1 // SPDX-License-Identifier: GPL-2.0-or-later
3 * SPI master driver using generic bitbanged GPIO
5 * Copyright (C) 2006,2008 David Brownell
6 * Copyright (C) 2017 Linus Walleij
8 #include <linux/kernel.h>
9 #include <linux/module.h>
10 #include <linux/platform_device.h>
11 #include <linux/gpio/consumer.h>
13 #include <linux/of_device.h>
15 #include <linux/spi/spi.h>
16 #include <linux/spi/spi_bitbang.h>
17 #include <linux/spi/spi_gpio.h>
21 * This bitbanging SPI master driver should help make systems usable
22 * when a native hardware SPI engine is not available, perhaps because
23 * its driver isn't yet working or because the I/O pins it requires
24 * are used for other purposes.
26 * platform_device->driver_data ... points to spi_gpio
28 * spi->controller_state ... reserved for bitbang framework code
30 * spi->master->dev.driver_data ... points to spi_gpio->bitbang
34 struct spi_bitbang bitbang;
35 struct gpio_desc *sck;
36 struct gpio_desc *miso;
37 struct gpio_desc *mosi;
38 struct gpio_desc **cs_gpios;
41 /*----------------------------------------------------------------------*/
44 * Because the overhead of going through four GPIO procedure calls
45 * per transferred bit can make performance a problem, this code
46 * is set up so that you can use it in either of two ways:
48 * - The slow generic way: set up platform_data to hold the GPIO
49 * numbers used for MISO/MOSI/SCK, and issue procedure calls for
50 * each of them. This driver can handle several such busses.
52 * - The quicker inlined way: only helps with platform GPIO code
53 * that inlines operations for constant GPIOs. This can give
54 * you tight (fast!) inner loops, but each such bus needs a
55 * new driver. You'll define a new C file, with Makefile and
56 * Kconfig support; the C code can be a total of six lines:
58 * #define DRIVER_NAME "myboard_spi2"
59 * #define SPI_MISO_GPIO 119
60 * #define SPI_MOSI_GPIO 120
61 * #define SPI_SCK_GPIO 121
62 * #define SPI_N_CHIPSEL 4
63 * #include "spi-gpio.c"
67 #define DRIVER_NAME "spi_gpio"
69 #define GENERIC_BITBANG /* vs tight inlines */
73 /*----------------------------------------------------------------------*/
75 static inline struct spi_gpio *__pure
76 spi_to_spi_gpio(const struct spi_device *spi)
78 const struct spi_bitbang *bang;
79 struct spi_gpio *spi_gpio;
81 bang = spi_master_get_devdata(spi->master);
82 spi_gpio = container_of(bang, struct spi_gpio, bitbang);
86 /* These helpers are in turn called by the bitbang inlines */
87 static inline void setsck(const struct spi_device *spi, int is_on)
89 struct spi_gpio *spi_gpio = spi_to_spi_gpio(spi);
91 gpiod_set_value_cansleep(spi_gpio->sck, is_on);
94 static inline void setmosi(const struct spi_device *spi, int is_on)
96 struct spi_gpio *spi_gpio = spi_to_spi_gpio(spi);
98 gpiod_set_value_cansleep(spi_gpio->mosi, is_on);
101 static inline int getmiso(const struct spi_device *spi)
103 struct spi_gpio *spi_gpio = spi_to_spi_gpio(spi);
105 if (spi->mode & SPI_3WIRE)
106 return !!gpiod_get_value_cansleep(spi_gpio->mosi);
108 return !!gpiod_get_value_cansleep(spi_gpio->miso);
112 * NOTE: this clocks "as fast as we can". It "should" be a function of the
113 * requested device clock. Software overhead means we usually have trouble
114 * reaching even one Mbit/sec (except when we can inline bitops), so for now
115 * we'll just assume we never need additional per-bit slowdowns.
