[PATCH v8] reset: Add driver for gpio-controlled reset pins

[Philipp Zabel <p.zabel-bIcnvbaLZ9MEGnE8C9+IrQ@public.gmane.org>]

This driver implements a reset controller device that toggle a gpio
connected to a reset pin of a peripheral IC. The delay between assertion
and de-assertion of the reset signal can be configured via device tree.

Signed-off-by: Philipp Zabel <p.zabel-bIcnvbaLZ9MEGnE8C9+IrQ@public.gmane.org>
Reviewed-by: Stephen Warren <swarren-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>
---
Changes since v7:
 - renamed __gpio_reset_set to gpio_reset_set
 - made delay_us signed, negative if reset-delay-us is not set
 - added error messages for reset-gpios and reset-delay-us misconfiguration
 - set drvdata before calling reset_controller_register
---
 .../devicetree/bindings/reset/gpio-reset.txt       |  35 +++++
 drivers/reset/Kconfig                              |  11 ++
 drivers/reset/Makefile                             |   1 +
 drivers/reset/gpio-reset.c                         | 174 +++++++++++++++++++++
 4 files changed, 221 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/reset/gpio-reset.txt
 create mode 100644 drivers/reset/gpio-reset.c

diff --git a/Documentation/devicetree/bindings/reset/gpio-reset.txt b/Documentation/devicetree/bindings/reset/gpio-reset.txt
new file mode 100644
index 0000000..bca5348
--- /dev/null
+++ b/Documentation/devicetree/bindings/reset/gpio-reset.txt
@@ -0,0 +1,35 @@
+GPIO reset controller
+=====================
+
+A GPIO reset controller controls a single GPIO that is connected to the reset
+pin of a peripheral IC. Please also refer to reset.txt in this directory for
+common reset controller binding usage.
+
+Required properties:
+- compatible: Should be "gpio-reset"
+- reset-gpios: A gpio used as reset line. The gpio specifier for this property
+               depends on the gpio controller that provides the gpio.
+- #reset-cells: 0, see below
+
+Optional properties:
+- reset-delay-us: delay in microseconds. The gpio reset line will be asserted for
+                  this duration to reset.
+- initially-in-reset: boolean. If not set, the initial state should be a
+                      deasserted reset line. If this property exists, the
+                      reset line should be kept in reset.
+
+example:
+
+sii902x_reset: gpio-reset {
+	compatible = "gpio-reset";
+	reset-gpios = <&gpio5 0 GPIO_ACTIVE_LOW>;
+	reset-delay-us = <10000>;
+	initially-in-reset;
+	#reset-cells = <0>;
+};
+
+/* Device with nRESET pin connected to GPIO5_0 */
+sii902x@39 {
+	/* ... */
+	resets = <&sii902x_reset>; /* active-low GPIO5_0, 10 ms delay */
+};
diff --git a/drivers/reset/Kconfig b/drivers/reset/Kconfig
index c9d04f7..1a862df 100644
--- a/drivers/reset/Kconfig
+++ b/drivers/reset/Kconfig
@@ -11,3 +11,14 @@ menuconfig RESET_CONTROLLER
 	  via GPIOs or SoC-internal reset controller modules.
 
