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;
39 struct gpio_desc **cs_gpios;
42 /*----------------------------------------------------------------------*/
45 * Because the overhead of going through four GPIO procedure calls
46 * per transferred bit can make performance a problem, this code
47 * is set up so that you can use it in either of two ways:
49 * - The slow generic way: set up platform_data to hold the GPIO
50 * numbers used for MISO/MOSI/SCK, and issue procedure calls for
51 * each of them. This driver can handle several such busses.
53 * - The quicker inlined way: only helps with platform GPIO code
54 * that inlines operations for constant GPIOs. This can give
55 * you tight (fast!) inner loops, but each such bus needs a
56 * new driver. You'll define a new C file, with Makefile and
57 * Kconfig support; the C code can be a total of six lines:
59 * #define DRIVER_NAME "myboard_spi2"
60 * #define SPI_MISO_GPIO 119
61 * #define SPI_MOSI_GPIO 120
62 * #define SPI_SCK_GPIO 121
63 * #define SPI_N_CHIPSEL 4
64 * #include "spi-gpio.c"
68 #define DRIVER_NAME "spi_gpio"
70 #define GENERIC_BITBANG /* vs tight inlines */
74 /*----------------------------------------------------------------------*/
76 static inline struct spi_gpio *__pure
77 spi_to_spi_gpio(const struct spi_device *spi)
79 const struct spi_bitbang *bang;
80 struct spi_gpio *spi_gpio;
82 bang = spi_master_get_devdata(spi->master);
83 spi_gpio = container_of(bang, struct spi_gpio, bitbang);
87 /* These helpers are in turn called by the bitbang inlines */
88 static inline void setsck(const struct spi_device *spi, int is_on)
90 struct spi_gpio *spi_gpio = spi_to_spi_gpio(spi);
92 gpiod_set_value_cansleep(spi_gpio->sck, is_on);
95 static inline void setmosi(const struct spi_device *spi, int is_on)
97 struct spi_gpio *spi_gpio = spi_to_spi_gpio(spi);
99 gpiod_set_value_cansleep(spi_gpio->mosi, is_on);
102 static inline int getmiso(const struct spi_device *spi)
104 struct spi_gpio *spi_gpio = spi_to_spi_gpio(spi);
106 if (spi->mode & SPI_3WIRE)
107 return !!gpiod_get_value_cansleep(spi_gpio->mosi);
109 return !!gpiod_get_value_cansleep(spi_gpio->miso);
113 * NOTE: this clocks "as fast as we can". It "should" be a function of the
114 * requested device clock. Software overhead means we usually have trouble
115 * reaching even one Mbit/sec (except when we can inline bitops), so for now
116 * we'll just assume we never need additional per-bit slowdowns.
118 #define spidelay(nsecs) do {} while (0)
120 #include "spi-bitbang-txrx.h"
123 * These functions can leverage inline expansion of GPIO calls to shrink
124 * costs for a txrx bit, often by factors of around ten (by instruction
125 * count). That is particularly visible for larger word sizes, but helps
126 * even with default 8-bit words.
128 * REVISIT overheads calling these functions for each word also have
129 * significant performance costs. Having txrx_bufs() calls that inline
130 * the txrx_word() logic would help performance, e.g. on larger blocks
131 * used with flash storage or MMC/SD. There should also be ways to make
132 * GCC be less stupid about reloading registers inside the I/O loops,
133 * even without inlined GPIO calls; __attribute__((hot)) on GCC 4.3?
136 static u32 spi_gpio_txrx_word_mode0(struct spi_device *spi,
137 unsigned nsecs, u32 word, u8 bits, unsigned flags)
139 return bitbang_txrx_be_cpha0(spi, nsecs, 0, flags, word, bits);
142 static u32 spi_gpio_txrx_word_mode1(struct spi_device *spi,
143 unsigned nsecs, u32 word, u8 bits, unsigned flags)
145 return bitbang_txrx_be_cpha1(spi, nsecs, 0, flags, word, bits);
148 static u32 spi_gpio_txrx_word_mode2(struct spi_device *spi,
149 unsigned nsecs, u32 word, u8 bits, unsigned flags)
151 return bitbang_txrx_be_cpha0(spi, nsecs, 1, flags, word, bits);
154 static u32 spi_gpio_txrx_word_mode3(struct spi_device *spi,
155 unsigned nsecs, u32 word, u8 bits, unsigned flags)
157 return bitbang_txrx_be_cpha1(spi, nsecs, 1, flags, word, bits);
161 * These functions do not call setmosi or getmiso if respective flag
162 * (SPI_MASTER_NO_RX or SPI_MASTER_NO_TX) is set, so they are safe to
163 * call when such pin is not present or defined in the controller.
