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459 lines
13 KiB
C
459 lines
13 KiB
C
/*
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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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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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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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if (IS_ERR(spi_gpio->sck))
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return PTR_ERR(spi_gpio->sck);
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return 0;
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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 void spi_gpio_put(void *data)
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{
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spi_master_put(data);
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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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const struct of_device_id *of_id;
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of_id = of_match_device(spi_gpio_dt_ids, &pdev->dev);
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master = spi_alloc_master(dev, sizeof(*spi_gpio));
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if (!master)
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return -ENOMEM;
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status = devm_add_action_or_reset(&pdev->dev, spi_gpio_put, master);
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if (status)
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return status;
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if (of_id)
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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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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, spi_master_get(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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