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

["Andrew F. Davis" <afd@ti.com>]

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@ti.com>
[s-anna@ti.com: add documentation, syscon name change]
Signed-off-by: Suman Anna <s-anna@ti.com>
---
 drivers/reset/Kconfig        |  10 ++
 drivers/reset/Makefile       |   1 +
 drivers/reset/reset-syscon.c | 259 +++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 270 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..48c8c30
--- /dev/null
+++ b/drivers/reset/reset-syscon.c
@@ -0,0 +1,259 @@
+/*
+ * SYSCON regmap reset driver
+ *
+ * Copyright (C) 2015 Texas Instruments Incorporated - http://www.ti.com/
+ *	Andrew F. Davis <afd@ti.com>
+ *	Suman Anna <afd@ti.com>
+ *
+ * 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/idr.h>
+#include <linux/mfd/syscon.h>
+#include <linux/module.h>
+#include <linux/of.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
+ */
+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;
+};
+
+/**
+ * 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;
+	struct idr idr;
+};
+
+#define to_syscon_reset_data(rcdev)	\
+	container_of(rcdev, struct syscon_reset_data, rcdev)
+
+/**
+ * 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;
+
+	control = idr_find(&data->idr, id);
+	if (!control)
+		return -EINVAL;
+
+	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, or a non-zero value if reset is asserted
+ */
+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;
+
+	control = idr_find(&data->idr, id);
+	if (!control)
+		return -EINVAL;
+
+	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,
+};
+
+/**
+ * syscon_reset_of_xlate() - translate a set of OF arguments to a reset ID
+ * @rcdev: reset controller entity
+ * @reset_spec: OF reset argument specifier
+ *
+ * This function performs the translation of the reset argument specifier
+ * values defined in a reset consumer device node. The function allocates a
+ * reset control structure for that device reset, that will be used by the
+ * driver for performing any reset functions on that reset. An idr structure
+ * is allocated and used to map to the reset control structure. This idr is
+ * used by the driver to do reset lookups.
+ *
+ * Return: 0 for successful request, else a corresponding error value
+ */
+static int syscon_reset_of_xlate(struct reset_controller_dev *rcdev,
+				 const struct of_phandle_args *reset_spec)
+{
+	struct syscon_reset_data *data = to_syscon_reset_data(rcdev);
+	struct syscon_reset_control *control;
+
+	if (WARN_ON(reset_spec->args_count != 6))
+		return -EINVAL;
+
+	control = devm_kzalloc(data->dev, sizeof(*control), GFP_KERNEL);
+	if (!control)
+		return -ENOMEM;
+
+	control->offset = reset_spec->args[0];
+	control->reset_bit = reset_spec->args[1];
+	control->assert_high = reset_spec->args[2] == 1;
+	control->status_offset = reset_spec->args[3];
+	control->status_reset_bit = reset_spec->args[4];
+	control->status_assert_high = reset_spec->args[5] == 1;
+
+	return idr_alloc(&data->idr, control, 0, 0, GFP_KERNEL);
+}
+
+static int syscon_reset_probe(struct platform_device *pdev)
+{
+	struct syscon_reset_data *data;
+	struct device_node *np = pdev->dev.of_node;
+	struct regmap *memory;
+
+	if (!np)
+		return -ENODEV;
+
+	data = devm_kzalloc(&pdev->dev, sizeof(*data), GFP_KERNEL);
+	if (!data)
+		return -ENOMEM;
+
+	memory = syscon_regmap_lookup_by_phandle(np, "syscon");
+	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.of_xlate = syscon_reset_of_xlate;
+	data->dev = &pdev->dev;
+	data->memory = memory;
+	idr_init(&data->idr);
+
+	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);
+
+	idr_destroy(&data->idr);
+
+	return 0;
+}
+
+static const struct of_device_id syscon_reset_of_match_table[] = {
+	{ .compatible = "syscon-reset", },
+	{ /* sentinel */ },
+};
+MODULE_DEVICE_TABLE(of, syscon_reset_of_match_table);
+
+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_table,
+	},
+};
+module_platform_driver(syscon_reset_driver);
+
+MODULE_AUTHOR("Andrew F. Davis <afd@ti.com>");
+MODULE_AUTHOR("Suman Anna <s-anna@ti.com>");
+MODULE_DESCRIPTION("SYSCON Regmap Reset Driver");
+MODULE_LICENSE("GPL v2");
-- 
2.7.0