[PATCH v2 2/2] reset: add a SYSCON based reset driver

[Andrew F. Davis]

Add a reset-controller driver for performing reset management of
various devices present on the SoC, with the reset registers shared
between devices in a common register memory space. This driver uses
the syscon/regmap frameworks to actually implement the various reset
functionalities needed by the reset consumer devices.

Signed-off-by: Andrew F. Davis <afd@xxxxxx>
[s-anna@xxxxxx: add documentation, syscon name change]
Signed-off-by: Suman Anna <s-anna@xxxxxx>
---
 drivers/reset/Kconfig        |  10 ++
 drivers/reset/Makefile       |   1 +
 drivers/reset/reset-syscon.c | 283 +++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 294 insertions(+)
 create mode 100644 drivers/reset/reset-syscon.c

diff --git a/drivers/reset/Kconfig b/drivers/reset/Kconfig
index df37212..5f26755 100644
--- a/drivers/reset/Kconfig
+++ b/drivers/reset/Kconfig
@@ -12,5 +12,15 @@ menuconfig RESET_CONTROLLER
 
 	  If unsure, say no.
 
+config SYSCON_RESET
+	tristate "SYSCON Reset Driver"
+	depends on RESET_CONTROLLER
+	select MFD_SYSCON
+	help
+	  This enables the reset driver support for devices with memory-mapped
+	  reset registers as part of a syscon device node. If you wish to use
+	  the reset framework for such memory-mapped devices, say Y here.
+	  Otherwise, say N.
+
 source "drivers/reset/sti/Kconfig"
 source "drivers/reset/hisilicon/Kconfig"
diff --git a/drivers/reset/Makefile b/drivers/reset/Makefile
index 4d7178e..6b3f6e3 100644
--- a/drivers/reset/Makefile
+++ b/drivers/reset/Makefile
@@ -7,3 +7,4 @@ obj-$(CONFIG_ARCH_STI) += sti/
 obj-$(CONFIG_ARCH_HISI) += hisilicon/
 obj-$(CONFIG_ARCH_ZYNQ) += reset-zynq.o
 obj-$(CONFIG_ATH79) += reset-ath79.o
+obj-$(CONFIG_SYSCON_RESET) += reset-syscon.o
diff --git a/drivers/reset/reset-syscon.c b/drivers/reset/reset-syscon.c
new file mode 100644
index 0000000..d127c83
--- /dev/null
+++ b/drivers/reset/reset-syscon.c
@@ -0,0 +1,283 @@
+/*
+ * SYSCON regmap reset driver
+ *
+ * Copyright (C) 2015-2016 Texas Instruments Incorporated - http://www.ti.com/
+ *	Andrew F. Davis <afd@xxxxxx>
+ *	Suman Anna <afd@xxxxxx>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed "as is" WITHOUT ANY WARRANTY of any
+ * kind, whether express or implied; without even the implied warranty
+ * of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ */
+
+#include <linux/mfd/syscon.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/of_address.h>
+#include <linux/platform_device.h>
+#include <linux/regmap.h>
+#include <linux/reset-controller.h>
+
+/**
+ * struct syscon_reset_control - reset control structure
+ * @offset: reset control register offset from syscon base
+ * @reset_bit: reset bit in the reset control register
+ * @assert_high: flag to indicate if setting the bit high asserts the reset
+ * @status_offset: reset status register offset from syscon base
+ * @status_reset_bit: reset status bit in the reset status register
+ * @status_assert_high: flag to indicate if a set bit represents asserted state
+ * @toggle: flag to indicate this reset has no readable status register
+ */
+struct syscon_reset_control {
+	unsigned int offset;
+	unsigned int reset_bit;
+	bool assert_high;
+	unsigned int status_offset;
+	unsigned int status_reset_bit;
+	bool status_assert_high;
+	bool toggle;
+};
+
+/**
+ * struct syscon_reset_data - reset controller information structure
+ * @rcdev: reset controller entity
+ * @dev: reset controller device pointer
