This driver implements a GPIO multiplexer based on latches connected to
other GPIOs. A set of data GPIOs is connected to the data input of
multiple latches. The clock input of each latch is driven by another
set of GPIOs. With two 8-bit latches 10 GPIOs can be multiplexed into
16 GPIOs. GPOs might be a better term as in fact the multiplexed pins
are output only.
Signed-off-by: Sascha Hauer <s.hauer@xxxxxxxxxxxxxx>
---
Notes:
Changes since v2:
- Fix inconsistent licensing
- document locks
- use regular bit operations
- include linux/mod_devicetable.h rather than linux/of_device.h
- Put spinlock and mutex into a union to make clear that only one of them is used
- rename __gpio_latch_set to gpio_latch_set_unlocked
Changes since v1:
- Use gpiod_set_value_cansleep when the underlying GPIOs might sleep
- Move MODULE_DEVICE_TABLE near to the end
drivers/gpio/Kconfig | 6 ++
drivers/gpio/Makefile | 1 +
drivers/gpio/gpio-latch.c | 192 ++++++++++++++++++++++++++++++++++++++
3 files changed, 199 insertions(+)
create mode 100644 drivers/gpio/gpio-latch.c
diff --git a/drivers/gpio/Kconfig b/drivers/gpio/Kconfig
index 0642f579196f2..e4603810ec910 100644
--- a/drivers/gpio/Kconfig
+++ b/drivers/gpio/Kconfig
@@ -1690,6 +1690,12 @@ config GPIO_AGGREGATOR
industrial control context, to be operated from userspace using
the GPIO chardev interface.
+config GPIO_LATCH
+ tristate "GPIO latch driver"
+ help
+ Say yes here to enable a driver for GPIO multiplexers based on latches
+ connected to other GPIOs.
+
config GPIO_MOCKUP
tristate "GPIO Testing Driver"
select IRQ_SIM
diff --git a/drivers/gpio/Makefile b/drivers/gpio/Makefile
index a0985d30f51bb..310fa08decc69 100644
--- a/drivers/gpio/Makefile
+++ b/drivers/gpio/Makefile
@@ -75,6 +75,7 @@ obj-$(CONFIG_GPIO_IT87) += gpio-it87.o
obj-$(CONFIG_GPIO_IXP4XX) += gpio-ixp4xx.o
obj-$(CONFIG_GPIO_JANZ_TTL) += gpio-janz-ttl.o
obj-$(CONFIG_GPIO_KEMPLD) += gpio-kempld.o
+obj-$(CONFIG_GPIO_LATCH) += gpio-latch.o
obj-$(CONFIG_GPIO_LOGICVC) += gpio-logicvc.o
obj-$(CONFIG_GPIO_LOONGSON1) += gpio-loongson1.o
obj-$(CONFIG_GPIO_LOONGSON) += gpio-loongson.o
diff --git a/drivers/gpio/gpio-latch.c b/drivers/gpio/gpio-latch.c
new file mode 100644
index 0000000000000..4134cba1c88a8
--- /dev/null
+++ b/drivers/gpio/gpio-latch.c
@@ -0,0 +1,192 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * GPIO latch driver
+ *
+ * Copyright (C) 2022 Sascha Hauer <s.hauer@xxxxxxxxxxxxxx>
+ *
+ * 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 "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 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));
+
+ set(priv->clk_gpios->desc[latch], 1);
+ 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;
+}
+
+static int gpio_latch_probe(struct platform_device *pdev)
+{
+ struct gpio_latch_priv *priv;
+ unsigned int n_latches;
+
+ 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);
+ }
+
+ 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 <s.hauer@xxxxxxxxxxxxxx>");
+MODULE_DESCRIPTION("GPIO latch driver");
--
2.30.2
