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>
---
drivers/gpio/Kconfig | 6 ++
drivers/gpio/Makefile | 1 +
drivers/gpio/gpio-latch.c | 195 ++++++++++++++++++++++++++++++++++++++
3 files changed, 202 insertions(+)
create mode 100644 drivers/gpio/gpio-latch.c
diff --git a/drivers/gpio/Kconfig b/drivers/gpio/Kconfig
index ab75fe4ed9..dd2b56d256 100644
--- a/drivers/gpio/Kconfig
+++ b/drivers/gpio/Kconfig
@@ -205,6 +205,12 @@ config GPIO_ZYNQ
help
Say yes here to support Xilinx Zynq GPIO controller.
+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.
+
endmenu
endif
diff --git a/drivers/gpio/Makefile b/drivers/gpio/Makefile
index fcb6a232e0..90ab0a8b28 100644
--- a/drivers/gpio/Makefile
+++ b/drivers/gpio/Makefile
@@ -28,3 +28,4 @@ obj-$(CONFIG_GPIO_RASPBERRYPI_EXP) += gpio-raspberrypi-exp.o
obj-$(CONFIG_GPIO_SIFIVE) += gpio-sifive.o
obj-$(CONFIG_GPIO_STARFIVE) += gpio-starfive-vic.o
obj-$(CONFIG_GPIO_ZYNQ) += gpio-zynq.o
+obj-$(CONFIG_GPIO_LATCH) += gpio-latch.o
diff --git a/drivers/gpio/gpio-latch.c b/drivers/gpio/gpio-latch.c
new file mode 100644
index 0000000000..2a89f22401
--- /dev/null
+++ b/drivers/gpio/gpio-latch.c
@@ -0,0 +1,195 @@
+// 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 <common.h>
+#include <errno.h>
+#include <io.h>
+#include <of.h>
+#include <gpio.h>
+#include <init.h>
+#include <of_gpio.h>
+#include <linux/bitmap.h>
+
+struct gpio_latch_priv {
+ struct gpio_chip gc;
+ int *clk_gpios;
+ int *latched_gpios;
+ int n_latched_gpios;
+ unsigned int setup_duration_ns;
+ unsigned int clock_duration_ns;
+ unsigned long *shadow;
+};
+
+static int gpio_latch_get_direction(struct gpio_chip *gc, unsigned int offset)
+{
+ return 0;
+}
+
+static void gpio_latch_set(struct gpio_chip *gc, unsigned int offset, int val)
+{
+ struct gpio_latch_priv *priv = container_of(gc, struct gpio_latch_priv, gc);
+ int latch = offset / priv->n_latched_gpios;
+ int i;
+
+ assign_bit(offset, priv->shadow, val);
+
+ for (i = 0; i < priv->n_latched_gpios; i++)
+ gpio_set_value(priv->latched_gpios[i],
+ test_bit(latch * priv->n_latched_gpios + i, priv->shadow));
+
+ ndelay(priv->setup_duration_ns);
+ gpio_set_value(priv->clk_gpios[latch], 1);
+ ndelay(priv->clock_duration_ns);
+ gpio_set_value(priv->clk_gpios[latch], 0);
+}
+static int gpio_latch_direction_output(struct gpio_chip *gc, unsigned gpio, int val)
+{
+ gpio_latch_set(gc, gpio, val);
+
+ return 0;
+}
+
+#define DURATION_NS_MAX 5000
+
+static struct gpio_ops gpio_latch_gpio_ops = {
+ .direction_output = gpio_latch_direction_output,
+ .set = gpio_latch_set,
+ .get_direction = gpio_latch_get_direction,
+};
+
+static int gpio_latch_probe(struct device_d *dev)
+{
+ struct gpio_latch_priv *priv;
+ int n_latches, i, ret;
+ struct device_node *np = dev->device_node;
+ enum of_gpio_flags flags;
+
+ priv = xzalloc(sizeof(*priv));
+
+ n_latches = of_gpio_named_count(np, "clk-gpios");
+ if (n_latches < 0) {
+ dev_err(dev, "invalid or missing clk-gpios");
+ ret = -EINVAL;
+ goto err_gpio;
+ }
+
+ priv->n_latched_gpios = of_gpio_named_count(np, "latched-gpios");
+ if (priv->n_latched_gpios < 0) {
+ dev_err(dev, "invalid or missing latched-gpios");
+ ret = -EINVAL;
+ goto err_gpio;
+ }
+
+ priv->clk_gpios = xzalloc(sizeof(int) * n_latches);
+ priv->latched_gpios = xzalloc(sizeof(int) * priv->n_latched_gpios);
+
+ for (i = 0; i < n_latches; i++) {
+ priv->clk_gpios[i] = of_get_named_gpio_flags(np, "clk-gpios",
+ i, &flags);
+ ret = gpio_request_one(priv->clk_gpios[i],
+ flags & OF_GPIO_ACTIVE_LOW ? GPIOF_ACTIVE_LOW : 0,
+ dev_name(dev));
+ if (ret) {
+ dev_err(dev, "Cannot request gpio %d: %s\n", priv->clk_gpios[i],
+ strerror(-ret));
+ goto err_gpio;
+ }
+
+ gpio_direction_output(priv->clk_gpios[i], 0);
+ }
+
+ for (i = 0; i < priv->n_latched_gpios; i++) {
+ priv->latched_gpios[i] = of_get_named_gpio_flags(np, "latched-gpios",
+ i, &flags);
+ ret = gpio_request_one(priv->latched_gpios[i],
+ flags & OF_GPIO_ACTIVE_LOW ? GPIOF_ACTIVE_LOW : 0,
+ dev_name(dev));
+ if (ret) {
+ dev_err(dev, "Cannot request gpio %d: %s\n", priv->latched_gpios[i],
+ strerror(-ret));
+ goto err_gpio;
+ }
+ }
+
+ priv->shadow = bitmap_zalloc(n_latches * priv->n_latched_gpios);
+
+ of_property_read_u32(np, "setup-duration-ns", &priv->setup_duration_ns);
+ if (priv->setup_duration_ns > DURATION_NS_MAX) {
+ dev_warn(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(dev, "clock-duration-ns too high, limit to %d\n",
+ DURATION_NS_MAX);
+ priv->clock_duration_ns = DURATION_NS_MAX;
+ }
+
+ priv->gc.ops = &gpio_latch_gpio_ops;
+ priv->gc.ngpio = n_latches * priv->n_latched_gpios;
+ priv->gc.base = -1;
+ priv->gc.dev = dev;
+
+ return gpiochip_add(&priv->gc);
+
+err_gpio:
+ return ret;
+}
+
+static const struct of_device_id gpio_latch_ids[] = {
+ {
+ .compatible = "gpio-latch",
+ }, {
+ /* sentinel */
+ }
+};
+
+static struct driver_d gpio_latch_driver = {
+ .name = "gpio-latch",
+ .probe = gpio_latch_probe,
+ .of_compatible = DRV_OF_COMPAT(gpio_latch_ids),
+};
+device_platform_driver(gpio_latch_driver);
+
+MODULE_LICENSE("GPL v2");
+MODULE_AUTHOR("Sascha Hauer <s.hauer@xxxxxxxxxxxxxx>");
+MODULE_DESCRIPTION("GPIO latch driver");
--
2.30.2
