gpio-latch.c

  1// SPDX-License-Identifier: GPL-2.0
  2/*
  3 * GPIO latch driver
  4 *
  5 *  Copyright (C) 2022 Sascha Hauer <s.hauer@pengutronix.de>
  6 *
  7 * This driver implements a GPIO (or better GPO as there is no input)
  8 * multiplexer based on latches like this:
  9 *
 10 * CLK0 ----------------------.        ,--------.
 11 * CLK1 -------------------.  `--------|>    #0 |
 12 *                         |           |        |
 13 * OUT0 ----------------+--|-----------|D0    Q0|-----|<
 14 * OUT1 --------------+-|--|-----------|D1    Q1|-----|<
 15 * OUT2 ------------+-|-|--|-----------|D2    Q2|-----|<
 16 * OUT3 ----------+-|-|-|--|-----------|D3    Q3|-----|<
 17 * OUT4 --------+-|-|-|-|--|-----------|D4    Q4|-----|<
 18 * OUT5 ------+-|-|-|-|-|--|-----------|D5    Q5|-----|<
 19 * OUT6 ----+-|-|-|-|-|-|--|-----------|D6    Q6|-----|<
 20 * OUT7 --+-|-|-|-|-|-|-|--|-----------|D7    Q7|-----|<
 21 *        | | | | | | | |  |           `--------'
 22 *        | | | | | | | |  |
 23 *        | | | | | | | |  |           ,--------.
 24 *        | | | | | | | |  `-----------|>    #1 |
 25 *        | | | | | | | |              |        |
 26 *        | | | | | | | `--------------|D0    Q0|-----|<
 27 *        | | | | | | `----------------|D1    Q1|-----|<
 28 *        | | | | | `------------------|D2    Q2|-----|<
 29 *        | | | | `--------------------|D3    Q3|-----|<
 30 *        | | | `----------------------|D4    Q4|-----|<
 31 *        | | `------------------------|D5    Q5|-----|<
 32 *        | `--------------------------|D6    Q6|-----|<
 33 *        `----------------------------|D7    Q7|-----|<
 34 *                                     `--------'
 35 *
 36 * The above is just an example. The actual number of number of latches and
 37 * the number of inputs per latch is derived from the number of GPIOs given
 38 * in the corresponding device tree properties.
 39 */
 40
 41#include <linux/cleanup.h>
 42#include <linux/err.h>
 43#include <linux/gpio/consumer.h>
 44#include <linux/gpio/driver.h>
 45#include <linux/module.h>
 46#include <linux/mod_devicetable.h>
 47#include <linux/platform_device.h>
 48#include <linux/property.h>
 49#include <linux/delay.h>
 50
 51struct gpio_latch_priv {
 52	struct gpio_chip gc;
 53	struct gpio_descs *clk_gpios;
 54	struct gpio_descs *latched_gpios;
 55	int n_latched_gpios;
 56	unsigned int setup_duration_ns;
 57	unsigned int clock_duration_ns;
 58	unsigned long *shadow;
 59	/*
 60	 * Depending on whether any of the underlying GPIOs may sleep we either
 61	 * use a mutex or a spinlock to protect our shadow map.
 62	 */
 63	union {
 64		struct mutex mutex; /* protects @shadow */
 65		spinlock_t spinlock; /* protects @shadow */
 66	};
 67};
 68
 69static int gpio_latch_get_direction(struct gpio_chip *gc, unsigned int offset)
 70{
 71	return GPIO_LINE_DIRECTION_OUT;
 72}
 73
 74static int gpio_latch_set_unlocked(struct gpio_latch_priv *priv,
 75				   int (*set)(struct gpio_desc *desc, int value),
 76				   unsigned int offset, bool val)
 77{
 78	int latch = offset / priv->n_latched_gpios, i, ret;
 79
 80	assign_bit(offset, priv->shadow, val);
 81
 82	for (i = 0; i < priv->n_latched_gpios; i++) {
 83		ret = set(priv->latched_gpios->desc[i],
 84			  test_bit(latch * priv->n_latched_gpios + i,
 85				   priv->shadow));
 86		if (ret)
 87			return ret;
 88	}
 89
 90	ndelay(priv->setup_duration_ns);
 91	set(priv->clk_gpios->desc[latch], 1);
 92	ndelay(priv->clock_duration_ns);
 93	set(priv->clk_gpios->desc[latch], 0);
 94
 95	return 0;
 96}
 97
 98static int gpio_latch_set(struct gpio_chip *gc, unsigned int offset, int val)
 99{
100	struct gpio_latch_priv *priv = gpiochip_get_data(gc);
101
102	guard(spinlock_irqsave)(&priv->spinlock);
103
104	return gpio_latch_set_unlocked(priv, gpiod_set_value, offset, val);
105}
106
107static int gpio_latch_set_can_sleep(struct gpio_chip *gc, unsigned int offset, int val)
108{
109	struct gpio_latch_priv *priv = gpiochip_get_data(gc);
110
111	guard(mutex)(&priv->mutex);
112
113	return gpio_latch_set_unlocked(priv, gpiod_set_value_cansleep, offset, val);
114}
115
116static bool gpio_latch_can_sleep(struct gpio_latch_priv *priv, unsigned int n_latches)
117{
118	int i;
119
120	for (i = 0; i < n_latches; i++)
121		if (gpiod_cansleep(priv->clk_gpios->desc[i]))
122			return true;
123
124	for (i = 0; i < priv->n_latched_gpios; i++)
125		if (gpiod_cansleep(priv->latched_gpios->desc[i]))
126			return true;
127
128	return false;
129}
130
131/*
132 * Some value which is still acceptable to delay in atomic context.
