Root/drivers/spi/spi-gpio.c

1/*
2 * 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/module.h>
22#include <linux/init.h>
23#include <linux/platform_device.h>
24#include <linux/gpio.h>
25
26#include <linux/spi/spi.h>
27#include <linux/spi/spi_bitbang.h>
28#include <linux/spi/spi_gpio.h>
29
30
31/*
32 * This bitbanging SPI master driver should help make systems usable
33 * when a native hardware SPI engine is not available, perhaps because
34 * its driver isn't yet working or because the I/O pins it requires
35 * are used for other purposes.
36 *
37 * platform_device->driver_data ... points to spi_gpio
38 *
39 * spi->controller_state ... reserved for bitbang framework code
40 * spi->controller_data ... holds chipselect GPIO
41 *
42 * spi->master->dev.driver_data ... points to spi_gpio->bitbang
43 */
44
45struct spi_gpio {
46    struct spi_bitbang bitbang;
47    struct spi_gpio_platform_data pdata;
48    struct platform_device *pdev;
49};
50
51/*----------------------------------------------------------------------*/
52
53/*
54 * Because the overhead of going through four GPIO procedure calls
55 * per transferred bit can make performance a problem, this code
56 * is set up so that you can use it in either of two ways:
57 *
58 * - The slow generic way: set up platform_data to hold the GPIO
59 * numbers used for MISO/MOSI/SCK, and issue procedure calls for
60 * each of them. This driver can handle several such busses.
61 *
62 * - The quicker inlined way: only helps with platform GPIO code
63 * that inlines operations for constant GPIOs. This can give
64 * you tight (fast!) inner loops, but each such bus needs a
65 * new driver. You'll define a new C file, with Makefile and
66 * Kconfig support; the C code can be a total of six lines:
67 *
68 * #define DRIVER_NAME "myboard_spi2"
69 * #define SPI_MISO_GPIO 119
70 * #define SPI_MOSI_GPIO 120
71 * #define SPI_SCK_GPIO 121
72 * #define SPI_N_CHIPSEL 4
73 * #include "spi-gpio.c"
74 */
75
76#ifndef DRIVER_NAME
77#define DRIVER_NAME "spi_gpio"
78
79#define GENERIC_BITBANG /* vs tight inlines */
80
81/* all functions referencing these symbols must define pdata */
82#define SPI_MISO_GPIO ((pdata)->miso)
83#define SPI_MOSI_GPIO ((pdata)->mosi)
84#define SPI_SCK_GPIO ((pdata)->sck)
85
86#define SPI_N_CHIPSEL ((pdata)->num_chipselect)
87
88#endif
89
90/*----------------------------------------------------------------------*/
91
92static inline const struct spi_gpio_platform_data * __pure
93spi_to_pdata(const struct spi_device *spi)
94{
95    const struct spi_bitbang *bang;
96    const struct spi_gpio *spi_gpio;
97
98    bang = spi_master_get_devdata(spi->master);
99    spi_gpio = container_of(bang, struct spi_gpio, bitbang);
100    return &spi_gpio->pdata;
101}
102
103/* this is #defined to avoid unused-variable warnings when inlining */
104#define pdata spi_to_pdata(spi)
105
106static inline void setsck(const struct spi_device *spi, int is_on)
107{
108    gpio_set_value(SPI_SCK_GPIO, is_on);
109}
110
111static inline void setmosi(const struct spi_device *spi, int is_on)
112{
113    gpio_set_value(SPI_MOSI_GPIO, is_on);
114}
115
116static inline int getmiso(const struct spi_device *spi)
117{
118    return !!gpio_get_value(SPI_MISO_GPIO);
119}
120
121#undef pdata
122
123/*
124 * NOTE: this clocks "as fast as we can". It "should" be a function of the
125 * requested device clock. Software overhead means we usually have trouble
126 * reaching even one Mbit/sec (except when we can inline bitops), so for now
127 * we'll just assume we never need additional per-bit slowdowns.
128 */
129#define spidelay(nsecs) do {} while (0)
130
131#include "spi-bitbang-txrx.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, 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, 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, 0, 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, 0, word, bits);
169}
170
171/*
172 * These functions do not call setmosi or getmiso if respective flag
173 * (SPI_MASTER_NO_RX or SPI_MASTER_NO_TX) is set, so they are safe to
174 * call when such pin is not present or defined in the controller.
175 * A separate set of callbacks is defined to get highest possible
176 * speed in the generic case (when both MISO and MOSI lines are
177 * available), as optimiser will remove the checks when argument is
178 * constant.