 	  If unsure, say no.
+
+if RESET_CONTROLLER
+
+config RESET_GPIO
+	tristate "GPIO reset controller support"
+	depends on GPIOLIB && OF
+	help
+	  This driver provides support for reset lines that are controlled
+	  directly by GPIOs.
+
+endif
diff --git a/drivers/reset/Makefile b/drivers/reset/Makefile
index 1e2d83f..b854f20 100644
--- a/drivers/reset/Makefile
+++ b/drivers/reset/Makefile
@@ -1 +1,2 @@
 obj-$(CONFIG_RESET_CONTROLLER) += core.o
+obj-$(CONFIG_RESET_GPIO) += gpio-reset.o
diff --git a/drivers/reset/gpio-reset.c b/drivers/reset/gpio-reset.c
new file mode 100644
index 0000000..5d2515a
--- /dev/null
+++ b/drivers/reset/gpio-reset.c
@@ -0,0 +1,174 @@
+/*
+ * GPIO Reset Controller driver
+ *
+ * Copyright 2013 Philipp Zabel, Pengutronix
+ *
+ * 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/delay.h>
+#include <linux/err.h>
+#include <linux/gpio.h>
+#include <linux/module.h>
+#include <linux/of_gpio.h>
+#include <linux/platform_device.h>
+#include <linux/reset-controller.h>
+
+struct gpio_reset_data {
+	struct reset_controller_dev rcdev;
+	unsigned int gpio;
+	bool active_low;
+	s32 delay_us;
+};
+
+static void gpio_reset_set(struct reset_controller_dev *rcdev, int asserted)
+{
+	struct gpio_reset_data *drvdata = container_of(rcdev,
+			struct gpio_reset_data, rcdev);
+	int value = asserted;
+
+	if (drvdata->active_low)
+		value = !value;
+
+	gpio_set_value(drvdata->gpio, value);
+}
+
+static int gpio_reset(struct reset_controller_dev *rcdev, unsigned long id)
+{
+	struct gpio_reset_data *drvdata = container_of(rcdev,
+			struct gpio_reset_data, rcdev);
+
+	if (drvdata->delay_us < 0)
+		return -ENOSYS;
+
+	gpio_reset_set(rcdev, 1);
+	udelay(drvdata->delay_us);
+	gpio_reset_set(rcdev, 0);
+
+	return 0;
+}
+
+static int gpio_reset_assert(struct reset_controller_dev *rcdev,
+		unsigned long id)
+{
+	gpio_reset_set(rcdev, 1);
+
+	return 0;
+}
+
+static int gpio_reset_deassert(struct reset_controller_dev *rcdev,
+		unsigned long id)
+{
+	gpio_reset_set(rcdev, 0);
+
+	return 0;
+}
+
+static struct reset_control_ops gpio_reset_ops = {
+	.reset = gpio_reset,
+	.assert = gpio_reset_assert,
+	.deassert = gpio_reset_deassert,
+};
+
+static int of_gpio_reset_xlate(struct reset_controller_dev *rcdev,
+			       const struct of_phandle_args *reset_spec)
+{
+	if (WARN_ON(reset_spec->args_count != 0))
+		return -EINVAL;
+
+	return 0;
+}
+
+static int gpio_reset_probe(struct platform_device *pdev)
+{
+	struct device_node *np = pdev->dev.of_node;
+	struct gpio_reset_data *drvdata;
+	enum of_gpio_flags flags;
+	unsigned long gpio_flags;
+	bool initially_in_reset;
+	int ret;
+
+	drvdata = devm_kzalloc(&pdev->dev, sizeof(*drvdata), GFP_KERNEL);
+	if (drvdata == NULL)
+		return -ENOMEM;
+
+	if (of_gpio_named_count(np, "reset-gpios") != 1) {
+		dev_err(&pdev->dev,
+			"reset-gpios property missing, or not a single gpio\n");
+		return -EINVAL;
+	}
+
+	drvdata->gpio = of_get_named_gpio_flags(np, "reset-gpios", 0, &flags);
+	if (drvdata->gpio == -EPROBE_DEFER) {
+		return drvdata->gpio;
+	} else if (!gpio_is_valid(drvdata->gpio)) {
+		dev_err(&pdev->dev, "invalid reset gpio: %d\n", drvdata->gpio);
+		return drvdata->gpio;
+	}
+
+	drvdata->active_low = flags & OF_GPIO_ACTIVE_LOW;
+
+	ret = of_property_read_u32(np, "reset-delay-us", &drvdata->delay_us);
+	if (ret < 0)
+		drvdata->delay_us = -1;
+	else if (drvdata->delay_us < 0)
+		dev_warn(&pdev->dev, "reset delay too high\n");
+
+	initially_in_reset = of_property_read_bool(np, "initially-in-reset");
+	if (drvdata->active_low ^ initially_in_reset)
+		gpio_flags = GPIOF_OUT_INIT_HIGH;
+	else
+		gpio_flags = GPIOF_OUT_INIT_LOW;
+
+	ret = devm_gpio_request_one(&pdev->dev, drvdata->gpio, gpio_flags, NULL);
+	if (ret < 0) {
+		dev_err(&pdev->dev, "failed to request gpio %d: %d\n",
+			drvdata->gpio, ret);
+		return ret;
+	}
+
+	platform_set_drvdata(pdev, drvdata);
+
+	drvdata->rcdev.of_node = np;
+	drvdata->rcdev.owner = THIS_MODULE;
+	drvdata->rcdev.nr_resets = 1;
+	drvdata->rcdev.ops = &gpio_reset_ops;
+	drvdata->rcdev.of_xlate = of_gpio_reset_xlate;
+	reset_controller_register(&drvdata->rcdev);
+
+	return 0;
+}
+
+static int gpio_reset_remove(struct platform_device *pdev)
+{
+	struct gpio_reset_data *drvdata = platform_get_drvdata(pdev);
+
+	reset_controller_unregister(&drvdata->rcdev);
+
+	return 0;
+}
+
+static struct of_device_id gpio_reset_dt_ids[] = {
+	{ .compatible = "gpio-reset" },
+	{ }
+};
+
+static struct platform_driver gpio_reset_driver = {
+	.probe = gpio_reset_probe,
+	.remove = gpio_reset_remove,
+	.driver = {
+		.name = "gpio-reset",
+		.owner = THIS_MODULE,
+		.of_match_table = of_match_ptr(gpio_reset_dt_ids),
+	},
+};
+
+module_platform_driver(gpio_reset_driver);
+
+MODULE_AUTHOR("Philipp Zabel <p.zabel-bIcnvbaLZ9MEGnE8C9+IrQ@public.gmane.org>");
+MODULE_DESCRIPTION("gpio reset controller");
+MODULE_LICENSE("GPL");
+MODULE_ALIAS("platform:gpio-reset");
+MODULE_DEVICE_TABLE(of, gpio_reset_dt_ids);
-- 
1.8.2.rc2