// SPDX-License-Identifier: GPL-2.0
/*
* GPIO latch driver
*
* Copyright (C) 2022 Sascha Hauer <[email protected]>
*
* This driver implements a GPIO (or better GPO as there is no input)
* multiplexer based on latches like this:
*
* CLK0 ----------------------. ,--------.
* CLK1 -------------------. `--------|> #0 |
* | | |
* OUT0 ----------------+--|-----------|D0 Q0|-----|<
* OUT1 --------------+-|--|-----------|D1 Q1|-----|<
* OUT2 ------------+-|-|--|-----------|D2 Q2|-----|<
* OUT3 ----------+-|-|-|--|-----------|D3 Q3|-----|<
* OUT4 --------+-|-|-|-|--|-----------|D4 Q4|-----|<
* OUT5 ------+-|-|-|-|-|--|-----------|D5 Q5|-----|<
* OUT6 ----+-|-|-|-|-|-|--|-----------|D6 Q6|-----|<
* OUT7 --+-|-|-|-|-|-|-|--|-----------|D7 Q7|-----|<
* | | | | | | | | | `--------'
* | | | | | | | | |
* | | | | | | | | | ,--------.
* | | | | | | | | `-----------|> #1 |
* | | | | | | | | | |
* | | | | | | | `--------------|D0 Q0|-----|<
* | | | | | | `----------------|D1 Q1|-----|<
* | | | | | `------------------|D2 Q2|-----|<
* | | | | `--------------------|D3 Q3|-----|<
* | | | `----------------------|D4 Q4|-----|<
* | | `------------------------|D5 Q5|-----|<
* | `--------------------------|D6 Q6|-----|<
* `----------------------------|D7 Q7|-----|<
* `--------'
*
* The above is just an example. The actual number of number of latches and
* the number of inputs per latch is derived from the number of GPIOs given
* in the corresponding device tree properties.
*/
#include <linux/err.h>
#include <linux/gpio/consumer.h>
#include <linux/gpio/driver.h>
#include <linux/module.h>
#include <linux/mod_devicetable.h>
#include <linux/platform_device.h>
#include <linux/delay.h>
#include "gpiolib.h"
struct gpio_latch_priv {
struct gpio_chip gc;
struct gpio_descs *clk_gpios;
struct gpio_descs *latched_gpios;
int n_latched_gpios;
unsigned int setup_duration_ns;
unsigned int clock_duration_ns;
unsigned long *shadow;
/*
* Depending on whether any of the underlying GPIOs may sleep we either
* use a mutex or a spinlock to protect our shadow map.
*/
union {
struct mutex mutex; /* protects @shadow */
spinlock_t spinlock; /* protects @shadow */
};
};
static int gpio_latch_get_direction(struct gpio_chip *gc, unsigned int offset)
{
return GPIO_LINE_DIRECTION_OUT;
}
static void gpio_latch_set_unlocked(struct gpio_latch_priv *priv,
void (*set)(struct gpio_desc *desc, int value),
unsigned int offset, bool val)
{
int latch = offset / priv->n_latched_gpios;
int i;
assign_bit(offset, priv->shadow, val);
for (i = 0; i < priv->n_latched_gpios; i++)
set(priv->latched_gpios->desc[i],
test_bit(latch * priv->n_latched_gpios + i, priv->shadow));
ndelay(priv->setup_duration_ns);
set(priv->clk_gpios->desc[latch], 1);
ndelay(priv->clock_duration_ns);
set(priv->clk_gpios->desc[latch], 0);
}
static void gpio_latch_set(struct gpio_chip *gc, unsigned int offset, int val)
{
struct gpio_latch_priv *priv = gpiochip_get_data(gc);
unsigned long flags;
spin_lock_irqsave(&priv->spinlock, flags);
gpio_latch_set_unlocked(priv, gpiod_set_value, offset, val);
spin_unlock_irqrestore(&priv->spinlock, flags);
}
static void gpio_latch_set_can_sleep(struct gpio_chip *gc, unsigned int offset, int val)
{
struct gpio_latch_priv *priv = gpiochip_get_data(gc);
mutex_lock(&priv->mutex);
gpio_latch_set_unlocked(priv, gpiod_set_value_cansleep, offset, val);
mutex_unlock(&priv->mutex);
}
static bool gpio_latch_can_sleep(struct gpio_latch_priv *priv, unsigned int n_latches)
{
int i;
for (i = 0; i < n_latches; i++)
if (gpiod_cansleep(priv->clk_gpios->desc[i]))
return true;
for (i = 0; i < priv->n_latched_gpios; i++)
if (gpiod_cansleep(priv->latched_gpios->desc[i]))
return true;
return false;
}
/*
* Some value which is still acceptable to delay in atomic context.
