diff options
Diffstat (limited to 'drivers/spi/spi-gpio.c')
| -rw-r--r-- | drivers/spi/spi-gpio.c | 450 |
1 files changed, 450 insertions, 0 deletions
diff --git a/drivers/spi/spi-gpio.c b/drivers/spi/spi-gpio.c new file mode 100644 index 000000000..3ffdab6ca --- /dev/null +++ b/drivers/spi/spi-gpio.c @@ -0,0 +1,450 @@ +// 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); + + /* + * Only change MOSI to an input if using 3WIRE mode. + * Otherwise, MOSI could be left floating if there is + * no pull resistor connected to the I/O pin, or could + * be left logic high if there is a pull-up. Transmitting + * logic high when only clocking MISO data in can put some + * SPI devices in to a bad state. + */ + if (spi->mode & SPI_3WIRE) { + 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 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 = devm_spi_alloc_master(dev, sizeof(*spi_gpio)); + if (!master) + return -ENOMEM; + + 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, 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"); |