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/*
* 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
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);
}
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");
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