[PATCH v3 1/5] reset: gpio: Add GPIO-based reset controller

[Krzysztof Kozlowski <krzysztof.kozlowski@xxxxxxxxxx>]

Add a simple driver to control GPIO-based resets using the reset
controller API for the cases when the GPIOs are shared and reset should
be coordinated.  The driver is expected to be used by reset core
framework for ad-hoc reset controllers.

Cc: Bartosz Golaszewski <brgl@xxxxxxxx>
Cc: Chris Packham <chris.packham@xxxxxxxxxxxxxxxxxxx>
Cc: Sean Anderson <sean.anderson@xxxxxxxx>
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@xxxxxxxxxx>
---
 MAINTAINERS                |   5 ++
 drivers/reset/Kconfig      |   9 +++
 drivers/reset/Makefile     |   1 +
 drivers/reset/reset-gpio.c | 121 +++++++++++++++++++++++++++++++++++++
 4 files changed, 136 insertions(+)
 create mode 100644 drivers/reset/reset-gpio.c

diff --git a/MAINTAINERS b/MAINTAINERS
index 7fe27cd60e1b..a0fbd4814bc7 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -8866,6 +8866,11 @@ F:	Documentation/i2c/muxes/i2c-mux-gpio.rst
 F:	drivers/i2c/muxes/i2c-mux-gpio.c
 F:	include/linux/platform_data/i2c-mux-gpio.h
 
+GENERIC GPIO RESET DRIVER
+M:	Krzysztof Kozlowski <krzysztof.kozlowski@xxxxxxxxxx>
+S:	Maintained
+F:	drivers/reset/reset-gpio.c
+
 GENERIC HDLC (WAN) DRIVERS
 M:	Krzysztof Halasa <khc@xxxxxxxxx>
 S:	Maintained
diff --git a/drivers/reset/Kconfig b/drivers/reset/Kconfig
index ccd59ddd7610..bb1b5a326eb7 100644
--- a/drivers/reset/Kconfig
+++ b/drivers/reset/Kconfig
@@ -66,6 +66,15 @@ config RESET_BRCMSTB_RESCAL
 	  This enables the RESCAL reset controller for SATA, PCIe0, or PCIe1 on
 	  BCM7216.
 
