[RFC 1/2] pwrseq: Add subsystem to handle complex power sequences

[Ulf Hansson]

The pwrseq subsystem handles complex power sequences, typically useful
for subsystems that makes use of discoverable buses, like for example
MMC and I2C.

The pwrseq subsystem is dependant on CONFIG_OF to be able to parse a DT
childnode to find out what power sequence method to bind for a device.

>From the DT childnode, the pwrseq DT parser tries to locate a
"power-method" property, which string is matched towards the list of
supported pwrseq methods.

Each pwrseq method implements it's own power sequence and interfaces
the pwrseq core through a few callback functions.

To instantiate a pwrseq method, clients shall use the devm_pwrseq_get()
API. If needed, clients can explicity drop the references to a pwrseq
method using devm_pwrseq_put() API.

Besides instantiation, the pwrseq API provides clients opportunity to
select a certain power state. In this intial version, PWRSEQ_POWER_ON
and PWRSEQ_POWER_OFF are supported. Those are also mandatory for each
pwrseq method to support.

Signed-off-by: Ulf Hansson <ulf.hansson@xxxxxxxxxx>
---
 .../devicetree/bindings/pwrseq/pwrseq.txt          |   48 ++++++
 drivers/Makefile                                   |    2 +-
 drivers/pwrseq/Makefile                            |    2 +
 drivers/pwrseq/core.c                              |  175 ++++++++++++++++++++
 drivers/pwrseq/core.h                              |   37 +++++
 drivers/pwrseq/method.c                            |   38 +++++
 include/linux/pwrseq.h                             |   50 ++++++
 7 files changed, 351 insertions(+), 1 deletion(-)
 create mode 100644 Documentation/devicetree/bindings/pwrseq/pwrseq.txt
 create mode 100644 drivers/pwrseq/Makefile
 create mode 100644 drivers/pwrseq/core.c
 create mode 100644 drivers/pwrseq/core.h
 create mode 100644 drivers/pwrseq/method.c
 create mode 100644 include/linux/pwrseq.h

