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authorDavid Brownell <dbrownell@users.sourceforge.net>2009-01-06 17:41:41 -0500
committerLinus Torvalds <torvalds@linux-foundation.org>2009-01-06 18:59:19 -0500
commitd29389de0b0ee1715333bafc6ac3f22a75aa4313 (patch)
tree6c4321359bd10231532d6cb2141f06070d8ddfd6 /drivers/spi/spi_gpio.c
parentc2bacfc44f4b8d03dbaad5d2dca2fb4161e81975 (diff)
spi_gpio driver
Generalize the old at91rm9200 "bootstrap" bitbanging SPI master driver as "spi_gpio", so it works with arbitrary GPIOs and can be configured through platform_data. Such SPI masters support: - any number of bus instances (bus_num is the platform_device.id) - any number of chipselects (one GPIO per spi_device) - all four SPI_MODE values, and SPI_CS_HIGH - i/o word sizes from 1 to 32 bits; - devices configured as with any other spi_master controller When configured using platform_data, this provides relatively low clock rates. On platforms that support inlined GPIO calls, significantly improved transfer speeds are also possible with a semi-custom driver. (It's still painful when accessing flash memory, but less so.) Sanity checked by using this version to replace both native controllers on a board with six different SPI slaves, relying on three different SPI_MODE_* values and both SPI_CS_HIGH settings for correct operation. [akpm@linux-foundation.org: cleanups] Signed-off-by: David Brownell <dbrownell@users.sourceforge.net> Acked-by: Magnus Damm <damm@igel.co.jp> Tested-by: Magnus Damm <damm@igel.co.jp> Cc: Torgil Svensson <torgil.svensson@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'drivers/spi/spi_gpio.c')
-rw-r--r--drivers/spi/spi_gpio.c360
1 files changed, 360 insertions, 0 deletions
diff --git a/drivers/spi/spi_gpio.c b/drivers/spi/spi_gpio.c
new file mode 100644
index 000000000000..49698cabc30d
--- /dev/null
+++ b/drivers/spi/spi_gpio.c
@@ -0,0 +1,360 @@
1/*
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{
117 return gpio_get_value(SPI_MISO_GPIO);
118}
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
181 /* SPI is normally active-low */
182 gpio_set_value(cs, (spi->mode & SPI_CS_HIGH) ? is_active : !is_active);
183}
184
185static int spi_gpio_setup(struct spi_device *spi)
186{
187 unsigned long cs = (unsigned long) spi->controller_data;
188 int status = 0;
189
190 if (spi->bits_per_word > 32)
191 return -EINVAL;
192
193 if (!spi->controller_state) {
194 status = gpio_request(cs, spi->dev.bus_id);
195 if (status)
196 return status;
197 status = gpio_direction_output(cs, spi->mode & SPI_CS_HIGH);
198 }
199 if (!status)
200 status = spi_bitbang_setup(spi);
201 if (status) {
202 if (!spi->controller_state)
203 gpio_free(cs);
204 }
205 return status;
206}
207
208static void spi_gpio_cleanup(struct spi_device *spi)
209{
210 unsigned long cs = (unsigned long) spi->controller_data;
211
212 gpio_free(cs);
213 spi_bitbang_cleanup(spi);
214}
215
216static int __init spi_gpio_alloc(unsigned pin, const char *label, bool is_in)
217{
218 int value;
219
220 value = gpio_request(pin, label);
221 if (value == 0) {
222 if (is_in)
223 value = gpio_direction_input(pin);
224 else
225 value = gpio_direction_output(pin, 0);
226 }
227 return value;
228}
229
230static int __init
231spi_gpio_request(struct spi_gpio_platform_data *pdata, const char *label)
232{
233 int value;
234