+ * @memory: regmap handle containing the memory-mapped reset registers
+ * @idr: idr structure for mapping ids to reset control structures
+ */
+struct syscon_reset_data {
+	struct reset_controller_dev rcdev;
+	struct device *dev;
+	struct regmap *memory;
+};
+
+#define to_syscon_reset_data(rcdev)	\
+	container_of(rcdev, struct syscon_reset_data, rcdev)
+
+/**
+ * syscon_reset_get_control() - get reset control info from DT node
+ * @data: reset controller data
+ * @id: ID address of control data node
+ * @control: control data struct to fill
+ *
+ * Search DT for a child node at the specified address that contains
+ * reset control info and use that to fill in control data.
+ *
+ * Return: 0 for successful request, else a corresponding error value
+ */
+static int syscon_reset_get_control(struct syscon_reset_data *data,
+				    unsigned long id,
+				    struct syscon_reset_control *control)
+{
+	struct device_node *child;
+	const __be32 *address;
+	const __be32 *list;
+	int size;
+
+	for_each_child_of_node(data->rcdev.of_node, child) {
+		address = of_get_address(child, 0, NULL, NULL);
+		if (!address || be32_to_cpup(address) != id)
+			continue;
+
+		list = of_get_property(child, "reset-control", &size);
+		if (!list || size != (3 * sizeof(*list)))
+			return -EINVAL;
+		control->offset = be32_to_cpup(list++);
+		control->reset_bit = be32_to_cpup(list++);
+		control->assert_high = be32_to_cpup(list) == 1;
+
+		if (of_find_property(child, "reset-toggle", NULL)) {
+			control->toggle = true;
+			return 0;
+		}
+		control->toggle = false;
+
+		list = of_get_property(child, "reset-status", &size);
+		if (!list) {
+			/* use control register values */
+			control->status_offset = control->offset;
+			control->status_reset_bit = control->reset_bit;
+			control->status_assert_high = control->assert_high;
+			return 0;
+		}
+
+		if (size != (3 * sizeof(*list)))
+			return -EINVAL;
+		control->status_offset = be32_to_cpup(list++);
+		control->status_reset_bit = be32_to_cpup(list++);
+		control->status_assert_high = be32_to_cpup(list) == 1;
+		return 0;
+	}
+
+	return -ENOENT;
+}
+
+/**
+ * syscon_reset_set() - program a device's reset
+ * @rcdev: reset controller entity
+ * @id: ID of the reset to toggle
+ * @assert: boolean flag to indicate assert or deassert
+ *
+ * This is a common internal function used to assert or deassert a device's
+ * reset using the regmap API. The device's reset is asserted if the @assert
+ * argument is true, or deasserted if the @assert argument is false.
+ *
+ * Return: 0 for successful request, else a corresponding error value
+ */
+static int syscon_reset_set(struct reset_controller_dev *rcdev,
+			    unsigned long id, bool assert)
+{
+	struct syscon_reset_data *data = to_syscon_reset_data(rcdev);
+	struct syscon_reset_control control;
+	unsigned int mask, value;
+	int ret;
+
+	ret = syscon_reset_get_control(data, id, &control);
+	if (ret)
+		return ret;
+
+	mask = BIT(control.reset_bit);
+	value = (assert == control.assert_high) ? mask : 0x0;
+
+	return regmap_update_bits(data->memory, control.offset, mask, value);
+}
+
+/**
+ * syscon_reset_assert() - assert device reset
+ * @rcdev: reset controller entity
+ * @id: ID of the reset to be asserted
+ *
+ * This function implements the reset driver op to assert a device's reset.
+ * This invokes the function syscon_reset_set() with the corresponding
+ * parameters as passed in, but with the @assert argument set to true for
+ * asserting the reset.
+ *
