Selected GPIOs (defined as child nodes in DT) may be exported as
symlinks to user space (using gpiod_export_link())
The advantages of this are:
* Userspace no longer needs to know the GPIO number (which may
vary with other hardware and with kernel version due to dynamic
allocation)
* Userspace can be prevented from changing the direction if that
does not make sense from a hardware perspective.
Signed-off-by: Martin Fuzzey <mfuzzey@xxxxxxxxxxx>
---
drivers/gpio/Kconfig | 9 ++
drivers/gpio/Makefile | 1
drivers/gpio/gpio-exporter.c | 171 ++++++++++++++++++++++++++++++++++++++++++
3 files changed, 181 insertions(+)
create mode 100644 drivers/gpio/gpio-exporter.c
diff --git a/drivers/gpio/Kconfig b/drivers/gpio/Kconfig
index 633ec21..682fce2 100644
--- a/drivers/gpio/Kconfig
+++ b/drivers/gpio/Kconfig
@@ -110,6 +110,15 @@ config GPIO_DA9055
config GPIO_MAX730X
tristate
+config GPIO_EXPORTER
+ tristate "Userspace exporter driver"
+ depends on OF_GPIO && GPIO_SYSFS
+ help
+ This enables a GPIO consumer which exports some GPIOs to userspace.
+ The GPIOs to be exported are defined in the device tree.
+ The exported GPIOs are represented as symbolic links in sysfs,
+ relieving usespace of the burden of knowing the GPIO number to export
+
comment "Memory mapped GPIO drivers:"
config GPIO_74XX_MMIO
diff --git a/drivers/gpio/Makefile b/drivers/gpio/Makefile
index 81755f1..bb665c5 100644
--- a/drivers/gpio/Makefile
+++ b/drivers/gpio/Makefile
@@ -10,6 +10,7 @@ obj-$(CONFIG_GPIO_SYSFS) += gpiolib-sysfs.o
obj-$(CONFIG_GPIO_ACPI) += gpiolib-acpi.o
# Device drivers. Generally keep list sorted alphabetically
+obj-$(CONFIG_GPIO_EXPORTER) += gpio-exporter.o
obj-$(CONFIG_GPIO_GENERIC) += gpio-generic.o
obj-$(CONFIG_GPIO_74X164) += gpio-74x164.o
diff --git a/drivers/gpio/gpio-exporter.c b/drivers/gpio/gpio-exporter.c
new file mode 100644
index 0000000..72cdcf0
--- /dev/null
+++ b/drivers/gpio/gpio-exporter.c
@@ -0,0 +1,171 @@
+/*
+ * A driver that allows some gpios to be exported to userspace
+ * using friendly names.
+ *
+ * This allows the gpios to be exported to be configured in the device tree
+ * and frees userspace from having to know unstable gpio numbers.
+ *
+ * Copyright 2015 Parkeon
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation; either version 2 of the
+ * License, or (at your option) any later version.
+ *
+ */
+
+#include <linux/device.h>
+#include <linux/err.h>
+#include <linux/gpio/consumer.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/of_device.h>
+#include <linux/platform_device.h>
+
+
+struct gpio_exporter_gpio {
+ const char *name;
+ struct gpio_desc *desc;
+};
+
+struct gpio_exporter_data {
+ struct device *dev;
+ int num_gpios;
+ struct gpio_exporter_gpio *gpios;
+};
+
+static int gpio_exporter_do_one(struct gpio_exporter_data *data,
+ struct fwnode_handle *child)
+{
+ struct device_node *np = of_node(child);
+ const char *name = np->name;
+ const char *config;
+ struct gpio_desc *desc;
+ int ret;
+
+ desc = devm_get_gpiod_from_child(data->dev, child);
+ if (IS_ERR(desc)) {
+ ret = PTR_ERR(desc);
+ goto failed_get;
+ }
+
+ if (of_property_read_bool(np, "output")) {
+ u32 state = 0;
+
+ of_property_read_u32(np, "initial-state", &state);
+ ret = gpiod_direction_output(desc, state);
+ } else {
+ ret = gpiod_direction_input(desc);
+ }
+ if (ret)
+ goto failed_setdir;
+
+ ret = gpiod_export(desc,
+ of_property_read_bool(np, "allow-direction-change"));
+ if (ret)
+ goto failed_export;
+
+ ret = gpiod_export_link(data->dev, name, desc);
+ if (ret)
+ goto failed_link;
+
+ data->gpios[data->num_gpios].name = name;
+ data->gpios[data->num_gpios].desc = desc;
+ data->num_gpios++;
+
+ dev_info(data->dev,
+ "Exported gpio%d as '%s'\n", desc_to_gpio(desc), name);
+
+ return 0;
+
+failed_link:
+ gpiod_unexport(desc);
+
+failed_export:
+failed_setdir:
+failed_get:
+ dev_err(data->dev, "Failed to export gpio '%s': %d\n", name, ret);
+
+ return ret;
+}
+
+static void gpio_exporter_cleanup(struct gpio_exporter_data *data)
+{
+ int i;
+
+ for (i = 0; i < data->num_gpios; i++) {
+ sysfs_remove_link(&data->dev->kobj, data->gpios[i].name);
+ gpiod_unexport(data->gpios[i].desc);
+ }
+}
+
+static int gpio_exporter_probe(struct platform_device *pdev)
+{
+ struct device *dev = &pdev->dev;
+ struct fwnode_handle *child;
+ int num_gpios;
+ int ret;
+ struct gpio_exporter_data *data;
+
+ if (!dev->of_node)
+ return -ENODEV;
+
+ data = devm_kzalloc(dev, sizeof(*data), GFP_KERNEL);
+ if (!data)
+ return -ENOMEM;
+
+ data->dev = dev;
+ dev_set_drvdata(dev, data);
+
+ num_gpios = device_get_child_node_count(dev);
+ data->gpios = devm_kzalloc(dev, num_gpios * sizeof(*data->gpios),
+ GFP_KERNEL);
+ if (!data->gpios)
+ return -ENOMEM;
+
+ device_for_each_child_node(dev, child) {
+ ret = gpio_exporter_do_one(data, child);
+ if (ret)
+ goto out_cleanup;
+ }
+
+ dev_info(dev, "exported %d gpios\n", data->num_gpios);
+
+ return 0;
+
+out_cleanup:
+ gpio_exporter_cleanup(data);
+
+ return ret;
+}
+
+static int gpio_exporter_remove(struct platform_device *pdev)
+{
+ struct gpio_exporter_data *data = platform_get_drvdata(pdev);
+
+ gpio_exporter_cleanup(data);
+
+ return 0;
+}
+
+static const struct of_device_id gpio_exporter_dt_ids[] = {
+ { .compatible = "linux,gpio-exporter", },
+ { /* sentinel */ }
+};
+MODULE_DEVICE_TABLE(of, gpio_exporter_dt_ids);
+
+static struct platform_driver gpio_exporter_driver = {
+ .driver = {
+ .name = "gpio-exporter",
+ .of_match_table = gpio_exporter_dt_ids,
+ },
+ .probe = gpio_exporter_probe,
+ .remove = gpio_exporter_remove,
+};
+
+module_platform_driver(gpio_exporter_driver);
+
+MODULE_LICENSE("GPL v2");
+MODULE_AUTHOR("Martin Fuzzey <mfuzzey@xxxxxxxxxxx>");
+MODULE_DESCRIPTION("Userspace GPIO exporter");
+MODULE_ALIAS("platform:gpio-exporter");
--
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