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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
hartleys41c42212010-05-06 20:51:04 +0000130#include "spi_bitbang_txrx.h"
David Brownelld29389d2009-01-06 14:41:41 -0800131
132/*
133 * These functions can leverage inline expansion of GPIO calls to shrink
134 * costs for a txrx bit, often by factors of around ten (by instruction
135 * count). That is particularly visible for larger word sizes, but helps
136 * even with default 8-bit words.
137 *
138 * REVISIT overheads calling these functions for each word also have
139 * significant performance costs. Having txrx_bufs() calls that inline
140 * the txrx_word() logic would help performance, e.g. on larger blocks
141 * used with flash storage or MMC/SD. There should also be ways to make
142 * GCC be less stupid about reloading registers inside the I/O loops,
143 * even without inlined GPIO calls; __attribute__((hot)) on GCC 4.3?
144 */
145
146static u32 spi_gpio_txrx_word_mode0(struct spi_device *spi,
147 unsigned nsecs, u32 word, u8 bits)
148{
149 return bitbang_txrx_be_cpha0(spi, nsecs, 0, word, bits);
150}
151
152static u32 spi_gpio_txrx_word_mode1(struct spi_device *spi,
153 unsigned nsecs, u32 word, u8 bits)
154{
155 return bitbang_txrx_be_cpha1(spi, nsecs, 0, word, bits);
156}
157
158static u32 spi_gpio_txrx_word_mode2(struct spi_device *spi,
159 unsigned nsecs, u32 word, u8 bits)
160{
161 return bitbang_txrx_be_cpha0(spi, nsecs, 1, word, bits);
162}
163
164static u32 spi_gpio_txrx_word_mode3(struct spi_device *spi,
165 unsigned nsecs, u32 word, u8 bits)
166{
167 return bitbang_txrx_be_cpha1(spi, nsecs, 1, word, bits);
168}
169
170/*----------------------------------------------------------------------*/
171
172static void spi_gpio_chipselect(struct spi_device *spi, int is_active)
173{
174 unsigned long cs = (unsigned long) spi->controller_data;
175
176 /* set initial clock polarity */
177 if (is_active)
178 setsck(spi, spi->mode & SPI_CPOL);
179
Michael Bueschbfb9bcd2009-04-02 16:57:07 -0700180 if (cs != SPI_GPIO_NO_CHIPSELECT) {
181 /* SPI is normally active-low */
182 gpio_set_value(cs, (spi->mode & SPI_CS_HIGH) ? is_active : !is_active);
183 }
David Brownelld29389d2009-01-06 14:41:41 -0800184}
185
186static int spi_gpio_setup(struct spi_device *spi)
187{
188 unsigned long cs = (unsigned long) spi->controller_data;
189 int status = 0;
190
191 if (spi->bits_per_word > 32)
192 return -EINVAL;
193
194 if (!spi->controller_state) {
Michael Bueschbfb9bcd2009-04-02 16:57:07 -0700195 if (cs != SPI_GPIO_NO_CHIPSELECT) {
196 status = gpio_request(cs, dev_name(&spi->dev));
197 if (status)
198 return status;
199 status = gpio_direction_output(cs, spi->mode & SPI_CS_HIGH);
200 }
David Brownelld29389d2009-01-06 14:41:41 -0800201 }
202 if (!status)
203 status = spi_bitbang_setup(spi);
204 if (status) {
Michael Bueschbfb9bcd2009-04-02 16:57:07 -0700205 if (!spi->controller_state && cs != SPI_GPIO_NO_CHIPSELECT)
David Brownelld29389d2009-01-06 14:41:41 -0800206 gpio_free(cs);
207 }
208 return status;
209}
210
211static void spi_gpio_cleanup(struct spi_device *spi)
212{
213 unsigned long cs = (unsigned long) spi->controller_data;
214
Michael Bueschbfb9bcd2009-04-02 16:57:07 -0700215 if (cs != SPI_GPIO_NO_CHIPSELECT)
216 gpio_free(cs);
David Brownelld29389d2009-01-06 14:41:41 -0800217 spi_bitbang_cleanup(spi);
218}
219
220static int __init spi_gpio_alloc(unsigned pin, const char *label, bool is_in)
221{
222 int value;
223
224 value = gpio_request(pin, label);
225 if (value == 0) {
226 if (is_in)
227 value = gpio_direction_input(pin);