164 * A separate set of callbacks is defined to get highest possible
165 * speed in the generic case (when both MISO and MOSI lines are
166 * available), as optimiser will remove the checks when argument is
170 static u32 spi_gpio_spec_txrx_word_mode0(struct spi_device *spi,
171 unsigned nsecs, u32 word, u8 bits, unsigned flags)
173 flags = spi->master->flags;
174 return bitbang_txrx_be_cpha0(spi, nsecs, 0, flags, word, bits);
177 static u32 spi_gpio_spec_txrx_word_mode1(struct spi_device *spi,
178 unsigned nsecs, u32 word, u8 bits, unsigned flags)
180 flags = spi->master->flags;
181 return bitbang_txrx_be_cpha1(spi, nsecs, 0, flags, word, bits);
184 static u32 spi_gpio_spec_txrx_word_mode2(struct spi_device *spi,
185 unsigned nsecs, u32 word, u8 bits, unsigned flags)
187 flags = spi->master->flags;
188 return bitbang_txrx_be_cpha0(spi, nsecs, 1, flags, word, bits);
191 static u32 spi_gpio_spec_txrx_word_mode3(struct spi_device *spi,
192 unsigned nsecs, u32 word, u8 bits, unsigned flags)
194 flags = spi->master->flags;
195 return bitbang_txrx_be_cpha1(spi, nsecs, 1, flags, word, bits);
198 /*----------------------------------------------------------------------*/
200 static void spi_gpio_chipselect(struct spi_device *spi, int is_active)
202 struct spi_gpio *spi_gpio = spi_to_spi_gpio(spi);
204 /* set initial clock line level */
206 if (spi_gpio->sck_idle_input)
207 gpiod_direction_output(spi_gpio->sck, spi->mode & SPI_CPOL);
209 gpiod_set_value_cansleep(spi_gpio->sck, spi->mode & SPI_CPOL);
212 /* Drive chip select line, if we have one */
213 if (spi_gpio->cs_gpios) {
214 struct gpio_desc *cs = spi_gpio->cs_gpios[spi->chip_select];
216 /* SPI chip selects are normally active-low */
217 gpiod_set_value_cansleep(cs, (spi->mode & SPI_CS_HIGH) ? is_active : !is_active);
220 if (spi_gpio->sck_idle_input && !is_active)
221 gpiod_direction_input(spi_gpio->sck);
224 static int spi_gpio_setup(struct spi_device *spi)
226 struct gpio_desc *cs;
228 struct spi_gpio *spi_gpio = spi_to_spi_gpio(spi);
231 * The CS GPIOs have already been
232 * initialized from the descriptor lookup.
234 if (spi_gpio->cs_gpios) {
235 cs = spi_gpio->cs_gpios[spi->chip_select];
236 if (!spi->controller_state && cs)
237 status = gpiod_direction_output(cs,
238 !(spi->mode & SPI_CS_HIGH));
242 status = spi_bitbang_setup(spi);
247 static int spi_gpio_set_direction(struct spi_device *spi, bool output)
249 struct spi_gpio *spi_gpio = spi_to_spi_gpio(spi);
253 return gpiod_direction_output(spi_gpio->mosi, 1);
255 ret = gpiod_direction_input(spi_gpio->mosi);
259 * Send a turnaround high impedance cycle when switching
260 * from output to input. Theoretically there should be
261 * a clock delay here, but as has been noted above, the
262 * nsec delay function for bit-banged GPIO is simply
263 * {} because bit-banging just doesn't get fast enough
266 if (spi->mode & SPI_3WIRE_HIZ) {
267 gpiod_set_value_cansleep(spi_gpio->sck,
268 !(spi->mode & SPI_CPOL));
269 gpiod_set_value_cansleep(spi_gpio->sck,
270 !!(spi->mode & SPI_CPOL));
275 static void spi_gpio_cleanup(struct spi_device *spi)
277 spi_bitbang_cleanup(spi);
281 * It can be convenient to use this driver with pins that have alternate
282 * functions associated with a "native" SPI controller if a driver for that
283 * controller is not available, or is missing important functionality.
285 * On platforms which can do so, configure MISO with a weak pullup unless
286 * there's an external pullup on that signal. That saves power by avoiding
287 * floating signals. (A weak pulldown would save power too, but many
288 * drivers expect to see all-ones data as the no slave "response".)
