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David Brownelld29389d2009-01-06 14:41:41 -08001/*
2 * spi_gpio.c - SPI master driver using generic bitbanged GPIO
3 *
4 * Copyright (C) 2006,2008 David Brownell
5 *
6 * This program is free software; you can redistribute it and/or modify
7 * it under the terms of the GNU General Public License as published by
8 * the Free Software Foundation; either version 2 of the License, or
9 * (at your option) any later version.
10 *
11 * This program is distributed in the hope that it will be useful,
12 * but WITHOUT ANY WARRANTY; without even the implied warranty of
13 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 * GNU General Public License for more details.
15 *
16 * You should have received a copy of the GNU General Public License
17 * along with this program; if not, write to the Free Software
18 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
19 */
20#include <linux/kernel.h>
21#include <linux/init.h>
22#include <linux/platform_device.h>
23#include <linux/gpio.h>
24
25#include <linux/spi/spi.h>
26#include <linux/spi/spi_bitbang.h>
27#include <linux/spi/spi_gpio.h>
28
29
30/*
31 * This bitbanging SPI master driver should help make systems usable
32 * when a native hardware SPI engine is not available, perhaps because
33 * its driver isn't yet working or because the I/O pins it requires
34 * are used for other purposes.
35 *
36 * platform_device->driver_data ... points to spi_gpio
37 *
38 * spi->controller_state ... reserved for bitbang framework code
39 * spi->controller_data ... holds chipselect GPIO
40 *
41 * spi->master->dev.driver_data ... points to spi_gpio->bitbang
42 */
43
44struct spi_gpio {
45 struct spi_bitbang bitbang;
46 struct spi_gpio_platform_data pdata;
47 struct platform_device *pdev;
48};
49
50/*----------------------------------------------------------------------*/
51
52/*
53 * Because the overhead of going through four GPIO procedure calls
54 * per transferred bit can make performance a problem, this code
55 * is set up so that you can use it in either of two ways:
56 *
57 * - The slow generic way: set up platform_data to hold the GPIO
58 * numbers used for MISO/MOSI/SCK, and issue procedure calls for
59 * each of them. This driver can handle several such busses.
60 *
61 * - The quicker inlined way: only helps with platform GPIO code
62 * that inlines operations for constant GPIOs. This can give
63 * you tight (fast!) inner loops, but each such bus needs a
64 * new driver. You'll define a new C file, with Makefile and
65 * Kconfig support; the C code can be a total of six lines:
66 *
67 * #define DRIVER_NAME "myboard_spi2"
68 * #define SPI_MISO_GPIO 119
69 * #define SPI_MOSI_GPIO 120
70 * #define SPI_SCK_GPIO 121
71 * #define SPI_N_CHIPSEL 4
72 * #include "spi_gpio.c"
73 */
74
75#ifndef DRIVER_NAME
76#define DRIVER_NAME "spi_gpio"
77
78#define GENERIC_BITBANG /* vs tight inlines */
79
80/* all functions referencing these symbols must define pdata */
81#define SPI_MISO_GPIO ((pdata)->miso)
82#define SPI_MOSI_GPIO ((pdata)->mosi)
83#define SPI_SCK_GPIO ((pdata)->sck)
84
85#define SPI_N_CHIPSEL ((pdata)->num_chipselect)
86
87#endif
88
89/*----------------------------------------------------------------------*/
90
91static inline const struct spi_gpio_platform_data * __pure
92spi_to_pdata(const struct spi_device *spi)
93{
94 const struct spi_bitbang *bang;
95 const struct spi_gpio *spi_gpio;
96
97 bang = spi_master_get_devdata(spi->master);
98 spi_gpio = container_of(bang, struct spi_gpio, bitbang);
99 return &spi_gpio->pdata;
100}
101
102/* this is #defined to avoid unused-variable warnings when inlining */
103#define pdata spi_to_pdata(spi)
104
105static inline void setsck(const struct spi_device *spi, int is_on)
106{
107 gpio_set_value(SPI_SCK_GPIO, is_on);
108}
109
110static inline void setmosi(const struct spi_device *spi, int is_on)
111{
112 gpio_set_value(SPI_MOSI_GPIO, is_on);
113}
114
115static inline int getmiso(const struct spi_device *spi)
116{
Michael Bueschbe503442009-02-18 14:48:41 -0800117 return !!gpio_get_value(SPI_MISO_GPIO);
David Brownelld29389d2009-01-06 14:41:41 -0800118}
119
120#undef pdata
121
122/*
123 * NOTE: this clocks "as fast as we can". It "should" be a function of the
124 * requested device clock. Software overhead means we usually have trouble
125 * reaching even one Mbit/sec (except when we can inline bitops), so for now
126 * we'll just assume we never need additional per-bit slowdowns.
