// SPDX-License-Identifier: GPL-2.0-or-later /* * SPI master driver using generic bitbanged GPIO * * Copyright (C) 2006,2008 David Brownell * Copyright (C) 2017 Linus Walleij */ #include <linux/kernel.h> #include <linux/module.h> #include <linux/platform_device.h> #include <linux/gpio/consumer.h> #include <linux/of.h> #include <linux/of_device.h> #include <linux/spi/spi.h> #include <linux/spi/spi_bitbang.h> #include <linux/spi/spi_gpio.h> /* * This bitbanging SPI master driver should help make systems usable * when a native hardware SPI engine is not available, perhaps because * its driver isn't yet working or because the I/O pins it requires * are used for other purposes. * * platform_device->driver_data ... points to spi_gpio * * spi->controller_state ... reserved for bitbang framework code * * spi->master->dev.driver_data ... points to spi_gpio->bitbang */ struct spi_gpio { struct spi_bitbang bitbang; struct gpio_desc *sck; struct gpio_desc *miso; struct gpio_desc *mosi; struct gpio_desc **cs_gpios; }; /*----------------------------------------------------------------------*/ /* * Because the overhead of going through four GPIO procedure calls * per transferred bit can make performance a problem, this code * is set up so that you can use it in either of two ways: * * - The slow generic way: set up platform_data to hold the GPIO * numbers used for MISO/MOSI/SCK, and issue procedure calls for * each of them. This driver can handle several such busses. * * - The quicker inlined way: only helps with platform GPIO code * that inlines operations for constant GPIOs. This can give * you tight (fast!) inner loops, but each such bus needs a * new driver. You'll define a new C file, with Makefile and * Kconfig support; the C code can be a total of six lines: * * #define DRIVER_NAME "myboard_spi2" * #define SPI_MISO_GPIO 119 * #define SPI_MOSI_GPIO 120 * #define SPI_SCK_GPIO 121 * #define SPI_N_CHIPSEL 4 * #include "spi-gpio.c" */ #ifndef DRIVER_NAME #define DRIVER_NAME "spi_gpio" #define GENERIC_BITBANG /* vs tight inlines */ #endif /*----------------------------------------------------------------------*/ static inline struct spi_gpio *__pure spi_to_spi_gpio(const struct spi_device *spi) { const struct spi_bitbang *bang; struct spi_gpio *spi_gpio; bang = spi_master_get_devdata(spi->master); spi_gpio = container_of(bang, struct spi_gpio, bitbang); return spi_gpio; } /* These helpers are in turn called by the bitbang inlines */ static inline void setsck(const struct spi_device *spi, int is_on) { struct spi_gpio *spi_gpio = spi_to_spi_gpio(spi); gpiod_set_value_cansleep(spi_gpio->sck, is_on); } static inline void setmosi(const struct spi_device *spi, int is_on) { struct spi_gpio *spi_gpio = spi_to_spi_gpio(spi); gpiod_set_value_cansleep(spi_gpio->mosi, is_on); } static inline int getmiso(const struct spi_device *spi) { struct spi_gpio *spi_gpio = spi_to_spi_gpio(spi); if (spi->mode & SPI_3WIRE) return !!gpiod_get_value_cansleep(spi_gpio->mosi); else return !!gpiod_get_value_cansleep(spi_gpio->miso); } /* * NOTE: this clocks "as fast as we can". It "should" be a function of the * requested device clock. Software overhead means we usually have trouble * reaching even one Mbit/sec (except when we can inline bitops), so for now * we'll just assume we never need additional per-bit slowdowns. */ #define spidelay(nsecs) do {} while (0) #include "spi-bitbang-txrx.h" /* * These functions can leverage inline expansion of GPIO calls to shrink * costs for a txrx bit, often by factors of around ten (by instruction * count). That is particularly visible for larger word sizes, but helps * even with default 8-bit words. * * REVISIT overheads calling these functions for each word also have * significant performance costs. Having txrx_bufs() calls that inline * the txrx_word() logic would help performance, e.g. on larger blocks * used with flash storage or MMC/SD. There should also be ways to make * GCC be less stupid about reloading registers inside the I/O loops, * even without inlined GPIO calls; __attribute__((hot)) on GCC 4.3? */ static u32 spi_gpio_txrx_word_mode0(struct spi_device *spi, unsigned nsecs, u32 word, u8 bits, unsigned flags) { return bitbang_txrx_be_cpha0(spi, nsecs, 