linux-imx

/*

 * SPI master driver using generic bitbanged GPIO

 *

 * Copyright (C) 2006,2008 David Brownell

 * Copyright (C) 2017 Linus Walleij

 *

 * This program is free software; you can redistribute it and/or modify

 * it under the terms of the GNU General Public License as published by

 * the Free Software Foundation; either version 2 of the License, or

 * (at your option) any later version.

 *

 * This program is distributed in the hope that it will be useful,

 * but WITHOUT ANY WARRANTY; without even the implied warranty of

 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

 * GNU General Public License for more details.

 */

#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->controller_data ... holds chipselect GPIO

 *

 * spi->master->dev.driver_data ... points to spi_gpio->bitbang

 */

​

struct spi_gpio {

    struct spi_bitbang      bitbang;

    struct spi_gpio_platform_data   pdata;

    struct platform_device      *pdev;

    struct gpio_desc        *sck;

    struct gpio_desc        *miso;

    struct gpio_desc        *mosi;

    struct gpio_desc        **cs_gpios;

    bool                has_cs;

};

​

/*----------------------------------------------------------------------*/

​

/*

 * 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.