117 #define spidelay(nsecs) do {} while (0)
119 #include "spi-bitbang-txrx.h"
122 * These functions can leverage inline expansion of GPIO calls to shrink
123 * costs for a txrx bit, often by factors of around ten (by instruction
124 * count). That is particularly visible for larger word sizes, but helps
125 * even with default 8-bit words.
127 * REVISIT overheads calling these functions for each word also have
128 * significant performance costs. Having txrx_bufs() calls that inline
129 * the txrx_word() logic would help performance, e.g. on larger blocks
130 * used with flash storage or MMC/SD. There should also be ways to make
131 * GCC be less stupid about reloading registers inside the I/O loops,
132 * even without inlined GPIO calls; __attribute__((hot)) on GCC 4.3?
135 static u32 spi_gpio_txrx_word_mode0(struct spi_device *spi,
136 unsigned nsecs, u32 word, u8 bits, unsigned flags)
138 return bitbang_txrx_be_cpha0(spi, nsecs, 0, flags, word, bits);
141 static u32 spi_gpio_txrx_word_mode1(struct spi_device *spi,
142 unsigned nsecs, u32 word, u8 bits, unsigned flags)
144 return bitbang_txrx_be_cpha1(spi, nsecs, 0, flags, word, bits);
147 static u32 spi_gpio_txrx_word_mode2(struct spi_device *spi,
148 unsigned nsecs, u32 word, u8 bits, unsigned flags)
150 return bitbang_txrx_be_cpha0(spi, nsecs, 1, flags, word, bits);
153 static u32 spi_gpio_txrx_word_mode3(struct spi_device *spi,
154 unsigned nsecs, u32 word, u8 bits, unsigned flags)
156 return bitbang_txrx_be_cpha1(spi, nsecs, 1, flags, word, bits);
160 * These functions do not call setmosi or getmiso if respective flag
161 * (SPI_MASTER_NO_RX or SPI_MASTER_NO_TX) is set, so they are safe to
162 * call when such pin is not present or defined in the controller.
163 * A separate set of callbacks is defined to get highest possible
164 * speed in the generic case (when both MISO and MOSI lines are
165 * available), as optimiser will remove the checks when argument is
169 static u32 spi_gpio_spec_txrx_word_mode0(struct spi_device *spi,
170 unsigned nsecs, u32 word, u8 bits, unsigned flags)
172 flags = spi->master->flags;
173 return bitbang_txrx_be_cpha0(spi, nsecs, 0, flags, word, bits);
176 static u32 spi_gpio_spec_txrx_word_mode1(struct spi_device *spi,
177 unsigned nsecs, u32 word, u8 bits, unsigned flags)
179 flags = spi->master->flags;
180 return bitbang_txrx_be_cpha1(spi, nsecs, 0, flags, word, bits);
183 static u32 spi_gpio_spec_txrx_word_mode2(struct spi_device *spi,
184 unsigned nsecs, u32 word, u8 bits, unsigned flags)
186 flags = spi->master->flags;
187 return bitbang_txrx_be_cpha0(spi, nsecs, 1, flags, word, bits);
190 static u32 spi_gpio_spec_txrx_word_mode3(struct spi_device *spi,
191 unsigned nsecs, u32 word, u8 bits, unsigned flags)
193 flags = spi->master->flags;
194 return bitbang_txrx_be_cpha1(spi, nsecs, 1, flags, word, bits);
197 /*----------------------------------------------------------------------*/
199 static void spi_gpio_chipselect(struct spi_device *spi, int is_active)
201 struct spi_gpio *spi_gpio = spi_to_spi_gpio(spi);
203 /* set initial clock line level */
205 gpiod_set_value_cansleep(spi_gpio->sck, spi->mode & SPI_CPOL);
207 /* Drive chip select line, if we have one */
208 if (spi_gpio->cs_gpios) {
209 struct gpio_desc *cs = spi_gpio->cs_gpios[spi->chip_select];
211 /* SPI chip selects are normally active-low */
212 gpiod_set_value_cansleep(cs, (spi->mode & SPI_CS_HIGH) ? is_active : !is_active);
216 static int spi_gpio_setup(struct spi_device *spi)
218 struct gpio_desc *cs;
220 struct spi_gpio *spi_gpio = spi_to_spi_gpio(spi);
223 * The CS GPIOs have already been
224 * initialized from the descriptor lookup.