179 */
180
181static u32 spi_gpio_spec_txrx_word_mode0(struct spi_device *spi,
182        unsigned nsecs, u32 word, u8 bits)
183{
184    unsigned flags = spi->master->flags;
185    return bitbang_txrx_be_cpha0(spi, nsecs, 0, flags, word, bits);
186}
187
188static u32 spi_gpio_spec_txrx_word_mode1(struct spi_device *spi,
189        unsigned nsecs, u32 word, u8 bits)
190{
191    unsigned flags = spi->master->flags;
192    return bitbang_txrx_be_cpha1(spi, nsecs, 0, flags, word, bits);
193}
194
195static u32 spi_gpio_spec_txrx_word_mode2(struct spi_device *spi,
196        unsigned nsecs, u32 word, u8 bits)
197{
198    unsigned flags = spi->master->flags;
199    return bitbang_txrx_be_cpha0(spi, nsecs, 1, flags, word, bits);
200}
201
202static u32 spi_gpio_spec_txrx_word_mode3(struct spi_device *spi,
203        unsigned nsecs, u32 word, u8 bits)
204{
205    unsigned flags = spi->master->flags;
206    return bitbang_txrx_be_cpha1(spi, nsecs, 1, flags, word, bits);
207}
208
209/*----------------------------------------------------------------------*/
210
211static void spi_gpio_chipselect(struct spi_device *spi, int is_active)
212{
213    unsigned long cs = (unsigned long) spi->controller_data;
214
215    /* set initial clock polarity */
216    if (is_active)
217        setsck(spi, spi->mode & SPI_CPOL);
218
219    if (cs != SPI_GPIO_NO_CHIPSELECT) {
220        /* SPI is normally active-low */
221        gpio_set_value(cs, (spi->mode & SPI_CS_HIGH) ? is_active : !is_active);
222    }
223}
224
225static int spi_gpio_setup(struct spi_device *spi)
226{
227    unsigned long cs = (unsigned long) spi->controller_data;
228    int status = 0;
229
230    if (spi->bits_per_word > 32)
231        return -EINVAL;
232
233    if (!spi->controller_state) {
234        if (cs != SPI_GPIO_NO_CHIPSELECT) {
235            status = gpio_request(cs, dev_name(&spi->dev));
236            if (status)
237                return status;
238            status = gpio_direction_output(cs,
239                    !(spi->mode & SPI_CS_HIGH));
240        }
241    }
242    if (!status)
243        status = spi_bitbang_setup(spi);
244    if (status) {
245        if (!spi->controller_state && cs != SPI_GPIO_NO_CHIPSELECT)
246            gpio_free(cs);
247    }
248    return status;
249}
250
251static void spi_gpio_cleanup(struct spi_device *spi)
252{
253    unsigned long cs = (unsigned long) spi->controller_data;
254
255    if (cs != SPI_GPIO_NO_CHIPSELECT)
256        gpio_free(cs);
257    spi_bitbang_cleanup(spi);
258}
259
260static int __devinit spi_gpio_alloc(unsigned pin, const char *label, bool is_in)
261{
262    int value;
263
264    value = gpio_request(pin, label);
265    if (value == 0) {
266        if (is_in)
267            value = gpio_direction_input(pin);
268        else
269            value = gpio_direction_output(pin, 0);
270    }
271    return value;
272}
273
274static int __devinit
275spi_gpio_request(struct spi_gpio_platform_data *pdata, const char *label,
276    u16 *res_flags)
277{
278    int value;
279
280    /* NOTE: SPI_*_GPIO symbols may reference "pdata" */
281
282    if (SPI_MOSI_GPIO != SPI_GPIO_NO_MOSI) {
283        value = spi_gpio_alloc(SPI_MOSI_GPIO, label, false);
284        if (value)
285            goto done;
286    } else {
287        /* HW configuration without MOSI pin */
288        *res_flags |= SPI_MASTER_NO_TX;
289    }
290
291    if (SPI_MISO_GPIO != SPI_GPIO_NO_MISO) {
292        value = spi_gpio_alloc(SPI_MISO_GPIO, label, true);
293        if (value)
294            goto free_mosi;
295    } else {
296        /* HW configuration without MISO pin */
297        *res_flags |= SPI_MASTER_NO_RX;
298    }
299
300    value = spi_gpio_alloc(SPI_SCK_GPIO, label, false);
301    if (value)
302        goto free_miso;
303
304    goto done;
305
306free_miso:
307    if (SPI_MISO_GPIO != SPI_GPIO_NO_MISO)