127 */
128#define spidelay(nsecs) do {} while (0)
129
130#define EXPAND_BITBANG_TXRX
131#include <linux/spi/spi_bitbang.h>
132
133/*
134 * These functions can leverage inline expansion of GPIO calls to shrink
135 * costs for a txrx bit, often by factors of around ten (by instruction
136 * count). That is particularly visible for larger word sizes, but helps
137 * even with default 8-bit words.
138 *
139 * REVISIT overheads calling these functions for each word also have
140 * significant performance costs. Having txrx_bufs() calls that inline
141 * the txrx_word() logic would help performance, e.g. on larger blocks
142 * used with flash storage or MMC/SD. There should also be ways to make
143 * GCC be less stupid about reloading registers inside the I/O loops,
144 * even without inlined GPIO calls; __attribute__((hot)) on GCC 4.3?
145 */
146
147static u32 spi_gpio_txrx_word_mode0(struct spi_device *spi,
148 unsigned nsecs, u32 word, u8 bits)
149{
150 return bitbang_txrx_be_cpha0(spi, nsecs, 0, word, bits);
151}
152
153static u32 spi_gpio_txrx_word_mode1(struct spi_device *spi,
154 unsigned nsecs, u32 word, u8 bits)
155{
156 return bitbang_txrx_be_cpha1(spi, nsecs, 0, word, bits);
157}
158
159static u32 spi_gpio_txrx_word_mode2(struct spi_device *spi,
160 unsigned nsecs, u32 word, u8 bits)
161{
162 return bitbang_txrx_be_cpha0(spi, nsecs, 1, word, bits);
163}
164
165static u32 spi_gpio_txrx_word_mode3(struct spi_device *spi,
166 unsigned nsecs, u32 word, u8 bits)
167{
168 return bitbang_txrx_be_cpha1(spi, nsecs, 1, word, bits);
169}
170
171/*----------------------------------------------------------------------*/
172
173static void spi_gpio_chipselect(struct spi_device *spi, int is_active)
174{
175 unsigned long cs = (unsigned long) spi->controller_data;
176
177 /* set initial clock polarity */
178 if (is_active)
179 setsck(spi, spi->mode & SPI_CPOL);
180
Michael Bueschbfb9bcd2009-04-02 16:57:07 -0700181 if (cs != SPI_GPIO_NO_CHIPSELECT) {
182 /* SPI is normally active-low */
183 gpio_set_value(cs, (spi->mode & SPI_CS_HIGH) ? is_active : !is_active);
184 }
David Brownelld29389d2009-01-06 14:41:41 -0800185}
186
187static int spi_gpio_setup(struct spi_device *spi)
188{
189 unsigned long cs = (unsigned long) spi->controller_data;
190 int status = 0;
191
192 if (spi->bits_per_word > 32)
193 return -EINVAL;
194
195 if (!spi->controller_state) {
Michael Bueschbfb9bcd2009-04-02 16:57:07 -0700196 if (cs != SPI_GPIO_NO_CHIPSELECT) {
197 status = gpio_request(cs, dev_name(&spi->dev));
198 if (status)
199 return status;
200 status = gpio_direction_output(cs, spi->mode & SPI_CS_HIGH);
201 }
David Brownelld29389d2009-01-06 14:41:41 -0800202 }
203 if (!status)
204 status = spi_bitbang_setup(spi);
205 if (status) {
Michael Bueschbfb9bcd2009-04-02 16:57:07 -0700206 if (!spi->controller_state && cs != SPI_GPIO_NO_CHIPSELECT)
David Brownelld29389d2009-01-06 14:41:41 -0800207 gpio_free(cs);
208 }
209 return status;
210}
211
212static void spi_gpio_cleanup(struct spi_device *spi)
213{
214 unsigned long cs = (unsigned long) spi->controller_data;
215
Michael Bueschbfb9bcd2009-04-02 16:57:07 -0700216 if (cs != SPI_GPIO_NO_CHIPSELECT)
217 gpio_free(cs);
David Brownelld29389d2009-01-06 14:41:41 -0800218 spi_bitbang_cleanup(spi);
219}
220
221static int __init spi_gpio_alloc(unsigned pin, const char *label, bool is_in)
222{
223 int value;
224
225 value = gpio_request(pin, label);
226 if (value == 0) {
227 if (is_in)
228 value = gpio_direction_input(pin);
229 else
230 value = gpio_direction_output(pin, 0);
