text: #ifndef _ASM_GENERIC_GPIO_H
  #define _ASM_GENERIC_GPIO_H
  
  #include <linux/kernel.h>
  #include <linux/types.h>
  #include <linux/errno.h>
  
  #ifdef CONFIG_GPIOLIB
  
  #include <linux/compiler.h>
  
  /* Platforms may implement their GPIO interface with library code,
   * at a small performance cost for non-inlined operations and some
   * extra memory (for code and for per-GPIO table entries).
   *
   * While the GPIO programming interface defines valid GPIO numbers
   * to be in the range 0..MAX_INT, this library restricts them to the
   * smaller range 0..ARCH_NR_GPIOS-1.
   */
  
  #ifndef ARCH_NR_GPIOS
  #define ARCH_NR_GPIOS		256
  #endif
  
  static inline int gpio_is_valid(int number)
  {
  	/* only some non-negative numbers are valid */
  	return ((unsigned)number) < ARCH_NR_GPIOS;
  }
  
  struct seq_file;
  struct module;
  
  /**
   * struct gpio_chip - abstract a GPIO controller
   * @label: for diagnostics
   * @dev: optional device providing the GPIOs
   * @owner: helps prevent removal of modules exporting active GPIOs
   * @request: optional hook for chip-specific activation, such as
   *	enabling module power and clock; may sleep
   * @free: optional hook for chip-specific deactivation, such as
   *	disabling module power and clock; may sleep
   * @direction_input: configures signal "offset" as input, or returns error
   * @get: returns value for signal "offset"; for output signals this
   *	returns either the value actually sensed, or zero
   * @direction_output: configures signal "offset" as output, or returns error
   * @set: assigns output value for signal "offset"
   * @to_irq: optional hook supporting non-static gpio_to_irq() mappings;
   *	implementation may not sleep
   * @dbg_show: optional routine to show contents in debugfs; default code
   *	will be used when this is omitted, but custom code can show extra
   *	state (such as pullup/pulldown configuration).
   * @base: identifies the first GPIO number handled by this chip; or, if
   *	negative during registration, requests dynamic ID allocation.
   * @ngpio: the number of GPIOs handled by this controller; the last GPIO
   *	handled is (base + ngpio - 1).
   * @can_sleep: flag must be set iff get()/set() methods sleep, as they
   *	must while accessing GPIO expander chips over I2C or SPI
   * @names: if set, must be an array of strings to use as alternative
   *      names for the GPIOs in this chip. Any entry in the array
   *      may be NULL if there is no alias for the GPIO, however the
   *      array must be @ngpio entries long.
   *
   * A gpio_chip can help platforms abstract various sources of GPIOs so
   * they can all be accessed through a common programing interface.
   * Example sources would be SOC controllers, FPGAs, multifunction
   * chips, dedicated GPIO expanders, and so on.
   *
   * Each chip controls a number of signals, identified in method calls
   * by "offset" values in the range 0..(@ngpio - 1).  When those signals
   * are referenced through calls like gpio_get_value(gpio), the offset
   * is calculated by subtracting @base from the gpio number.
   */
  struct gpio_chip {
  	const char		*label;
  	struct device		*dev;
  	struct module		*owner;
  
  	int			(*request)(struct gpio_chip *chip,
  						unsigned offset);
  	void			(*free)(struct gpio_chip *chip,
  						unsigned offset);
  
  	int			(*direction_input)(struct gpio_chip *chip,
  						unsigned offset);
  	int			(*get)(struct gpio_chip *chip,
  						unsigned offset);
  	int			(*direction_output)(struct gpio_chip *chip,
  						unsigned offset, int value);
  	void			(*set)(struct gpio_chip *chip,
  						unsigned offset, int value);
  
  	int			(*to_irq)(struct gpio_chip *chip,
  						unsigned offset);
  
  	void			(*dbg_show)(struct seq_file *s,
  						struct gpio_chip *chip);
  	int			base;
  	u16			ngpio;
  	char			**names;
  	unsigned		can_sleep:1;
  	unsigned		exported:1;
  };
  
  extern const char *gpiochip_is_requested(struct gpio_chip *chip,
  			unsigned offset);
  extern int __must_check gpiochip_reserve(int start, int ngpio);
  
  /* add/remove chips */
  extern int gpiochip_add(struct gpio_chip *chip);
  extern int __must_check gpiochip_remove(struct gpio_chip *chip);
  
  
  /* Always use the library code for GPIO management calls,
   * or when sleeping may be involved.
   */
  extern int gpio_request(unsigned gpio, const char *label);
  extern void gpio_free(unsigned gpio);
  
  extern int gpio_direction_input(unsigned gpio);
  extern int gpio_direction_output(unsigned gpio, int value);
  
  extern int gpio_get_value_cansleep(unsigned gpio);
  extern void gpio_set_value_cansleep(unsigned gpio, int value);
  
  
  /* A platform's <asm/gpio.h> code may want to inline the I/O calls when
   * the GPIO is constant and refers to some always-present controller,
   * giving direct access to chip registers and tight bitbanging loops.
   */
  extern int __gpio_get_value(unsigned gpio);
  extern void __gpio_set_value(unsigned gpio, int value);
  
  extern int __gpio_cansleep(unsigned gpio);
  
  extern int __gpio_to_irq(unsigned gpio);
  
  #ifdef CONFIG_GPIO_SYSFS
  
  /*
   * A sysfs interface can be exported by individual drivers if they want,
   * but more typically is configured entirely from userspace.
   */
  extern int gpio_export(unsigned gpio, bool direction_may_change);
  extern int gpio_export_link(struct device *dev, const char *name,
  			unsigned gpio);
  extern void gpio_unexport(unsigned gpio);
  
  #endif	/* CONFIG_GPIO_SYSFS */
  
  #else	/* !CONFIG_HAVE_GPIO_LIB */
  
  static inline int gpio_is_valid(int number)
  {
  	/* only non-negative numbers are valid */
  	return number >= 0;
  }
  
  /* platforms that don't directly support access to GPIOs through I2C, SPI,
   * or other blocking infrastructure can use these wrappers.
   */
  
  static inline int gpio_cansleep(unsigned gpio)
  {
  	return 0;
  }
  
  static inline int gpio_get_value_cansleep(unsigned gpio)
  {
  	might_sleep();
  	return gpio_get_value(gpio);
  }
  
  static inline void gpio_set_value_cansleep(unsigned gpio, int value)
  {
  	might_sleep();
  	gpio_set_value(gpio, value);
  }
  
  #endif /* !CONFIG_HAVE_GPIO_LIB */
  
  #ifndef CONFIG_GPIO_SYSFS
  
  /* sysfs support is only available with gpiolib, where it's optional */
  
  static inline int gpio_export(unsigned gpio, bool direction_may_change)
  {
  	return -ENOSYS;
  }
  
  static inline int gpio_export_link(struct device *dev, const char *name,
  				unsigned gpio)
  {
  	return -ENOSYS;
  }
  
  static inline void gpio_unexport(unsigned gpio)
  {
  }
  #endif	/* CONFIG_GPIO_SYSFS */
  
  #endif /* _ASM_GENERIC_GPIO_H */
  