133 * If we need to go higher we might have to switch to usleep_range(),
134 * but that cannot ne used in atomic context and the driver would have
135 * to be adjusted to support that.
136 */
137#define DURATION_NS_MAX 5000
138
139static int gpio_latch_probe(struct platform_device *pdev)
140{
141	struct device *dev = &pdev->dev;
142	struct gpio_latch_priv *priv;
143	unsigned int n_latches;
144
145	priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
146	if (!priv)
147		return -ENOMEM;
148
149	priv->clk_gpios = devm_gpiod_get_array(dev, "clk", GPIOD_OUT_LOW);
150	if (IS_ERR(priv->clk_gpios))
151		return PTR_ERR(priv->clk_gpios);
152
153	priv->latched_gpios = devm_gpiod_get_array(dev, "latched", GPIOD_OUT_LOW);
154	if (IS_ERR(priv->latched_gpios))
155		return PTR_ERR(priv->latched_gpios);
156
157	n_latches = priv->clk_gpios->ndescs;
158	priv->n_latched_gpios = priv->latched_gpios->ndescs;
159
160	priv->shadow = devm_bitmap_zalloc(dev, n_latches * priv->n_latched_gpios,
161					  GFP_KERNEL);
162	if (!priv->shadow)
163		return -ENOMEM;
164
165	if (gpio_latch_can_sleep(priv, n_latches)) {
166		priv->gc.can_sleep = true;
167		priv->gc.set = gpio_latch_set_can_sleep;
168		mutex_init(&priv->mutex);
169	} else {
170		priv->gc.can_sleep = false;
171		priv->gc.set = gpio_latch_set;
172		spin_lock_init(&priv->spinlock);
173	}
174
175	device_property_read_u32(dev, "setup-duration-ns",
176				 &priv->setup_duration_ns);
177	if (priv->setup_duration_ns > DURATION_NS_MAX) {
178		dev_warn(dev, "setup-duration-ns too high, limit to %d\n",
179			 DURATION_NS_MAX);
180		priv->setup_duration_ns = DURATION_NS_MAX;
181	}
182
183	device_property_read_u32(dev, "clock-duration-ns",
184				 &priv->clock_duration_ns);
185	if (priv->clock_duration_ns > DURATION_NS_MAX) {
186		dev_warn(dev, "clock-duration-ns too high, limit to %d\n",
187			 DURATION_NS_MAX);
188		priv->clock_duration_ns = DURATION_NS_MAX;
189	}
190
191	priv->gc.get_direction = gpio_latch_get_direction;
192	priv->gc.ngpio = n_latches * priv->n_latched_gpios;
193	priv->gc.owner = THIS_MODULE;
194	priv->gc.base = -1;
195	priv->gc.parent = dev;
196
197	platform_set_drvdata(pdev, priv);
198
199	return devm_gpiochip_add_data(dev, &priv->gc, priv);
200}
201
202static const struct of_device_id gpio_latch_ids[] = {
203	{
204		.compatible = "gpio-latch",
205	},
206	{ /* sentinel */ }
207};
208MODULE_DEVICE_TABLE(of, gpio_latch_ids);
209
210static struct platform_driver gpio_latch_driver = {
211	.driver	= {
212		.name		= "gpio-latch",
213		.of_match_table	= gpio_latch_ids,
214	},
215	.probe	= gpio_latch_probe,
216};
217module_platform_driver(gpio_latch_driver);
218
219MODULE_LICENSE("GPL v2");
220MODULE_AUTHOR("Sascha Hauer <s.hauer@pengutronix.de>");
221MODULE_DESCRIPTION("GPIO latch driver");