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/err.h>
42#include <linux/gpio/consumer.h>
43#include <linux/gpio/driver.h>
44#include <linux/module.h>
45#include <linux/mod_devicetable.h>
46#include <linux/platform_device.h>
47#include <linux/delay.h>
48
49#include "gpiolib.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 void gpio_latch_set_unlocked(struct gpio_latch_priv *priv,
75				    void (*set)(struct gpio_desc *desc, int value),
76				    unsigned int offset, bool val)
77{
78	int latch = offset / priv->n_latched_gpios;
79	int i;
80
81	assign_bit(offset, priv->shadow, val);
82
83	for (i = 0; i < priv->n_latched_gpios; i++)
84		set(priv->latched_gpios->desc[i],
85		    test_bit(latch * priv->n_latched_gpios + i, priv->shadow));
86
87	ndelay(priv->setup_duration_ns);
88	set(priv->clk_gpios->desc[latch], 1);
89	ndelay(priv->clock_duration_ns);
90	set(priv->clk_gpios->desc[latch], 0);
91}
92
93static void gpio_latch_set(struct gpio_chip *gc, unsigned int offset, int val)
94{
95	struct gpio_latch_priv *priv = gpiochip_get_data(gc);
96	unsigned long flags;
97
98	spin_lock_irqsave(&priv->spinlock, flags);
99
100	gpio_latch_set_unlocked(priv, gpiod_set_value, offset, val);
101
102	spin_unlock_irqrestore(&priv->spinlock, flags);
103}
104
105static void gpio_latch_set_can_sleep(struct gpio_chip *gc, unsigned int offset, int val)
106{
107	struct gpio_latch_priv *priv = gpiochip_get_data(gc);
108
109	mutex_lock(&priv->mutex);
110
111	gpio_latch_set_unlocked(priv, gpiod_set_value_cansleep, offset, val);
112
113	mutex_unlock(&priv->mutex);
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 gpio_latch_priv *priv;
142	unsigned int n_latches;
143	struct device_node *np = pdev->dev.of_node;
144
145	priv = devm_kzalloc(&pdev->dev, sizeof(*priv), GFP_KERNEL);
146	if (!priv)
147		return -ENOMEM;
148
149	priv->clk_gpios = devm_gpiod_get_array(&pdev->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(&pdev->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(&pdev->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	of_property_read_u32(np, "setup-duration-ns", &priv->setup_duration_ns);
176	if (priv->setup_duration_ns > DURATION_NS_MAX) {
177		dev_warn(&pdev->dev, "setup-duration-ns too high, limit to %d\n",
178			 DURATION_NS_MAX);
179		priv->setup_duration_ns = DURATION_NS_MAX;
180	}
181
182	of_property_read_u32(np, "clock-duration-ns", &priv->clock_duration_ns);
183	if (priv->clock_duration_ns > DURATION_NS_MAX) {
184		dev_warn(&pdev->dev, "clock-duration-ns too high, limit to %d\n",
185			 DURATION_NS_MAX);
186		priv->clock_duration_ns = DURATION_NS_MAX;
187	}
188
189	priv->gc.get_direction = gpio_latch_get_direction;
190	priv->gc.ngpio = n_latches * priv->n_latched_gpios;
191	priv->gc.owner = THIS_MODULE;
192	priv->gc.base = -1;
193	priv->gc.parent = &pdev->dev;
194
195	platform_set_drvdata(pdev, priv);
196
197	return devm_gpiochip_add_data(&pdev->dev, &priv->gc, priv);
198}
199
200static const struct of_device_id gpio_latch_ids[] = {
201	{
202		.compatible = "gpio-latch",
203	},
204	{ /* sentinel */ }
205};
206MODULE_DEVICE_TABLE(of, gpio_latch_ids);
207
208static struct platform_driver gpio_latch_driver = {
209	.driver	= {
210		.name		= "gpio-latch",
211		.of_match_table	= gpio_latch_ids,
212	},
213	.probe	= gpio_latch_probe,
214};
215module_platform_driver(gpio_latch_driver);
216
217MODULE_LICENSE("GPL v2");
218MODULE_AUTHOR("Sascha Hauer <s.hauer@pengutronix.de>");
219MODULE_DESCRIPTION("GPIO latch driver");
220