/*
   * Copyright (C) 2013 TangoTec Ltd.
   * Author: Baruch Siach <baruch@tkos.co.il>
   *
   * 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.
   *
   * Driver for the Xtensa LX4 GPIO32 Option
   *
   * Documentation: Xtensa LX4 Microprocessor Data Book, Section 2.22
   *
   * GPIO32 is a standard optional extension to the Xtensa architecture core that
   * provides preconfigured output and input ports for intra SoC signaling. The
   * GPIO32 option is implemented as 32bit Tensilica Instruction Extension (TIE)
   * output state called EXPSTATE, and 32bit input wire called IMPWIRE. This
   * driver treats input and output states as two distinct devices.
   *
   * Access to GPIO32 specific instructions is controlled by the CPENABLE
   * (Coprocessor Enable Bits) register. By default Xtensa Linux startup code
   * disables access to all coprocessors. This driver sets the CPENABLE bit
   * corresponding to GPIO32 before any GPIO32 specific instruction, and restores
   * CPENABLE state after that.
   *
   * This driver is currently incompatible with SMP. The GPIO32 extension is not
   * guaranteed to be available in all cores. Moreover, each core controls a
   * different set of IO wires. A theoretical SMP aware version of this driver
   * would need to have a per core workqueue to do the actual GPIO manipulation.
   */
  
  #include <linux/err.h>
  #include <linux/module.h>
  #include <linux/gpio.h>
  #include <linux/bitops.h>
  #include <linux/platform_device.h>
  
  #include <asm/coprocessor.h> /* CPENABLE read/write macros */
  
  #ifndef XCHAL_CP_ID_XTIOP
  #error GPIO32 option is not enabled for your xtensa core variant
  #endif
  
  #if XCHAL_HAVE_CP
  
  static inline unsigned long enable_cp(unsigned long *cpenable)
  {
  	unsigned long flags;
  
  	local_irq_save(flags);
  	RSR_CPENABLE(*cpenable);
  	WSR_CPENABLE(*cpenable | BIT(XCHAL_CP_ID_XTIOP));
  
  	return flags;
  }
  
  static inline void disable_cp(unsigned long flags, unsigned long cpenable)
  {
  	WSR_CPENABLE(cpenable);
  	local_irq_restore(flags);
  }
  
  #else
  
  static inline unsigned long enable_cp(unsigned long *cpenable)
  {
  	*cpenable = 0; /* avoid uninitialized value warning */
  	return 0;
  }
  
  static inline void disable_cp(unsigned long flags, unsigned long cpenable)
  {
  }
  
  #endif /* XCHAL_HAVE_CP */
  
  static int xtensa_impwire_get_direction(struct gpio_chip *gc, unsigned offset)
  {
  	return 1; /* input only */
  }
  
  static int xtensa_impwire_get_value(struct gpio_chip *gc, unsigned offset)
  {
  	unsigned long flags, saved_cpenable;
  	u32 impwire;
  
  	flags = enable_cp(&saved_cpenable);
  	__asm__ __volatile__("read_impwire %0" : "=a" (impwire));
  	disable_cp(flags, saved_cpenable);
  
  	return !!(impwire & BIT(offset));
  }
  
  static void xtensa_impwire_set_value(struct gpio_chip *gc, unsigned offset,
  				    int value)
  {
  	BUG(); /* output only; should never be called */
  }
  
  static int xtensa_expstate_get_direction(struct gpio_chip *gc, unsigned offset)
  {
  	return 0; /* output only */
  }
  
  static int xtensa_expstate_get_value(struct gpio_chip *gc, unsigned offset)
  {
  	unsigned long flags, saved_cpenable;
  	u32 expstate;
  
  	flags = enable_cp(&saved_cpenable);
  	__asm__ __volatile__("rur.expstate %0" : "=a" (expstate));
  	disable_cp(flags, saved_cpenable);
  
  	return !!(expstate & BIT(offset));
  }
  
  static void xtensa_expstate_set_value(struct gpio_chip *gc, unsigned offset,
  				     int value)
  {
  	unsigned long flags, saved_cpenable;
  	u32 mask = BIT(offset);
  	u32 val = value ? BIT(offset) : 0;
  
  	flags = enable_cp(&saved_cpenable);
  	__asm__ __volatile__("wrmsk_expstate %0, %1"
  			     :: "a" (val), "a" (mask));
  	disable_cp(flags, saved_cpenable);
  }
  
  static struct gpio_chip impwire_chip = {
  	.label		= "impwire",
  	.base		= -1,
  	.ngpio		= 32,
  	.get_direction	= xtensa_impwire_get_direction,
  	.get		= xtensa_impwire_get_value,
  	.set		= xtensa_impwire_set_value,
  };
  
  static struct gpio_chip expstate_chip = {
  	.label		= "expstate",
  	.base		= -1,
  	.ngpio		= 32,
  	.get_direction	= xtensa_expstate_get_direction,
  	.get		= xtensa_expstate_get_value,
  	.set		= xtensa_expstate_set_value,
  };
  
  static int xtensa_gpio_probe(struct platform_device *pdev)
  {
  	int ret;
  
  	ret = gpiochip_add(&impwire_chip);
  	if (ret)
  		return ret;
  	return gpiochip_add(&expstate_chip);
  }
  
  static struct platform_driver xtensa_gpio_driver = {
  	.driver		= {
  		.name		= "xtensa-gpio",
  		.owner		= THIS_MODULE,
  	},
  	.probe		= xtensa_gpio_probe,
  };
  
  static int __init xtensa_gpio_init(void)
  {
  	struct platform_device *pdev;
  
  	pdev = platform_device_register_simple("xtensa-gpio", 0, NULL, 0);
  	if (IS_ERR(pdev))
  		return PTR_ERR(pdev);
  
  	return platform_driver_register(&xtensa_gpio_driver);
  }
  device_initcall(xtensa_gpio_init);
  
  MODULE_AUTHOR("Baruch Siach <baruch@tkos.co.il>");
  MODULE_DESCRIPTION("Xtensa LX4 GPIO32 driver");
  MODULE_LICENSE("GPL");