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