup) */
 91
 92		/* sample LSB (from slave) on trailing edge */
 93		word >>= 1;
 94		if ((flags & SPI_MASTER_NO_RX) == 0)
 95			word |= (getmiso(data) << 31);
 96
 97		setsck(data, !cpol);
 98		usleep_range(usecs, usecs + 1);
 99
100		setsck(data, cpol);
101	}
102
103	word >>= shift;
104	return word;
105}
106
107static int
108spi_lp8841_rtc_transfer_one(struct spi_master *master,
109			    struct spi_device *spi,
110			    struct spi_transfer *t)
111{
112	struct spi_lp8841_rtc	*data = spi_master_get_devdata(master);
113	unsigned		count = t->len;
114	const u8		*tx = t->tx_buf;
115	u8			*rx = t->rx_buf;
116	u8			word = 0;
117	int			ret = 0;
118
119	if (tx) {
120		data->state &= ~SPI_LP8841_RTC_nWE;
121		writeb(data->state, data->iomem);
122		while (likely(count > 0)) {
123			word = *tx++;
124			bitbang_txrx_be_cpha0_lsb(data, 1, 0,
125					SPI_MASTER_NO_RX, word, 8);
126			count--;
127		}
128	} else if (rx) {
129		data->state |= SPI_LP8841_RTC_nWE;
130		writeb(data->state, data->iomem);
131		while (likely(count > 0)) {
132			word = bitbang_txrx_be_cpha0_lsb(data, 1, 0,
133					SPI_MASTER_NO_TX, word, 8);
134			*rx++ = word;
135			count--;
136		}
137	} else {
138		ret = -EINVAL;
139	}
140
141	spi_finalize_current_transfer(master);
142
143	return ret;
144}
145
146static void
147spi_lp8841_rtc_set_cs(struct spi_device *spi, bool enable)
148{
149	struct spi_lp8841_rtc *data = spi_master_get_devdata(spi->master);
150
151	data->state = 0;
152	writeb(data->state, data->iomem);
153	if (enable) {
154		usleep_range(4, 5);
155		data->state |= SPI_LP8841_RTC_CE;
156		writeb(data->state, data->iomem);
157		usleep_range(4, 5);
158	}
159}
160
161static int
162spi_lp8841_rtc_setup(struct spi_device *spi)
163{
164	if ((spi->mode & SPI_CS_HIGH) == 0) {
165		dev_err(&spi->dev, "unsupported active low chip select\n");
166		return -EINVAL;
167	}
168
169	if ((spi->mode & SPI_LSB_FIRST) == 0) {
170		dev_err(&spi->dev, "unsupported MSB first mode\n");
171		return -EINVAL;
172	}
173
174	if ((spi->mode & SPI_3WIRE) == 0) {
175		dev_err(&spi->dev, "unsupported wiring. 3 wires required\n");
176		return -EINVAL;
177	}
178
179	return 0;
180}
181
182#ifdef CONFIG_OF
183static const struct of_device_id spi_lp8841_rtc_dt_ids[] = {
184	{ .compatible = "icpdas,lp8841-spi-rtc" },
185	{ }
186};
187
188MODULE_DEVICE_TABLE(of, spi_lp8841_rtc_dt_ids);
189#endif
190
191static int
192spi_lp8841_rtc_probe(struct platform_device *pdev)
193{
194	int				ret;
195	struct spi_master		*master;
196	struct spi_lp8841_rtc		*data;
197	void				*iomem;
198
199	master = spi_alloc_master(&pdev->dev, sizeof(*data));
200	if (!master)
201		return -ENOMEM;
202	platform_set_drvdata(pdev, master);
203
204	master->flags = SPI_MASTER_HALF_DUPLEX;
205	master->mode_bits = SPI_CS_HIGH | SPI_3WIRE | SPI_LSB_FIRST;
206
207	master->bus_num = pdev->id;
208	master->num_chipselect = 1;
209	master->setup = spi_lp8841_rtc_setup;
210	master->set_cs = spi_lp8841_rtc_set_cs;
211	master->transfer_one = spi_lp8841_rtc_transfer_one;
212	master->bits_per_word_mask = SPI_BPW_MASK(8);
213#ifdef CONFIG_OF
214	master->dev.of_node = pdev->dev.of_node;
215#endif
216
217	data = spi_master_get_devdata(master);
218
219	iomem = platform_get_resource(pdev, IORESOURCE_MEM, 0);
220	data->iomem = devm_ioremap_resource(&pdev->dev, iomem);
221	ret = PTR_ERR_OR_ZERO(data->iomem);
222	if (ret) {
223		dev_err(&pdev->dev, "failed to get IO address\n");
224		goto err_put_master;
225	}
226
227	/* register with the SPI framework */
228	ret = devm_spi_register_master(&pdev->dev, master);
229	if (ret) {
230		dev_err(&pdev->dev, "cannot register spi master\n");
231		goto err_put_master;
232	}
233
234	return ret;
235
236
237err_put_master:
238	spi_master_put(master);
239
240	return ret;
241}
242
243MODULE_ALIAS("platform:" DRIVER_NAME);
244
245static struct platform_driver spi_lp8841_rtc_driver = {
246	.driver = {
247		.name	= DRIVER_NAME,
248		.of_match_table = of_match_ptr(spi_lp8841_rtc_dt_ids),
249	},
250	.probe		= spi_lp8841_rtc_probe,
251};
252module_platform_driver(spi_lp8841_rtc_driver);
253
254MODULE_DESCRIPTION("SPI master driver for ICP DAS LP-8841 RTC");
255MODULE_AUTHOR("Sergei Ianovich");
256MODULE_LICENSE("GPL");