2 * spi_gpio.c - SPI master driver using generic bitbanged GPIO
4 * Copyright (C) 2006,2008 David Brownell
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.
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.
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.
20 #include <linux/kernel.h>
21 #include <linux/init.h>
22 #include <linux/platform_device.h>
23 #include <linux/gpio.h>
25 #include <linux/spi/spi.h>
26 #include <linux/spi/spi_bitbang.h>
27 #include <linux/spi/spi_gpio.h>
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.
36 * platform_device->driver_data ... points to spi_gpio
38 * spi->controller_state ... reserved for bitbang framework code
39 * spi->controller_data ... holds chipselect GPIO
41 * spi->master->dev.driver_data ... points to spi_gpio->bitbang
45 struct spi_bitbang bitbang
;
46 struct spi_gpio_platform_data pdata
;
47 struct platform_device
*pdev
;
50 /*----------------------------------------------------------------------*/
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:
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.
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:
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"
76 #define DRIVER_NAME "spi_gpio"
78 #define GENERIC_BITBANG /* vs tight inlines */
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)
85 #define SPI_N_CHIPSEL ((pdata)->num_chipselect)
89 /*----------------------------------------------------------------------*/
91 static inline const struct spi_gpio_platform_data
* __pure
92 spi_to_pdata(const struct spi_device
*spi
)
94 const struct spi_bitbang
*bang
;
95 const struct spi_gpio
*spi_gpio
;
97 bang
= spi_master_get_devdata(spi
->master
);
98 spi_gpio
= container_of(bang
, struct spi_gpio
, bitbang
);
99 return &spi_gpio
->pdata
;
102 /* this is #defined to avoid unused-variable warnings when inlining */
103 #define pdata spi_to_pdata(spi)
105 static inline void setsck(const struct spi_device
*spi
, int is_on
)
107 gpio_set_value(SPI_SCK_GPIO
, is_on
);
110 static inline void setmosi(const struct spi_device
*spi
, int is_on
)
112 gpio_set_value(SPI_MOSI_GPIO
, is_on
);
115 static inline int getmiso(const struct spi_device
*spi
)
117 return !!gpio_get_value(SPI_MISO_GPIO
);
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.
128 #define spidelay(nsecs) do {} while (0)
130 #define EXPAND_BITBANG_TXRX
131 #include <linux/spi/spi_bitbang.h>
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.
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?
147 static u32
spi_gpio_txrx_word_mode0(struct spi_device
*spi
,
148 unsigned nsecs
, u32 word
, u8 bits
)
150 return bitbang_txrx_be_cpha0(spi
, nsecs
, 0, word
, bits
);
153 static u32
spi_gpio_txrx_word_mode1(struct spi_device
*spi
,
154 unsigned nsecs
, u32 word
, u8 bits
)
156 return bitbang_txrx_be_cpha1(spi
, nsecs
, 0, word
, bits
);
159 static u32
spi_gpio_txrx_word_mode2(struct spi_device
*spi
,
160 unsigned nsecs
, u32 word
, u8 bits
)
162 return bitbang_txrx_be_cpha0(spi
, nsecs
, 1, word
, bits
);
165 static u32
spi_gpio_txrx_word_mode3(struct spi_device
*spi
,
166 unsigned nsecs
, u32 word
, u8 bits
)
168 return bitbang_txrx_be_cpha1(spi
, nsecs
, 1, word
, bits
);
171 /*----------------------------------------------------------------------*/
173 static void spi_gpio_chipselect(struct spi_device
*spi
, int is_active
)
175 unsigned long cs
= (unsigned long) spi