228 else
229 value = gpio_direction_output(pin, 0);
230 }
231 return value;
232}
233
234static int __init
235spi_gpio_request(struct spi_gpio_platform_data *pdata, const char *label)
236{
237 int value;
238
239 /* NOTE: SPI_*_GPIO symbols may reference "pdata" */
240
241 value = spi_gpio_alloc(SPI_MOSI_GPIO, label, false);
242 if (value)
243 goto done;
244
245 value = spi_gpio_alloc(SPI_MISO_GPIO, label, true);
246 if (value)
247 goto free_mosi;
248
249 value = spi_gpio_alloc(SPI_SCK_GPIO, label, false);
250 if (value)
251 goto free_miso;
252
253 goto done;
254
255free_miso:
256 gpio_free(SPI_MISO_GPIO);
257free_mosi:
258 gpio_free(SPI_MOSI_GPIO);
259done:
260 return value;
261}
262
263static int __init spi_gpio_probe(struct platform_device *pdev)
264{
265 int status;
266 struct spi_master *master;
267 struct spi_gpio *spi_gpio;
268 struct spi_gpio_platform_data *pdata;
269
270 pdata = pdev->dev.platform_data;
271#ifdef GENERIC_BITBANG
272 if (!pdata || !pdata->num_chipselect)
273 return -ENODEV;
274#endif
275
276 status = spi_gpio_request(pdata, dev_name(&pdev->dev));
277 if (status < 0)
278 return status;
279
280 master = spi_alloc_master(&pdev->dev, sizeof *spi_gpio);
281 if (!master) {
282 status = -ENOMEM;
283 goto gpio_free;
284 }
285 spi_gpio = spi_master_get_devdata(master);
286 platform_set_drvdata(pdev, spi_gpio);
287
288 spi_gpio->pdev = pdev;
289 if (pdata)
290 spi_gpio->pdata = *pdata;
291
292 master->bus_num = pdev->id;
293 master->num_chipselect = SPI_N_CHIPSEL;
294 master->setup = spi_gpio_setup;
295 master->cleanup = spi_gpio_cleanup;
296
297 spi_gpio->bitbang.master = spi_master_get(master);
298 spi_gpio->bitbang.chipselect = spi_gpio_chipselect;
299 spi_gpio->bitbang.txrx_word[SPI_MODE_0] = spi_gpio_txrx_word_mode0;
300 spi_gpio->bitbang.txrx_word[SPI_MODE_1] = spi_gpio_txrx_word_mode1;
301 spi_gpio->bitbang.txrx_word[SPI_MODE_2] = spi_gpio_txrx_word_mode2;
302 spi_gpio->bitbang.txrx_word[SPI_MODE_3] = spi_gpio_txrx_word_mode3;
303 spi_gpio->bitbang.setup_transfer = spi_bitbang_setup_transfer;
304 spi_gpio->bitbang.flags = SPI_CS_HIGH;
305
306 status = spi_bitbang_start(&spi_gpio->bitbang);
307 if (status < 0) {
308 spi_master_put(spi_gpio->bitbang.master);
309gpio_free:
310 gpio_free(SPI_MISO_GPIO);
311 gpio_free(SPI_MOSI_GPIO);
312 gpio_free(SPI_SCK_GPIO);
313 spi_master_put(master);
314 }
315
316 return status;
317}
318
319static int __exit spi_gpio_remove(struct platform_device *pdev)
320{
321 struct spi_gpio *spi_gpio;
322 struct spi_gpio_platform_data *pdata;
323 int status;
324
325 spi_gpio = platform_get_drvdata(pdev);
326 pdata = pdev->dev.platform_data;
327
328 /* stop() unregisters child devices too */
329 status = spi_bitbang_stop(&spi_gpio->bitbang);
330 spi_master_put(spi_gpio->bitbang.master);
331
332 platform_set_drvdata(pdev, NULL);
333
334 gpio_free(SPI_MISO_GPIO);
335 gpio_free(SPI_MOSI_GPIO);
336 gpio_free(SPI_SCK_GPIO);
337
338 return status;
339}
340
341MODULE_ALIAS("platform:" DRIVER_NAME);
342
343static struct platform_driver spi_gpio_driver = {
344 .driver.name = DRIVER_NAME,
345 .driver.owner = THIS_MODULE,
346 .remove = __exit_p(spi_gpio_remove),
347};
348
349static int __init spi_gpio_init(void)
350{
351 return platform_driver_probe(&spi_gpio_driver, spi_gpio_probe);
352}
353module_init(spi_gpio_init);
354
355static void __exit spi_gpio_exit(void)
356{
357 platform_driver_unregister(&spi_gpio_driver);
358}
359module_exit(spi_gpio_exit);
360
361
362MODULE_DESCRIPTION("SPI master driver using generic bitbanged GPIO ");
363MODULE_AUTHOR("David Brownell");
364MODULE_LICENSE("GPL");