/*
   * Copyright (C) 2015 Texas Instruments Incorporated - http://www.ti.com/
   *	Andrew F. Davis <afd@ti.com>
   *
   * This program is free software; you can redistribute it and/or
   * modify it under the terms of the GNU General Public License version 2 as
   * published by the Free Software Foundation.
   *
   * This program is distributed "as is" WITHOUT ANY WARRANTY of any
   * kind, whether expressed or implied; without even the implied warranty
   * of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   * GNU General Public License version 2 for more details.
   */
  
  #include <linux/delay.h>
  #include <linux/gpio/consumer.h>
  #include <linux/gpio/driver.h>
  #include <linux/module.h>
  #include <linux/mutex.h>
  #include <linux/spi/spi.h>
  
  #define DEFAULT_NGPIO 8
  
  /**
   * struct pisosr_gpio - GPIO driver data
   * @chip: GPIO controller chip
   * @spi: SPI device pointer
   * @buffer: Buffer for device reads
   * @buffer_size: Size of buffer
   * @load_gpio: GPIO pin used to load input into device
   * @lock: Protects read sequences
   */
  struct pisosr_gpio {
  	struct gpio_chip chip;
  	struct spi_device *spi;
  	u8 *buffer;
  	size_t buffer_size;
  	struct gpio_desc *load_gpio;
  	struct mutex lock;
  };
  
  static int pisosr_gpio_refresh(struct pisosr_gpio *gpio)
  {
  	int ret;
  
  	mutex_lock(&gpio->lock);
  
  	if (gpio->load_gpio) {

  		gpiod_set_value_cansleep(gpio->load_gpio, 1);

  		udelay(1); /* registers load time (~10ns) */

  		gpiod_set_value_cansleep(gpio->load_gpio, 0);

  		udelay(1); /* registers recovery time (~5ns) */
  	}
  
  	ret = spi_read(gpio->spi, gpio->buffer, gpio->buffer_size);

  
  	mutex_unlock(&gpio->lock);

  	return ret;

  }
  
  static int pisosr_gpio_get_direction(struct gpio_chip *chip,
  				     unsigned offset)
  {
  	/* This device always input */
  	return 1;
  }
  
  static int pisosr_gpio_direction_input(struct gpio_chip *chip,
  				       unsigned offset)
  {
  	/* This device always input */
  	return 0;
  }
  
  static int pisosr_gpio_direction_output(struct gpio_chip *chip,
  					unsigned offset, int value)
  {
  	/* This device is input only */
  	return -EINVAL;
  }
  
  static int pisosr_gpio_get(struct gpio_chip *chip, unsigned offset)
  {
  	struct pisosr_gpio *gpio = gpiochip_get_data(chip);
  
  	/* Refresh may not always be needed */
  	pisosr_gpio_refresh(gpio);
  
  	return (gpio->buffer[offset / 8] >> (offset % 8)) & 0x1;
  }

  static const struct gpio_chip template_chip = {

  	.label			= "pisosr-gpio",
  	.owner			= THIS_MODULE,
  	.get_direction		= pisosr_gpio_get_direction,
  	.direction_input	= pisosr_gpio_direction_input,
  	.direction_output	= pisosr_gpio_direction_output,
  	.get			= pisosr_gpio_get,
  	.base			= -1,
  	.ngpio			= DEFAULT_NGPIO,
  	.can_sleep		= true,
  };
  
  static int pisosr_gpio_probe(struct spi_device *spi)
  {
  	struct device *dev = &spi->dev;
  	struct pisosr_gpio *gpio;
  	int ret;
  
  	gpio = devm_kzalloc(dev, sizeof(*gpio), GFP_KERNEL);
  	if (!gpio)
  		return -ENOMEM;
  
  	spi_set_drvdata(spi, gpio);
  
  	gpio->chip = template_chip;
  	gpio->chip.parent = dev;
  	of_property_read_u16(dev->of_node, "ngpios", &gpio->chip.ngpio);
  
  	gpio->spi = spi;
  
  	gpio->buffer_size = DIV_ROUND_UP(gpio->chip.ngpio, 8);
  	gpio->buffer = devm_kzalloc(dev, gpio->buffer_size, GFP_KERNEL);
  	if (!gpio->buffer)
  		return -ENOMEM;

  	gpio->load_gpio = devm_gpiod_get_optional(dev, "load", GPIOD_OUT_LOW);

  	if (IS_ERR(gpio->load_gpio)) {
  		ret = PTR_ERR(gpio->load_gpio);

  		if (ret != -EPROBE_DEFER)
  			dev_err(dev, "Unable to allocate load GPIO
  ");
  		return ret;

  	}
  
  	mutex_init(&gpio->lock);
  
  	ret = gpiochip_add_data(&gpio->chip, gpio);
  	if (ret < 0) {
  		dev_err(dev, "Unable to register gpiochip
  ");
  		return ret;
  	}
  
  	return 0;
  }
  
  static int pisosr_gpio_remove(struct spi_device *spi)
  {
  	struct pisosr_gpio *gpio = spi_get_drvdata(spi);
  
  	gpiochip_remove(&gpio->chip);
  
  	mutex_destroy(&gpio->lock);
  
  	return 0;
  }
  
  static const struct spi_device_id pisosr_gpio_id_table[] = {
  	{ "pisosr-gpio", },
  	{ /* sentinel */ }
  };
  MODULE_DEVICE_TABLE(spi, pisosr_gpio_id_table);
  
  static const struct of_device_id pisosr_gpio_of_match_table[] = {
  	{ .compatible = "pisosr-gpio", },
  	{ /* sentinel */ }
  };
  MODULE_DEVICE_TABLE(of, pisosr_gpio_of_match_table);
  
  static struct spi_driver pisosr_gpio_driver = {
  	.driver = {
  		.name = "pisosr-gpio",
  		.of_match_table = pisosr_gpio_of_match_table,
  	},
  	.probe = pisosr_gpio_probe,
  	.remove = pisosr_gpio_remove,
  	.id_table = pisosr_gpio_id_table,
  };
  module_spi_driver(pisosr_gpio_driver);
  
  MODULE_AUTHOR("Andrew F. Davis <afd@ti.com>");
  MODULE_DESCRIPTION("SPI Compatible PISO Shift Register GPIO Driver");
  MODULE_LICENSE("GPL v2");