235 /* NOTE: SPI_*_GPIO symbols may reference "pdata" */
236
237 value = spi_gpio_alloc(SPI_MOSI_GPIO, label, false);
238 if (value)
239 goto done;
240
241 value = spi_gpio_alloc(SPI_MISO_GPIO, label, true);
242 if (value)
243 goto free_mosi;
244
245 value = spi_gpio_alloc(SPI_SCK_GPIO, label, false);
246 if (value)
247 goto free_miso;
248
249 goto done;
250
251free_miso:
252 gpio_free(SPI_MISO_GPIO);
253free_mosi:
254 gpio_free(SPI_MOSI_GPIO);
255done:
256 return value;
257}
258
259static int __init spi_gpio_probe(struct platform_device *pdev)
260{
261 int status;
262 struct spi_master *master;
263 struct spi_gpio *spi_gpio;
264 struct spi_gpio_platform_data *pdata;
265
266 pdata = pdev->dev.platform_data;
267#ifdef GENERIC_BITBANG
268 if (!pdata || !pdata->num_chipselect)
269 return -ENODEV;
270#endif
271
272 status = spi_gpio_request(pdata, dev_name(&pdev->dev));
273 if (status < 0)
274 return status;
275
276 master = spi_alloc_master(&pdev->dev, sizeof *spi_gpio);
277 if (!master) {
278 status = -ENOMEM;
279 goto gpio_free;
280 }
281 spi_gpio = spi_master_get_devdata(master);
282 platform_set_drvdata(pdev, spi_gpio);
283
284 spi_gpio->pdev = pdev;
285 if (pdata)
286 spi_gpio->pdata = *pdata;
287
288 master->bus_num = pdev->id;
289 master->num_chipselect = SPI_N_CHIPSEL;
290 master->setup = spi_gpio_setup;
291 master->cleanup = spi_gpio_cleanup;
292
293 spi_gpio->bitbang.master = spi_master_get(master);
294 spi_gpio->bitbang.chipselect = spi_gpio_chipselect;
295 spi_gpio->bitbang.txrx_word[SPI_MODE_0] = spi_gpio_txrx_word_mode0;
296 spi_gpio->bitbang.txrx_word[SPI_MODE_1] = spi_gpio_txrx_word_mode1;
297 spi_gpio->bitbang.txrx_word[SPI_MODE_2] = spi_gpio_txrx_word_mode2;
298 spi_gpio->bitbang.txrx_word[SPI_MODE_3] = spi_gpio_txrx_word_mode3;
299 spi_gpio->bitbang.setup_transfer = spi_bitbang_setup_transfer;
300 spi_gpio->bitbang.flags = SPI_CS_HIGH;
301
302 status = spi_bitbang_start(&spi_gpio->bitbang);
303 if (status < 0) {
304 spi_master_put(spi_gpio->bitbang.master);
305gpio_free:
306 gpio_free(SPI_MISO_GPIO);
307 gpio_free(SPI_MOSI_GPIO);
308 gpio_free(SPI_SCK_GPIO);
309 spi_master_put(master);
310 }
311
312 return status;
313}
314
315static int __exit spi_gpio_remove(struct platform_device *pdev)
316{
317 struct spi_gpio *spi_gpio;
318 struct spi_gpio_platform_data *pdata;
319 int status;
320
321 spi_gpio = platform_get_drvdata(pdev);
322 pdata = pdev->dev.platform_data;
323
324 /* stop() unregisters child devices too */
325 status = spi_bitbang_stop(&spi_gpio->bitbang);
326 spi_master_put(spi_gpio->bitbang.master);
327
328 platform_set_drvdata(pdev, NULL);
329
330 gpio_free(SPI_MISO_GPIO);
331 gpio_free(SPI_MOSI_GPIO);
332 gpio_free(SPI_SCK_GPIO);
333
334 return status;
335}
336
337MODULE_ALIAS("platform:" DRIVER_NAME);
338
339static struct platform_driver spi_gpio_driver = {
340 .driver.name = DRIVER_NAME,
341 .driver.owner = THIS_MODULE,
342 .remove = __exit_p(spi_gpio_remove),
343};
344
345static int __init spi_gpio_init(void)
346{
347 return platform_driver_probe(&spi_gpio_driver, spi_gpio_probe);
348}
349module_init(spi_gpio_init);
350
351static void __exit spi_gpio_exit(void)
352{
353 platform_driver_unregister(&spi_gpio_driver);
354}
355module_exit(spi_gpio_exit);
356
357
358MODULE_DESCRIPTION("SPI master driver using generic bitbanged GPIO ");
359MODULE_AUTHOR("David Brownell");
360MODULE_LICENSE("GPL");