231 }
232 return value;
233}
234
235static int __init
236spi_gpio_request(struct spi_gpio_platform_data *pdata, const char *label)
237{
238 int value;
239
240 /* NOTE: SPI_*_GPIO symbols may reference "pdata" */
241
242 value = spi_gpio_alloc(SPI_MOSI_GPIO, label, false);
243 if (value)
244 goto done;
245
246 value = spi_gpio_alloc(SPI_MISO_GPIO, label, true);
247 if (value)
248 goto free_mosi;
249
250 value = spi_gpio_alloc(SPI_SCK_GPIO, label, false);
251 if (value)
252 goto free_miso;
253
254 goto done;
255
256free_miso:
257 gpio_free(SPI_MISO_GPIO);
258free_mosi:
259 gpio_free(SPI_MOSI_GPIO);
260done:
261 return value;
262}
263
264static int __init spi_gpio_probe(struct platform_device *pdev)
265{
266 int status;
267 struct spi_master *master;
268 struct spi_gpio *spi_gpio;
269 struct spi_gpio_platform_data *pdata;
270
271 pdata = pdev->dev.platform_data;
272#ifdef GENERIC_BITBANG
273 if (!pdata || !pdata->num_chipselect)
274 return -ENODEV;
275#endif
276
277 status = spi_gpio_request(pdata, dev_name(&pdev->dev));
278 if (status < 0)
279 return status;
280
281 master = spi_alloc_master(&pdev->dev, sizeof *spi_gpio);
282 if (!master) {
283 status = -ENOMEM;
284 goto gpio_free;
285 }
286 spi_gpio = spi_master_get_devdata(master);
287 platform_set_drvdata(pdev, spi_gpio);
288
289 spi_gpio->pdev = pdev;
290 if (pdata)
291 spi_gpio->pdata = *pdata;
292
293 master->bus_num = pdev->id;
294 master->num_chipselect = SPI_N_CHIPSEL;
295 master->setup = spi_gpio_setup;
296 master->cleanup = spi_gpio_cleanup;
297
298 spi_gpio->bitbang.master = spi_master_get(master);
299 spi_gpio->bitbang.chipselect = spi_gpio_chipselect;
300 spi_gpio->bitbang.txrx_word[SPI_MODE_0] = spi_gpio_txrx_word_mode0;
301 spi_gpio->bitbang.txrx_word[SPI_MODE_1] = spi_gpio_txrx_word_mode1;
302 spi_gpio->bitbang.txrx_word[SPI_MODE_2] = spi_gpio_txrx_word_mode2;
303 spi_gpio->bitbang.txrx_word[SPI_MODE_3] = spi_gpio_txrx_word_mode3;
304 spi_gpio->bitbang.setup_transfer = spi_bitbang_setup_transfer;
305 spi_gpio->bitbang.flags = SPI_CS_HIGH;
306
307 status = spi_bitbang_start(&spi_gpio->bitbang);
308 if (status < 0) {
309 spi_master_put(spi_gpio->bitbang.master);
310gpio_free:
311 gpio_free(SPI_MISO_GPIO);
312 gpio_free(SPI_MOSI_GPIO);
313 gpio_free(SPI_SCK_GPIO);
314 spi_master_put(master);
315 }
316
317 return status;
318}
319
320static int __exit spi_gpio_remove(struct platform_device *pdev)
321{
322 struct spi_gpio *spi_gpio;
323 struct spi_gpio_platform_data *pdata;
324 int status;
325
326 spi_gpio = platform_get_drvdata(pdev);
327 pdata = pdev->dev.platform_data;
328
329 /* stop() unregisters child devices too */
330 status = spi_bitbang_stop(&spi_gpio->bitbang);
331 spi_master_put(spi_gpio->bitbang.master);
332
333 platform_set_drvdata(pdev, NULL);
334
335 gpio_free(SPI_MISO_GPIO);
336 gpio_free(SPI_MOSI_GPIO);
337 gpio_free(SPI_SCK_GPIO);
338
339 return status;
340}
341
342MODULE_ALIAS("platform:" DRIVER_NAME);
343
344static struct platform_driver spi_gpio_driver = {
345 .driver.name = DRIVER_NAME,
346 .driver.owner = THIS_MODULE,
347 .remove = __exit_p(spi_gpio_remove),
348};
349
350static int __init spi_gpio_init(void)
351{
352 return platform_driver_probe(&spi_gpio_driver, spi_gpio_probe);
353}
354module_init(spi_gpio_init);
355
356static void __exit spi_gpio_exit(void)
357{
358 platform_driver_unregister(&spi_gpio_driver);
359}
360module_exit(spi_gpio_exit);
361
362
363MODULE_DESCRIPTION("SPI master driver using generic bitbanged GPIO ");
364MODULE_AUTHOR("David Brownell");
365MODULE_LICENSE("GPL");