+ * Return: 0 for successful request, else a corresponding error value
+ */
+static int syscon_reset_assert(struct reset_controller_dev *rcdev,
+			       unsigned long id)
+{
+	return syscon_reset_set(rcdev, id, true);
+}
+
+/**
+ * syscon_reset_deassert() - deassert device reset
+ * @rcdev: reset controller entity
+ * @id: ID of reset to be deasserted
+ *
+ * This function implements the reset driver op to deassert a device's reset.
+ * This invokes the function syscon_reset_set() with the corresponding
+ * parameters as passed in, but with the @assert argument set to false for
+ * deasserting the reset.
+ *
+ * Return: 0 for successful request, else a corresponding error value
+ */
+static int syscon_reset_deassert(struct reset_controller_dev *rcdev,
+				 unsigned long id)
+{
+	return syscon_reset_set(rcdev, id, false);
+}
+
+/**
+ * syscon_reset_status() - check device reset status
+ * @rcdev: reset controller entity
+ * @id: ID of the reset for which the status is being requested
+ *
+ * This function implements the reset driver op to return the status of a
+ * device's reset.
+ *
+ * Return: 0 if reset is deasserted, true if reset is asserted, else a
+ * corresponding error value
+ */
+static int syscon_reset_status(struct reset_controller_dev *rcdev,
+			       unsigned long id)
+{
+	struct syscon_reset_data *data = to_syscon_reset_data(rcdev);
+	struct syscon_reset_control control;
+	unsigned int reset_state;
+	int ret;
+
+	ret = syscon_reset_get_control(data, id, &control);
+	if (ret)
+		return ret;
+
+	if (control.toggle)
+		return -ENOSYS; /* status not supported for this reset */
+
+	ret = regmap_read(data->memory, control.status_offset, &reset_state);
+	if (ret)
+		return ret;
+
+	return (reset_state & BIT(control.status_reset_bit)) ==
+			control.status_assert_high;
+}
+
+static struct reset_control_ops syscon_reset_ops = {
+	.assert		= syscon_reset_assert,
+	.deassert	= syscon_reset_deassert,
+	.status		= syscon_reset_status,
+};
+
+static int syscon_reset_probe(struct platform_device *pdev)
+{
+	struct syscon_reset_data *data;
+	struct device *dev = &pdev->dev;
+	struct device_node *np = dev->of_node;
+	struct regmap *memory;
+
+	if (!np)
+		return -ENODEV;
+
+	data = devm_kzalloc(dev, sizeof(*data), GFP_KERNEL);
+	if (!data)
+		return -ENOMEM;
+
+	memory = syscon_node_to_regmap(np->parent);
+	if (IS_ERR(memory))
+		return PTR_ERR(memory);
+
+	data->rcdev.ops = &syscon_reset_ops;
+	data->rcdev.owner = THIS_MODULE;
+	data->rcdev.of_node = np;
+	data->rcdev.nr_resets = of_get_child_count(np);
+	data->dev = dev;
+	data->memory = memory;
+	platform_set_drvdata(pdev, data);
+
+	return reset_controller_register(&data->rcdev);
+}
+
+static int syscon_reset_remove(struct platform_device *pdev)
+{
+	struct syscon_reset_data *data = platform_get_drvdata(pdev);
+
+	reset_controller_unregister(&data->rcdev);
+
+	return 0;
+}
+
+static const struct of_device_id syscon_reset_of_match[] = {
+	{ .compatible = "syscon-reset", },
+	{ /* sentinel */ },
+};
+MODULE_DEVICE_TABLE(of, syscon_reset_of_match);
+
+static struct platform_driver syscon_reset_driver = {
+	.probe = syscon_reset_probe,
+	.remove = syscon_reset_remove,
+	.driver = {
+		.name = "syscon-reset",
+		.of_match_table = syscon_reset_of_match,
+	},
+};
+module_platform_driver(syscon_reset_driver);
+
+MODULE_AUTHOR("Andrew F. Davis <afd@xxxxxx>");
+MODULE_AUTHOR("Suman Anna <s-anna@xxxxxx>");
+MODULE_DESCRIPTION("SYSCON Regmap Reset Driver");
+MODULE_LICENSE("GPL v2");
-- 
2.7.2