0, flags, word, bits); } static u32 spi_gpio_txrx_word_mode1(struct spi_device *spi, unsigned nsecs, u32 word, u8 bits, unsigned flags) { return bitbang_txrx_be_cpha1(spi, nsecs, 0, flags, word, bits); } static u32 spi_gpio_txrx_word_mode2(struct spi_device *spi, unsigned nsecs, u32 word, u8 bits, unsigned flags) { return bitbang_txrx_be_cpha0(spi, nsecs, 1, flags, word, bits); } static u32 spi_gpio_txrx_word_mode3(struct spi_device *spi, unsigned nsecs, u32 word, u8 bits, unsigned flags) { return bitbang_txrx_be_cpha1(spi, nsecs, 1, flags, word, bits); } /* * These functions do not call setmosi or getmiso if respective flag * (SPI_MASTER_NO_RX or SPI_MASTER_NO_TX) is set, so they are safe to * call when such pin is not present or defined in the controller. * A separate set of callbacks is defined to get highest possible * speed in the generic case (when both MISO and MOSI lines are * available), as optimiser will remove the checks when argument is * constant. */ static u32 spi_gpio_spec_txrx_word_mode0(struct spi_device *spi, unsigned nsecs, u32 word, u8 bits, unsigned flags) { flags = spi->master->flags; return bitbang_txrx_be_cpha0(spi, nsecs, 0, flags, word, bits); } static u32 spi_gpio_spec_txrx_word_mode1(struct spi_device *spi, unsigned nsecs, u32 word, u8 bits, unsigned flags) { flags = spi->master->flags; return bitbang_txrx_be_cpha1(spi, nsecs, 0, flags, word, bits); } static u32 spi_gpio_spec_txrx_word_mode2(struct spi_device *spi, unsigned nsecs, u32 word, u8 bits, unsigned flags) { flags = spi->master->flags; return bitbang_txrx_be_cpha0(spi, nsecs, 1, flags, word, bits); } static u32 spi_gpio_spec_txrx_word_mode3(struct spi_device *spi, unsigned nsecs, u32 word, u8 bits, unsigned flags) { flags = spi->master->flags; return bitbang_txrx_be_cpha1(spi, nsecs, 1, flags, word, bits); } /*----------------------------------------------------------------------*/ static void spi_gpio_chipselect(struct spi_device *spi, int is_active) { struct spi_gpio *spi_gpio = spi_to_spi_gpio(spi); /* set initial clock line level */ if (is_active) gpiod_set_value_cansleep(spi_gpio->sck, spi->mode & SPI_CPOL); /* Drive chip select line, if we have one */ if (spi_gpio->cs_gpios) { struct gpio_desc *cs = spi_gpio->cs_gpios[spi->chip_select]; /* SPI chip selects are normally active-low */ gpiod_set_value_cansleep(cs, (spi->mode & SPI_CS_HIGH) ? is_active : !is_active); } } static int spi_gpio_setup(struct spi_device *spi) { struct gpio_desc *cs; int status = 0; struct spi_gpio *spi_gpio = spi_to_spi_gpio(spi); /* * The CS GPIOs have already been * initialized from the descriptor lookup. */ if (spi_gpio->cs_gpios) { cs = spi_gpio->cs_gpios[spi->chip_select]; if (!spi->controller_state && cs) status = gpiod_direction_output(cs, !(spi->mode & SPI_CS_HIGH)); } if (!status) status = spi_bitbang_setup(spi); return status; } static int spi_gpio_set_direction(struct spi_device *spi, bool output) { struct spi_gpio *spi_gpio = spi_to_spi_gpio(spi); int ret; if (output) return gpiod_direction_output(spi_gpio->mosi, 1); ret = gpiod_direction_input(spi_gpio->mosi); if (ret) return ret; /* * Send a turnaround high impedance cycle when switching * from output to input. Theoretically there should be * a clock delay here, but as has been noted above, the * nsec delay function for bit-banged GPIO is simply * {} because bit-banging just doesn't get fast enough * anyway. */ if (spi->mode & SPI_3WIRE_HIZ) { gpiod_set_value_cansleep(spi_gpio->sck, !(spi->mode & SPI_CPOL)); gpiod_set_value_cansleep(spi_gpio->sck, !!(spi->mode & SPI_CPOL)); } return 0; } static void spi_gpio_cleanup(struct spi_device *spi) { spi_bitbang_cleanup(spi); } /* * It can be convenient to use this driver with pins that have alternate * functions associated with a "native" SPI controller if a driver for that * controller is not available, or is missing important functionality. * * On platforms which can do so, configure MISO with a weak pullup unless * there's an external pullup on that signal. That saves power by avoiding * floating signals. (A weak pulldown would save power too, but many * drivers expect to see all-ones data as the no slave "response".) */ static int spi_gpio_request(struct device *dev, struct spi_gpio *spi_gpio) { spi_gpio->mosi = devm_gpiod_get_optional(dev, "mosi", GPIOD_OUT_LOW); if (IS_ERR(spi_gpio->mosi)) return PTR_ERR(spi_gpio->mosi); spi_gpio->miso = devm_gpiod_get_optional(dev, "miso", GPIOD_IN); if (IS_ERR(spi_gpio->miso)) return PTR_ERR(spi_gpio->miso); spi_gpio->sck = devm_gpiod_get(dev, "sck", GPIOD_OUT_LOW); return PTR_ERR_OR_ZERO(spi_gpio->sck); } #ifdef CONFIG_OF static const struct of_device_id spi_gpio_dt_ids[] = { { .compatible = "spi-gpio" }, {} }; MODULE_DEVICE_TABLE(of, spi_gpio_dt_ids); static int spi_gpio_probe_dt(struct platform_device *pdev, struct spi_master *master) { master->dev.of_node = pdev->dev.of_node; master->use_gpio_descriptors = true; return 0; } #else static inline int spi_gpio_probe_dt(struct platform_device *pdev, struct spi_master *master) { return 0; } #endif static int spi_gpio_probe_pdata(struct platform_device *pdev, struct spi_master *master) { struct device *dev = &pdev->dev; struct spi_gpio_platform_data *pdata = dev_get_platdata(dev); struct spi_gpio *spi_gpio = spi_master_get_devdata(master); int i; #ifdef GENERIC_BITBANG if (!pdata || !pdata->num_chipselect) return -ENODEV; #endif /* * The master needs to think there is a chipselect even if not * connected */ master->num_chipselect = pdata->num_chipselect ?: 1; spi_gpio->cs_gpios = devm_kcalloc(dev, master->num_chipselect, sizeof(*spi_gpio->cs_gpios), GFP_KERNEL); if (!spi_gpio->cs_gpios) return -ENOMEM; for (i = 0; i < master->num_chipselect; i++) { spi_gpio->cs_gpios[i] = devm_gpiod_get_index(dev, "cs", i, GPIOD_OUT_HIGH); if (IS_ERR(spi_gpio->cs_gpios[i])) return PTR_ERR(spi_gpio->cs_gpios[i]); } return 0; } static void spi_gpio_put(void *data) { spi_master_put(data); } static int spi_gpio_probe(struct platform_device *pdev) { int status; struct spi_master *master; struct spi_gpio *spi_gpio; struct device *dev = &pdev->dev; struct spi_bitbang *bb; master = spi_alloc_master(dev, sizeof(*spi_gpio)); if (!master) return -ENOMEM; status = devm_add_action_or_reset(&pdev->dev, spi_gpio_put, master); if (status) { spi_master_put(master); return status; } if (pdev->dev.of_node) status = spi_gpio_probe_dt(pdev, master); else status = spi_gpio_probe_pdata(pdev, master); if (status) return status; spi_gpio = spi_master_get_devdata(master); status = spi_gpio_request(dev, spi_gpio); if (status) return status; master->bits_per_word_mask = SPI_BPW_RANGE_MASK(1, 32); master->mode_bits = SPI_3WIRE | SPI_3WIRE_HIZ | SPI_CPHA | SPI_CPOL | SPI_CS_HIGH; if (!spi_gpio->mosi) { /* HW configuration without MOSI pin * * No setting SPI_MASTER_NO_RX here - if there is only * a MOSI pin connected the host can still do RX by * changing the direction of the line. */ master->flags = SPI_MASTER_NO_TX; } master->bus_num = pdev->id; master->setup = spi_gpio_setup; master->cleanup = spi_gpio_cleanup; bb = &spi_gpio->bitbang; bb->master = master; /* * There is some additional business, apart from driving the CS GPIO * line, that we need to do on selection. This makes the local * callback for chipselect always get called. */ master->flags |= SPI_MASTER_GPIO_SS; bb->chipselect = spi_gpio_chipselect; bb->set_line_direction = spi_gpio_set_direction; if (master->flags & SPI_MASTER_NO_TX) { bb->txrx_word[SPI_MODE_0] = spi_gpio_spec_txrx_word_mode0; bb->txrx_word[SPI_MODE_1] = spi_gpio_spec_txrx_word_mode1; bb->txrx_word[SPI_MODE_2] = spi_gpio_spec_txrx_word_mode2; bb->txrx_word[SPI_MODE_3] = spi_gpio_spec_txrx_word_mode3; } else { bb->txrx_word[SPI_MODE_0] = spi_gpio_txrx_word_mode0; bb->txrx_word[SPI_MODE_1] = spi_gpio_txrx_word_mode1; bb->txrx_word[SPI_MODE_2] = spi_gpio_txrx_word_mode2; bb->txrx_word[SPI_MODE_3] = spi_gpio_txrx_word_mode3; } bb->setup_transfer = spi_bitbang_setup_transfer; status = spi_bitbang_init(&spi_gpio->bitbang); if (status) return status; return devm_spi_register_master(&pdev->dev, spi_master_get(master)); } MODULE_ALIAS("platform:" DRIVER_NAME); static struct platform_driver spi_gpio_driver = { .driver = { .name = DRIVER_NAME, .of_match_table = of_match_ptr(spi_gpio_dt_ids), }, .probe = spi_gpio_probe, }; module_platform_driver(spi_gpio_driver); MODULE_DESCRIPTION("SPI master driver using generic bitbanged GPIO "); MODULE_AUTHOR("David Brownell"); MODULE_LICENSE("GPL");