->controller_data
;
177 /* set initial clock polarity */
179 setsck(spi
, spi
->mode
& SPI_CPOL
);
181 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
);
187 static int spi_gpio_setup(struct spi_device
*spi
)
189 unsigned long cs
= (unsigned long) spi
->controller_data
;
192 if (spi
->bits_per_word
> 32)
195 if (!spi
->controller_state
) {
196 if (cs
!= SPI_GPIO_NO_CHIPSELECT
) {
197 status
= gpio_request(cs
, dev_name(&spi
->dev
));
200 status
= gpio_direction_output(cs
, spi
->mode
& SPI_CS_HIGH
);
204 status
= spi_bitbang_setup(spi
);
206 if (!spi
->controller_state
&& cs
!= SPI_GPIO_NO_CHIPSELECT
)
212 static void spi_gpio_cleanup(struct spi_device
*spi
)
214 unsigned long cs
= (unsigned long) spi
->controller_data
;
216 if (cs
!= SPI_GPIO_NO_CHIPSELECT
)
218 spi_bitbang_cleanup(spi
);
221 static int __init
spi_gpio_alloc(unsigned pin
, const char *label
, bool is_in
)
225 value
= gpio_request(pin
, label
);
228 value
= gpio_direction_input(pin
);
230 value
= gpio_direction_output(pin
, 0);
236 spi_gpio_request(struct spi_gpio_platform_data
*pdata
, const char *label
)
240 /* NOTE: SPI_*_GPIO symbols may reference "pdata" */
242 value
= spi_gpio_alloc(SPI_MOSI_GPIO
, label
, false);
246 value
= spi_gpio_alloc(SPI_MISO_GPIO
, label
, true);
250 value
= spi_gpio_alloc(SPI_SCK_GPIO
, label
, false);
257 gpio_free(SPI_MISO_GPIO
);
259 gpio_free(SPI_MOSI_GPIO
);
264 static int __init
spi_gpio_probe(struct platform_device
*pdev
)
267 struct spi_master
*master
;
268 struct spi_gpio
*spi_gpio
;
269 struct spi_gpio_platform_data
*pdata
;
271 pdata
= pdev
->dev
.platform_data
;
272 #ifdef GENERIC_BITBANG
273 if (!pdata
|| !pdata
->num_chipselect
)
277 status
= spi_gpio_request(pdata
, dev_name(&pdev
->dev
));
281 master
= spi_alloc_master(&pdev
->dev
, sizeof *spi_gpio
);
286 spi_gpio
= spi_master_get_devdata(master
);
287 platform_set_drvdata(pdev
, spi_gpio
);
289 spi_gpio
->pdev
= pdev
;
291 spi_gpio
->pdata
= *pdata
;
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
;
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
;
307 status
= spi_bitbang_start(&spi_gpio
->bitbang
);
309 spi_master_put(spi_gpio
->bitbang
.master
);
311 gpio_free(SPI_MISO_GPIO
);
312 gpio_free(SPI_MOSI_GPIO
);
313 gpio_free(SPI_SCK_GPIO
);
314 spi_master_put(master
);
320 static int __exit
spi_gpio_remove(struct platform_device
*pdev
)
322 struct spi_gpio
*spi_gpio
;
323 struct spi_gpio_platform_data
*pdata
;
326 spi_gpio
= platform_get_drvdata(pdev
);
327 pdata
= pdev
->dev
.platform_data
;
329 /* stop() unregisters child devices too */
330 status
= spi_bitbang_stop(&spi_gpio
->bitbang
);
331 spi_master_put(spi_gpio
->bitbang
.master
);
333 platform_set_drvdata(pdev
, NULL
);
335 gpio_free(SPI_MISO_GPIO
);
336 gpio_free(SPI_MOSI_GPIO
);
337 gpio_free(SPI_SCK_GPIO
);
342 MODULE_ALIAS("platform:" DRIVER_NAME
);
344 static struct platform_driver spi_gpio_driver
= {
345 .driver
.name
= DRIVER_NAME
,
346 .driver
.owner
= THIS_MODULE
,
347 .remove
= __exit_p(spi_gpio_remove
),
350 static int __init
spi_gpio_init(void)
352 return platform_driver_probe(&spi_gpio_driver
, spi_gpio_probe
);
354 module_init(spi_gpio_init
);
356 static void __exit
spi_gpio_exit(void)
358 platform_driver_unregister(&spi_gpio_driver
);
360 module_exit(spi_gpio_exit
);
363 MODULE_DESCRIPTION("SPI master driver using generic bitbanged GPIO ");
364 MODULE_AUTHOR("David Brownell");
365 MODULE_LICENSE("GPL");