* If we need to go higher we might have to switch to usleep_range(),
* but that cannot ne used in atomic context and the driver would have
* to be adjusted to support that.
*/
#define DURATION_NS_MAX 5000
static int gpio_latch_probe(struct platform_device *pdev)
{
struct gpio_latch_priv *priv;
unsigned int n_latches;
struct device_node *np = pdev->dev.of_node;
priv = devm_kzalloc(&pdev->dev, sizeof(*priv), GFP_KERNEL);
if (!priv)
return -ENOMEM;
priv->clk_gpios = devm_gpiod_get_array(&pdev->dev, "clk", GPIOD_OUT_LOW);
if (IS_ERR(priv->clk_gpios))
return PTR_ERR(priv->clk_gpios);
priv->latched_gpios = devm_gpiod_get_array(&pdev->dev, "latched", GPIOD_OUT_LOW);
if (IS_ERR(priv->latched_gpios))
return PTR_ERR(priv->latched_gpios);
n_latches = priv->clk_gpios->ndescs;
priv->n_latched_gpios = priv->latched_gpios->ndescs;
priv->shadow = devm_bitmap_zalloc(&pdev->dev, n_latches * priv->n_latched_gpios,
GFP_KERNEL);
if (!priv->shadow)
return -ENOMEM;
if (gpio_latch_can_sleep(priv, n_latches)) {
priv->gc.can_sleep = true;
priv->gc.set = gpio_latch_set_can_sleep;
mutex_init(&priv->mutex);
} else {
priv->gc.can_sleep = false;
priv->gc.set = gpio_latch_set;
spin_lock_init(&priv->spinlock);
}
of_property_read_u32(np, "setup-duration-ns", &priv->setup_duration_ns);
if (priv->setup_duration_ns > DURATION_NS_MAX) {
dev_warn(&pdev->dev, "setup-duration-ns too high, limit to %d\n",
DURATION_NS_MAX);
priv->setup_duration_ns = DURATION_NS_MAX;
}
of_property_read_u32(np, "clock-duration-ns", &priv->clock_duration_ns);
if (priv->clock_duration_ns > DURATION_NS_MAX) {
dev_warn(&pdev->dev, "clock-duration-ns too high, limit to %d\n",
DURATION_NS_MAX);
priv->clock_duration_ns = DURATION_NS_MAX;
}
priv->gc.get_direction = gpio_latch_get_direction;
priv->gc.ngpio = n_latches * priv->n_latched_gpios;
priv->gc.owner = THIS_MODULE;
priv->gc.base = -1;
priv->gc.parent = &pdev->dev;
platform_set_drvdata(pdev, priv);
return devm_gpiochip_add_data(&pdev->dev, &priv->gc, priv);
}
static const struct of_device_id gpio_latch_ids[] = {
{
.compatible = "gpio-latch",
},
{ /* sentinel */ }
};
MODULE_DEVICE_TABLE(of, gpio_latch_ids);
static struct platform_driver gpio_latch_driver = {
.driver = {
.name = "gpio-latch",
.of_match_table = gpio_latch_ids,
},
.probe = gpio_latch_probe,
};
module_platform_driver(gpio_latch_driver);
MODULE_LICENSE("GPL v2");
MODULE_AUTHOR("Sascha Hauer <[email protected]>");
MODULE_DESCRIPTION("GPIO latch driver");
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