290 static int spi_gpio_request(struct device *dev, struct spi_gpio *spi_gpio)
292 spi_gpio->mosi = devm_gpiod_get_optional(dev, "mosi", GPIOD_OUT_LOW);
293 if (IS_ERR(spi_gpio->mosi))
294 return PTR_ERR(spi_gpio->mosi);
296 spi_gpio->miso = devm_gpiod_get_optional(dev, "miso", GPIOD_IN);
297 if (IS_ERR(spi_gpio->miso))
298 return PTR_ERR(spi_gpio->miso);
300 spi_gpio->sck_idle_input = device_property_read_bool(dev, "sck-idle-input");
301 spi_gpio->sck = devm_gpiod_get(dev, "sck", GPIOD_OUT_LOW);
302 return PTR_ERR_OR_ZERO(spi_gpio->sck);
306 static const struct of_device_id spi_gpio_dt_ids[] = {
307 { .compatible = "spi-gpio" },
310 MODULE_DEVICE_TABLE(of, spi_gpio_dt_ids);
312 static int spi_gpio_probe_dt(struct platform_device *pdev,
313 struct spi_master *master)
315 master->dev.of_node = pdev->dev.of_node;
316 master->use_gpio_descriptors = true;
321 static inline int spi_gpio_probe_dt(struct platform_device *pdev,
322 struct spi_master *master)
328 static int spi_gpio_probe_pdata(struct platform_device *pdev,
329 struct spi_master *master)
331 struct device *dev = &pdev->dev;
332 struct spi_gpio_platform_data *pdata = dev_get_platdata(dev);
333 struct spi_gpio *spi_gpio = spi_master_get_devdata(master);
336 #ifdef GENERIC_BITBANG
337 if (!pdata || !pdata->num_chipselect)
341 * The master needs to think there is a chipselect even if not
344 master->num_chipselect = pdata->num_chipselect ?: 1;
346 spi_gpio->cs_gpios = devm_kcalloc(dev, master->num_chipselect,
347 sizeof(*spi_gpio->cs_gpios),
349 if (!spi_gpio->cs_gpios)
352 for (i = 0; i < master->num_chipselect; i++) {
353 spi_gpio->cs_gpios[i] = devm_gpiod_get_index(dev, "cs", i,
355 if (IS_ERR(spi_gpio->cs_gpios[i]))
356 return PTR_ERR(spi_gpio->cs_gpios[i]);
362 static int spi_gpio_probe(struct platform_device *pdev)
365 struct spi_master *master;
366 struct spi_gpio *spi_gpio;
367 struct device *dev = &pdev->dev;
368 struct spi_bitbang *bb;
370 master = devm_spi_alloc_master(dev, sizeof(*spi_gpio));
374 if (pdev->dev.of_node)
375 status = spi_gpio_probe_dt(pdev, master);
377 status = spi_gpio_probe_pdata(pdev, master);
382 spi_gpio = spi_master_get_devdata(master);
384 status = spi_gpio_request(dev, spi_gpio);
388 master->bits_per_word_mask = SPI_BPW_RANGE_MASK(1, 32);
389 master->mode_bits = SPI_3WIRE | SPI_3WIRE_HIZ | SPI_CPHA | SPI_CPOL |
391 if (!spi_gpio->mosi) {
392 /* HW configuration without MOSI pin
394 * No setting SPI_MASTER_NO_RX here - if there is only
395 * a MOSI pin connected the host can still do RX by
396 * changing the direction of the line.
398 master->flags = SPI_MASTER_NO_TX;
401 master->bus_num = pdev->id;
402 master->setup = spi_gpio_setup;
403 master->cleanup = spi_gpio_cleanup;
405 bb = &spi_gpio->bitbang;
408 * There is some additional business, apart from driving the CS GPIO
409 * line, that we need to do on selection. This makes the local
410 * callback for chipselect always get called.
412 master->flags |= SPI_MASTER_GPIO_SS;
413 bb->chipselect = spi_gpio_chipselect;
414 bb->set_line_direction = spi_gpio_set_direction;
416 if (master->flags & SPI_MASTER_NO_TX) {
417 bb->txrx_word[SPI_MODE_0] = spi_gpio_spec_txrx_word_mode0;
418 bb->txrx_word[SPI_MODE_1] = spi_gpio_spec_txrx_word_mode1;
419 bb->txrx_word[SPI_MODE_2] = spi_gpio_spec_txrx_word_mode2;
420 bb->txrx_word[SPI_MODE_3] = spi_gpio_spec_txrx_word_mode3;
422 bb->txrx_word[SPI_MODE_0] = spi_gpio_txrx_word_mode0;
423 bb->txrx_word[SPI_MODE_1] = spi_gpio_txrx_word_mode1;
424 bb->txrx_word[SPI_MODE_2] = spi_gpio_txrx_word_mode2;
425 bb->txrx_word[SPI_MODE_3] = spi_gpio_txrx_word_mode3;
427 bb->setup_transfer = spi_bitbang_setup_transfer;
429 status = spi_bitbang_init(&spi_gpio->bitbang);
433 return devm_spi_register_master(&pdev->dev, master);
436 MODULE_ALIAS("platform:" DRIVER_NAME);
438 static struct platform_driver spi_gpio_driver = {
441 .of_match_table = of_match_ptr(spi_gpio_dt_ids),
443 .probe = spi_gpio_probe,
445 module_platform_driver(spi_gpio_driver);
447 MODULE_DESCRIPTION("SPI master driver using generic bitbanged GPIO ");
448 MODULE_AUTHOR("David Brownell");
449 MODULE_LICENSE("GPL");