226 if (spi_gpio->cs_gpios) {
227 cs = spi_gpio->cs_gpios[spi->chip_select];
228 if (!spi->controller_state && cs)
229 status = gpiod_direction_output(cs,
230 !(spi->mode & SPI_CS_HIGH));
234 status = spi_bitbang_setup(spi);
239 static int spi_gpio_set_direction(struct spi_device *spi, bool output)
241 struct spi_gpio *spi_gpio = spi_to_spi_gpio(spi);
245 return gpiod_direction_output(spi_gpio->mosi, 1);
248 * Only change MOSI to an input if using 3WIRE mode.
249 * Otherwise, MOSI could be left floating if there is
250 * no pull resistor connected to the I/O pin, or could
251 * be left logic high if there is a pull-up. Transmitting
252 * logic high when only clocking MISO data in can put some
253 * SPI devices in to a bad state.
255 if (spi->mode & SPI_3WIRE) {
256 ret = gpiod_direction_input(spi_gpio->mosi);
261 * Send a turnaround high impedance cycle when switching
262 * from output to input. Theoretically there should be
263 * a clock delay here, but as has been noted above, the
264 * nsec delay function for bit-banged GPIO is simply
265 * {} because bit-banging just doesn't get fast enough
268 if (spi->mode & SPI_3WIRE_HIZ) {
269 gpiod_set_value_cansleep(spi_gpio->sck,
270 !(spi->mode & SPI_CPOL));
271 gpiod_set_value_cansleep(spi_gpio->sck,
272 !!(spi->mode & SPI_CPOL));
277 static void spi_gpio_cleanup(struct spi_device *spi)
279 spi_bitbang_cleanup(spi);
283 * It can be convenient to use this driver with pins that have alternate
284 * functions associated with a "native" SPI controller if a driver for that
285 * controller is not available, or is missing important functionality.
287 * On platforms which can do so, configure MISO with a weak pullup unless
288 * there's an external pullup on that signal. That saves power by avoiding
289 * floating signals. (A weak pulldown would save power too, but many
290 * drivers expect to see all-ones data as the no slave "response".)
292 static int spi_gpio_request(struct device *dev, struct spi_gpio *spi_gpio)
294 spi_gpio->mosi = devm_gpiod_get_optional(dev, "mosi", GPIOD_OUT_LOW);
295 if (IS_ERR(spi_gpio->mosi))
296 return PTR_ERR(spi_gpio->mosi);
298 spi_gpio->miso = devm_gpiod_get_optional(dev, "miso", GPIOD_IN);
299 if (IS_ERR(spi_gpio->miso))
300 return PTR_ERR(spi_gpio->miso);
302 spi_gpio->sck = devm_gpiod_get(dev, "sck", GPIOD_OUT_LOW);
303 return PTR_ERR_OR_ZERO(spi_gpio->sck);
307 static const struct of_device_id spi_gpio_dt_ids[] = {
308 { .compatible = "spi-gpio" },
311 MODULE_DEVICE_TABLE(of, spi_gpio_dt_ids);
313 static int spi_gpio_probe_dt(struct platform_device *pdev,
314 struct spi_master *master)
316 master->dev.of_node = pdev->dev.of_node;
317 master->use_gpio_descriptors = true;
322 static inline int spi_gpio_probe_dt(struct platform_device *pdev,
323 struct spi_master *master)
329 static int spi_gpio_probe_pdata(struct platform_device *pdev,
330 struct spi_master *master)
332 struct device *dev = &pdev->dev;
333 struct spi_gpio_platform_data *pdata = dev_get_platdata(dev);