+config RESET_GPIO
+	tristate "GPIO reset controller"
+	help
+	  This enables a generic reset controller for resets attached via
+	  GPIOs.  Typically for OF platforms this driver expects "reset-gpios"
+	  property.
+
+	  If compiled as module, it will be called reset-gpio.
+
 config RESET_HSDK
 	bool "Synopsys HSDK Reset Driver"
 	depends on HAS_IOMEM
diff --git a/drivers/reset/Makefile b/drivers/reset/Makefile
index 8270da8a4baa..fd8b49fa46fc 100644
--- a/drivers/reset/Makefile
+++ b/drivers/reset/Makefile
@@ -11,6 +11,7 @@ obj-$(CONFIG_RESET_BCM6345) += reset-bcm6345.o
 obj-$(CONFIG_RESET_BERLIN) += reset-berlin.o
 obj-$(CONFIG_RESET_BRCMSTB) += reset-brcmstb.o
 obj-$(CONFIG_RESET_BRCMSTB_RESCAL) += reset-brcmstb-rescal.o
+obj-$(CONFIG_RESET_GPIO) += reset-gpio.o
 obj-$(CONFIG_RESET_HSDK) += reset-hsdk.o
 obj-$(CONFIG_RESET_IMX7) += reset-imx7.o
 obj-$(CONFIG_RESET_INTEL_GW) += reset-intel-gw.o
diff --git a/drivers/reset/reset-gpio.c b/drivers/reset/reset-gpio.c
new file mode 100644
index 000000000000..0fe482740f1b
--- /dev/null
+++ b/drivers/reset/reset-gpio.c
@@ -0,0 +1,121 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/gpio/consumer.h>
+#include <linux/mod_devicetable.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/platform_device.h>
+#include <linux/reset-controller.h>
+
+struct reset_gpio_priv {
+	struct reset_controller_dev rc;
+	struct gpio_desc *reset;
+};
+
+static inline struct reset_gpio_priv
+*rc_to_reset_gpio(struct reset_controller_dev *rc)
+{
+	return container_of(rc, struct reset_gpio_priv, rc);
+}
+
+static int reset_gpio_assert(struct reset_controller_dev *rc, unsigned long id)
+{
+	struct reset_gpio_priv *priv = rc_to_reset_gpio(rc);
+
+	gpiod_set_value_cansleep(priv->reset, 1);
+
+	return 0;
+}
+
+static int reset_gpio_deassert(struct reset_controller_dev *rc,
+			       unsigned long id)
+{
+	struct reset_gpio_priv *priv = rc_to_reset_gpio(rc);
+
+	gpiod_set_value_cansleep(priv->reset, 0);
+
+	return 0;
+}
+
+static int reset_gpio_status(struct reset_controller_dev *rc, unsigned long id)
+{
+	struct reset_gpio_priv *priv = rc_to_reset_gpio(rc);
+
+	return gpiod_get_value_cansleep(priv->reset);
+}
+
+static const struct reset_control_ops reset_gpio_ops = {
+	.assert = reset_gpio_assert,
+	.deassert = reset_gpio_deassert,
+	.status = reset_gpio_status,
+};
+
+static int reset_gpio_of_xlate(struct reset_controller_dev *rcdev,
+			       const struct of_phandle_args *reset_spec)
+{
+	return reset_spec->args[0];
+}
+
+static void reset_gpio_of_node_put(void *data)
+{
+	of_node_put(data);
+}
+
+static int reset_gpio_probe(struct platform_device *pdev)
+{
+	struct device *dev = &pdev->dev;
+	struct of_phandle_args *platdata = dev_get_platdata(dev);
+	struct reset_gpio_priv *priv;
+	int ret;
+
+	if (!platdata)
+		return -EINVAL;
+
+	priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
+	if (!priv)
+		return -ENOMEM;
+
+	platform_set_drvdata(pdev, &priv->rc);
+
+	/* Relies on GPIO_LOOKUP */
+	priv->reset = devm_gpiod_get(dev, "reset", GPIOD_OUT_HIGH);
+	if (IS_ERR(priv->reset))
+		return dev_err_probe(dev, PTR_ERR(priv->reset),
+				     "Could not get reset gpios\n");
+
+	priv->rc.ops = &reset_gpio_ops;
+	priv->rc.owner = THIS_MODULE;
+	priv->rc.dev = dev;
+	priv->rc.of_args = platdata;
+	priv->rc.of_node = of_node_get(platdata->np);
+	ret = devm_add_action_or_reset(dev, reset_gpio_of_node_put,
+				       priv->rc.of_node);
+	if (ret)
+		return ret;
+
+	/* Cells to match GPIO specifier, but it's not really used */
+	priv->rc.of_reset_n_cells = 2;
+	priv->rc.of_xlate = reset_gpio_of_xlate;
+	priv->rc.nr_resets = 1;
+
+	return devm_reset_controller_register(dev, &priv->rc);
+}
+
+static const struct platform_device_id reset_gpio_ids[] = {
+	{ .name = "reset-gpio", },
+	{}
+};
+MODULE_DEVICE_TABLE(platform, reset_gpio_ids);
+
+static struct platform_driver reset_gpio_driver = {
+	.probe		= reset_gpio_probe,
+	.id_table	= reset_gpio_ids,
+	.driver	= {
+		.name = "reset-gpio",
+	},
+};
+module_platform_driver(reset_gpio_driver);
+
+MODULE_AUTHOR("Krzysztof Kozlowski <krzysztof.kozlowski@xxxxxxxxxx>");
+MODULE_DESCRIPTION("Generic GPIO reset driver");
+MODULE_LICENSE("GPL");
-- 
2.34.1