308        gpio_free(SPI_MISO_GPIO);
309free_mosi:
310    if (SPI_MOSI_GPIO != SPI_GPIO_NO_MOSI)
311        gpio_free(SPI_MOSI_GPIO);
312done:
313    return value;
314}
315
316static int __devinit spi_gpio_probe(struct platform_device *pdev)
317{
318    int status;
319    struct spi_master *master;
320    struct spi_gpio *spi_gpio;
321    struct spi_gpio_platform_data *pdata;
322    u16 master_flags = 0;
323
324    pdata = pdev->dev.platform_data;
325#ifdef GENERIC_BITBANG
326    if (!pdata || !pdata->num_chipselect)
327        return -ENODEV;
328#endif
329
330    status = spi_gpio_request(pdata, dev_name(&pdev->dev), &master_flags);
331    if (status < 0)
332        return status;
333
334    master = spi_alloc_master(&pdev->dev, sizeof *spi_gpio);
335    if (!master) {
336        status = -ENOMEM;
337        goto gpio_free;
338    }
339    spi_gpio = spi_master_get_devdata(master);
340    platform_set_drvdata(pdev, spi_gpio);
341
342    spi_gpio->pdev = pdev;
343    if (pdata)
344        spi_gpio->pdata = *pdata;
345
346    master->flags = master_flags;
347    master->bus_num = pdev->id;
348    master->num_chipselect = SPI_N_CHIPSEL;
349    master->setup = spi_gpio_setup;
350    master->cleanup = spi_gpio_cleanup;
351
352    spi_gpio->bitbang.master = spi_master_get(master);
353    spi_gpio->bitbang.chipselect = spi_gpio_chipselect;
354
355    if ((master_flags & (SPI_MASTER_NO_TX | SPI_MASTER_NO_RX)) == 0) {
356        spi_gpio->bitbang.txrx_word[SPI_MODE_0] = spi_gpio_txrx_word_mode0;
357        spi_gpio->bitbang.txrx_word[SPI_MODE_1] = spi_gpio_txrx_word_mode1;
358        spi_gpio->bitbang.txrx_word[SPI_MODE_2] = spi_gpio_txrx_word_mode2;
359        spi_gpio->bitbang.txrx_word[SPI_MODE_3] = spi_gpio_txrx_word_mode3;
360    } else {
361        spi_gpio->bitbang.txrx_word[SPI_MODE_0] = spi_gpio_spec_txrx_word_mode0;
362        spi_gpio->bitbang.txrx_word[SPI_MODE_1] = spi_gpio_spec_txrx_word_mode1;
363        spi_gpio->bitbang.txrx_word[SPI_MODE_2] = spi_gpio_spec_txrx_word_mode2;
364        spi_gpio->bitbang.txrx_word[SPI_MODE_3] = spi_gpio_spec_txrx_word_mode3;
365    }
366    spi_gpio->bitbang.setup_transfer = spi_bitbang_setup_transfer;
367    spi_gpio->bitbang.flags = SPI_CS_HIGH;
368
369    status = spi_bitbang_start(&spi_gpio->bitbang);
370    if (status < 0) {
371        spi_master_put(spi_gpio->bitbang.master);
372gpio_free:
373        if (SPI_MISO_GPIO != SPI_GPIO_NO_MISO)
374            gpio_free(SPI_MISO_GPIO);
375        if (SPI_MOSI_GPIO != SPI_GPIO_NO_MOSI)
376            gpio_free(SPI_MOSI_GPIO);
377        gpio_free(SPI_SCK_GPIO);
378        spi_master_put(master);
379    }
380
381    return status;
382}
383
384static int __devexit spi_gpio_remove(struct platform_device *pdev)
385{
386    struct spi_gpio *spi_gpio;
387    struct spi_gpio_platform_data *pdata;
388    int status;
389
390    spi_gpio = platform_get_drvdata(pdev);
391    pdata = pdev->dev.platform_data;
392
393    /* stop() unregisters child devices too */
394    status = spi_bitbang_stop(&spi_gpio->bitbang);
395    spi_master_put(spi_gpio->bitbang.master);
396
397    platform_set_drvdata(pdev, NULL);
398
399    if (SPI_MISO_GPIO != SPI_GPIO_NO_MISO)
400        gpio_free(SPI_MISO_GPIO);
401    if (SPI_MOSI_GPIO != SPI_GPIO_NO_MOSI)
402        gpio_free(SPI_MOSI_GPIO);
403    gpio_free(SPI_SCK_GPIO);
404
405    return status;
406}
407
408MODULE_ALIAS("platform:" DRIVER_NAME);
409
410static struct platform_driver spi_gpio_driver = {
411    .driver.name = DRIVER_NAME,
412    .driver.owner = THIS_MODULE,
413    .probe = spi_gpio_probe,
414    .remove = __devexit_p(spi_gpio_remove),
415};
416module_platform_driver(spi_gpio_driver);
417
418MODULE_DESCRIPTION("SPI master driver using generic bitbanged GPIO ");
419MODULE_AUTHOR("David Brownell");
420MODULE_LICENSE("GPL");
421

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