drivers/gpio/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/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
  51 struct 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
  69 static int gpio_latch_get_direction(struct gpio_chip *gc, unsigned int offset)
  70 {
  71         return GPIO_LINE_DIRECTION_OUT;
  72 }
  73
  74 static 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
  93 static 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
 105 static 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
 116 static 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
 139 static 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
 200 static const struct of_device_id gpio_latch_ids[] = {
 201         {
 202                 .compatible = "gpio-latch",
 203         },
 204         { /* sentinel */ }
 205 };
 206 MODULE_DEVICE_TABLE(of, gpio_latch_ids);
 207
 208 static 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 };
 215 module_platform_driver(gpio_latch_driver);
 216
 217 MODULE_LICENSE("GPL v2");
 218 MODULE_AUTHOR("Sascha Hauer <s.hauer@pengutronix.de>");
 219 MODULE_DESCRIPTION("GPIO latch driver");