334 struct spi_gpio *spi_gpio = spi_master_get_devdata(master);
337 #ifdef GENERIC_BITBANG
338 if (!pdata || !pdata->num_chipselect)
342 * The master needs to think there is a chipselect even if not
345 master->num_chipselect = pdata->num_chipselect ?: 1;
347 spi_gpio->cs_gpios = devm_kcalloc(dev, master->num_chipselect,
348 sizeof(*spi_gpio->cs_gpios),
350 if (!spi_gpio->cs_gpios)
353 for (i = 0; i < master->num_chipselect; i++) {
354 spi_gpio->cs_gpios[i] = devm_gpiod_get_index(dev, "cs", i,
356 if (IS_ERR(spi_gpio->cs_gpios[i]))
357 return PTR_ERR(spi_gpio->cs_gpios[i]);
363 static int spi_gpio_probe(struct platform_device *pdev)
366 struct spi_master *master;
367 struct spi_gpio *spi_gpio;
368 struct device *dev = &pdev->dev;
369 struct spi_bitbang *bb;
371 master = devm_spi_alloc_master(dev, sizeof(*spi_gpio));
375 if (pdev->dev.of_node)
376 status = spi_gpio_probe_dt(pdev, master);
378 status = spi_gpio_probe_pdata(pdev, master);
383 spi_gpio = spi_master_get_devdata(master);
385 status = spi_gpio_request(dev, spi_gpio);
389 master->bits_per_word_mask = SPI_BPW_RANGE_MASK(1, 32);
390 master->mode_bits = SPI_3WIRE | SPI_3WIRE_HIZ | SPI_CPHA | SPI_CPOL |
392 if (!spi_gpio->mosi) {
393 /* HW configuration without MOSI pin
395 * No setting SPI_MASTER_NO_RX here - if there is only
396 * a MOSI pin connected the host can still do RX by
397 * changing the direction of the line.
399 master->flags = SPI_MASTER_NO_TX;
402 master->bus_num = pdev->id;
403 master->setup = spi_gpio_setup;
404 master->cleanup = spi_gpio_cleanup;
406 bb = &spi_gpio->bitbang;
409 * There is some additional business, apart from driving the CS GPIO
410 * line, that we need to do on selection. This makes the local
411 * callback for chipselect always get called.
413 master->flags |= SPI_MASTER_GPIO_SS;
414 bb->chipselect = spi_gpio_chipselect;
415 bb->set_line_direction = spi_gpio_set_direction;
417 if (master->flags & SPI_MASTER_NO_TX) {
418 bb->txrx_word[SPI_MODE_0] = spi_gpio_spec_txrx_word_mode0;
419 bb->txrx_word[SPI_MODE_1] = spi_gpio_spec_txrx_word_mode1;
420 bb->txrx_word[SPI_MODE_2] = spi_gpio_spec_txrx_word_mode2;
421 bb->txrx_word[SPI_MODE_3] = spi_gpio_spec_txrx_word_mode3;
423 bb->txrx_word[SPI_MODE_0] = spi_gpio_txrx_word_mode0;
424 bb->txrx_word[SPI_MODE_1] = spi_gpio_txrx_word_mode1;
425 bb->txrx_word[SPI_MODE_2] = spi_gpio_txrx_word_mode2;
426 bb->txrx_word[SPI_MODE_3] = spi_gpio_txrx_word_mode3;
428 bb->setup_transfer = spi_bitbang_setup_transfer;
430 status = spi_bitbang_init(&spi_gpio->bitbang);
434 return devm_spi_register_master(&pdev->dev, master);
437 MODULE_ALIAS("platform:" DRIVER_NAME);
439 static struct platform_driver spi_gpio_driver = {
442 .of_match_table = of_match_ptr(spi_gpio_dt_ids),
444 .probe = spi_gpio_probe,
446 module_platform_driver(spi_gpio_driver);
448 MODULE_DESCRIPTION("SPI master driver using generic bitbanged GPIO ");
449 MODULE_AUTHOR("David Brownell");
450 MODULE_LICENSE("GPL");