[PATCH 2/3] Add support for monitoring gpio switches

[Martyn Welch <martyn.welch@collabora.co.uk>]

Select Chromebooks have gpio attached to switches used to cause the
firmware to enter alternative modes of operation and/or control other
device characteristics (such as write protection on flash devices). This
patch adds a driver that exposes a read-only interface to allow these
signals to be read from user space.

This functionality has been generalised to provide support for any device
with device tree support which needs to identify a gpio as being used for a
specific task.

Signed-off-by: Martyn Welch <martyn.welch@collabora.co.uk>
---
 drivers/misc/Kconfig       |  11 ++++
 drivers/misc/Makefile      |   1 +
 drivers/misc/gpio-switch.c | 160 +++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 172 insertions(+)
 create mode 100644 drivers/misc/gpio-switch.c

diff --git a/drivers/misc/Kconfig b/drivers/misc/Kconfig
index 22892c7..d24367c 100644
--- a/drivers/misc/Kconfig
+++ b/drivers/misc/Kconfig
@@ -525,6 +525,17 @@ config VEXPRESS_SYSCFG
 	  bus. System Configuration interface is one of the possible means
 	  of generating transactions on this bus.
 
+config GPIO_SWITCH
+	tristate "GPIO Switch driver"
+	depends on GPIO_SYSFS
+	---help---
+	 Some devices have gpio attached to dedicated switches, an example of
+	 this are chromebooks (where connection to some switches for predefined
+	 purposes are provided on the generic development card). This driver
+	 provides the ability to create consistently named sysfs entries to the
+	 functionally equivalent signals across a range of devices. This
+	 functionality currently requires a device which supports device tree.
+
 source "drivers/misc/c2port/Kconfig"
 source "drivers/misc/eeprom/Kconfig"
 source "drivers/misc/cb710/Kconfig"
diff --git a/drivers/misc/Makefile b/drivers/misc/Makefile
index 537d7f3..7a7e11a 100644
--- a/drivers/misc/Makefile
+++ b/drivers/misc/Makefile
@@ -56,3 +56,4 @@ obj-$(CONFIG_GENWQE)		+= genwqe/
 obj-$(CONFIG_ECHO)		+= echo/
 obj-$(CONFIG_VEXPRESS_SYSCFG)	+= vexpress-syscfg.o
 obj-$(CONFIG_CXL_BASE)		+= cxl/
+obj-$(CONFIG_GPIO_SWITCH)	+= gpio-switch.o
diff --git a/drivers/misc/gpio-switch.c b/drivers/misc/gpio-switch.c
new file mode 100644
index 0000000..1f381d6
--- /dev/null
+++ b/drivers/misc/gpio-switch.c
@@ -0,0 +1,160 @@
+/*
+ * Copyright (C) 2015 Collabora Ltd.
+ *
+ * based on vendor driver,
+ *
+ * Copyright (C) 2011 The Chromium OS Authors
+ *
+ * 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.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ */
+#include <linux/bcd.h>
+#include <linux/gpio.h>
+#include <linux/notifier.h>
+#include <linux/io.h>
+#include <linux/of.h>
+#include <linux/of_gpio.h>
+#include <linux/platform_device.h>
+#include <linux/slab.h>
+
+struct gpio_switch_gpio_info {
+	int gpio;
+	const char *link;
+};
+
+static int dt_gpio_init(struct platform_device *pdev, struct device_node *child,
+			struct gpio_switch_gpio_info *gpio)
+{
+	int err;
+	enum of_gpio_flags of_flags;
+	unsigned long flags = GPIOF_DIR_IN | GPIOF_EXPORT;
+	const char *name;
+
+	err = of_property_read_string(child, "label", &name);
+	if (err)
+		return err;
+
+	gpio->gpio = of_get_named_gpio_flags(child, "gpios", 0, &of_flags);
+	if (!gpio_is_valid(gpio->gpio)) {
+		err = -EINVAL;
+		goto err_prop;
+	}
+
+	if (of_flags & OF_GPIO_ACTIVE_LOW)
+		flags |= GPIOF_ACTIVE_LOW;
+
+	if (!of_property_read_bool(child, "read-only"))
+		flags |= GPIOF_EXPORT_CHANGEABLE;
+
+	err = gpio_request_one(gpio->gpio, flags, name);
+	if (err)
+		goto err_prop;
+
+	err = gpio_export_link(&pdev->dev, name, gpio->gpio);
+	if (err)
+		goto err_gpio;
+
+	gpio->link = name;
+
+	return 0;
+
+err_gpio:
+	gpio_free(gpio->gpio);
+err_prop:
+	of_node_put(child);
+
+	return err;
+}
+
+static void gpio_switch_rem(struct device *dev,
+			    struct gpio_switch_gpio_info *gpio)
+{
+	sysfs_remove_link(&dev->kobj, gpio->link);
+
+	gpio_unexport(gpio->gpio);
+
+	gpio_free(gpio->gpio);
+}
+
+static int gpio_switch_probe(struct platform_device *pdev)
+{
+	struct gpio_switch_gpio_info *gpios;
+	struct device_node *child;
+	struct device_node *np = pdev->dev.of_node;
+	int ret;
+	int i;
+
+	i = of_get_child_count(np);
+	if (i < 1)
+		return i;
+
+	gpios = devm_kmalloc(&pdev->dev, sizeof(gpios) * i, GFP_KERNEL);
+	if (!gpios)
+		return -ENOMEM;
+
+	i = 0;
+
+	for_each_child_of_node(np, child) {
+		ret = dt_gpio_init(pdev, child, &gpios[i]);
+		if (ret) {
+			dev_err(&pdev->dev, "Failed to init child node %d.\n",
+				i);
+			goto err;
+		}
+
+		i++;
+	}
+
+	platform_set_drvdata(pdev, gpios);
+
+	return 0;
+
+err:
+	while (i > 0) {
+		i--;
+		gpio_switch_rem(&pdev->dev, &gpios[i]);
+	}
+
+	return ret;
+}
+
+static int gpio_switch_remove(struct platform_device *pdev)
+{
+	struct gpio_switch_gpio_info *gpios = platform_get_drvdata(pdev);
+	struct device_node *np = pdev->dev.of_node;
+	int i;
+
+	i = of_get_child_count(np);
+
+	while (i > 0) {
+		i--;
+		gpio_switch_rem(&pdev->dev, &gpios[i]);
+	}
+
+	return 0;
+}
+
+static const struct of_device_id gpio_switch_of_match[] = {
+	{ .compatible = "gpio-switch" },
+	{ }
+};
+MODULE_DEVICE_TABLE(of, gpio_switch_of_match);
+
+static struct platform_driver gpio_switch_driver = {
+	.probe = gpio_switch_probe,
+	.remove = gpio_switch_remove,
+	.driver = {
+		.name = "gpio_switch",
+		.of_match_table = gpio_switch_of_match,
+	},
+};
+module_platform_driver(gpio_switch_driver);
+
+MODULE_LICENSE("GPL");
-- 
2.1.4