diff --git a/Documentation/devicetree/bindings/pwrseq/pwrseq.txt b/Documentation/devicetree/bindings/pwrseq/pwrseq.txt
new file mode 100644
index 0000000..80848ae
--- /dev/null
+++ b/Documentation/devicetree/bindings/pwrseq/pwrseq.txt
@@ -0,0 +1,48 @@
+Power sequence DT bindings
+
+Each power sequence method has a corresponding "power-method" property string.
+This property shall be set in a subnode for a device. That subnode should also
+describe resourses which are specific to that power method.
+
+Do note, power sequences as such isn't encoded through DT. Instead those are
+implemented by each power method.
+
+Required subnode properties:
+- power-method: should contain the string for the power method to bind.
+
+	Supported power methods: None.
+
+Example:
+
+Note, the "clock" power method in this example isn't actually supported, but
+used to visualize how a childnode could be described.
+
+// WLAN SDIO channel
+sdi1_per2@80118000 {
+	compatible = "arm,pl18x", "arm,primecell";
+	reg = <0x80118000 0x1000>;
+	interrupts = <0 50 IRQ_TYPE_LEVEL_HIGH>;
+
+	dmas = <&dma 32 0 0x2>, /* Logical - DevToMem */
+	       <&dma 32 0 0x0>; /* Logical - MemToDev */
+	dma-names = "rx", "tx";
+
+	clocks = <&prcc_kclk 2 4>, <&prcc_pclk 2 6>;
+	clock-names = "sdi", "apb_pclk";
+
+	arm,primecell-periphid = <0x10480180>;
+	max-frequency = <100000000>;
+	bus-width = <4>;
+	non-removable;
+	pinctrl-names = "default", "sleep";
+	pinctrl-0 = <&sdi1_default_mode>;
+	pinctrl-1 = <&sdi1_sleep_mode>;
+
+	status = "okay";
+
+	pwrseq: pwrseq1 {
+		power-method = "clock";
+		clocks = <&someclk 1 2>, <&someclk 3 4>;
+		clock-names = "pwrseq1", "pwrseq2";
+	};
+};
diff --git a/drivers/Makefile b/drivers/Makefile
index f98b50d..ac1bf5b 100644
--- a/drivers/Makefile
+++ b/drivers/Makefile
@@ -128,7 +128,7 @@ endif
 obj-$(CONFIG_DCA)		+= dca/
 obj-$(CONFIG_HID)		+= hid/
 obj-$(CONFIG_PPC_PS3)		+= ps3/
-obj-$(CONFIG_OF)		+= of/
+obj-$(CONFIG_OF)		+= of/ pwrseq/
 obj-$(CONFIG_SSB)		+= ssb/
 obj-$(CONFIG_BCMA)		+= bcma/
 obj-$(CONFIG_VHOST_RING)	+= vhost/
diff --git a/drivers/pwrseq/Makefile b/drivers/pwrseq/Makefile
new file mode 100644
index 0000000..afb914f
--- /dev/null
+++ b/drivers/pwrseq/Makefile
@@ -0,0 +1,2 @@
+#Support for the power sequence subsystem
+obj-y = core.o method.o
diff --git a/drivers/pwrseq/core.c b/drivers/pwrseq/core.c
new file mode 100644
index 0000000..baf7bb6
--- /dev/null
+++ b/drivers/pwrseq/core.c
@@ -0,0 +1,175 @@
+/*
+ * Core of the power sequence subsystem
+ *
+ * Copyright (C) 2014 Linaro Ltd
+ *
+ * Author: Ulf Hansson <ulf.hansson@xxxxxxxxxx>
+ *
+ * License terms: GNU General Public License (GPL) version 2
+ */
+
+#include <linux/kernel.h>
+#include <linux/export.h>
+#include <linux/device.h>
+#include <linux/string.h>
+#include <linux/err.h>
+#include <linux/of.h>
+
+#include <linux/pwrseq.h>
+#include "core.h"
+
+static int pwrseq_find(const char *power_method)
+{
+	int i;
+
+	for (i = 0; pwrseq_methods[i].bind_method != NULL; i++)
+		if (!strcasecmp(power_method, pwrseq_methods[i].method))
+			return i;
+	return -ENODEV;
+}
+
+static void devm_pwrseq_release(struct device *dev, void *res)
+{
+	struct pwrseq *ps = res;
+
+	dev_dbg(dev, "%s: Release method=%s\n", __func__, ps->method);
+
+	ps->ps_ops->release(ps);
+	of_node_put(ps->np_child);
+}
+
+static struct pwrseq *pwrseq_get(struct device *dev,
+				struct device_node *np,
+				const char *power_method)
+{
+	struct pwrseq *ps;
+	int ret;
+
+	ret = pwrseq_find(power_method);
+	if (ret < 0)
+		return ERR_PTR(ret);
+
+	ps = devres_alloc(devm_pwrseq_release, sizeof(ps), GFP_KERNEL);
+	if (!ps)
+		return ERR_PTR(-ENOMEM);
+
+	ps->dev = dev;
+	ps->np_child = np;
+	ps->method = pwrseq_methods[ret].method;
+
+	/*
+	 * The on/off states is mandatory to be supported. Additional states
+	 * shall be added by each method during binding.
+	 */
+	ps->supported_states = PWRSEQ_POWER_OFF | PWRSEQ_POWER_ON;
+	/*
+	 * The default current state is PWRSEQ_POWER_OFF, it may be updated
+	 * during binding.
+	 */
+	ps->current_state = PWRSEQ_POWER_OFF;
+
+	ret = pwrseq_methods[ret].bind_method(ps);
+	if (ret) {
+		devres_free(ps);
+		return ERR_PTR(ret);
+	}
+
+	devres_add(dev, ps);
+	return ps;
+}
+
+static int pwrseq_of_find(struct device *dev,
+			struct device_node **np_child,
+			const char **power_method)
+{
+	struct device_node *np;
+	const char *pm;
+
+	if (!dev->of_node)
+		return -ENODEV;
+
+	/* Parse childnodes to find a power-method property. */
+	for_each_child_of_node(dev->of_node, np) {
+		if (!of_property_read_string(np, "power-method", &pm)) {
+			*np_child = np;
+			*power_method = pm;
+			return 1;
+		}
+	}
+
+	return 0;
+}
+
+static struct pwrseq *_devm_pwrseq_get(struct device *dev, bool optional)
+{
+	struct pwrseq *ps;
+	struct device_node *np;
+	const char *pm;
+	int ret;
+
+	if (!dev)
+		return ERR_PTR(-ENODEV);
+
+	ret = pwrseq_of_find(dev, &np, &pm);
+	if (ret < 0) {
+		return ERR_PTR(ret);
+	} else if (ret) {
+		ps = pwrseq_get(dev, np, pm);
+		if (IS_ERR(ps))
+			of_node_put(np);
+	} else if (optional) {
+		ps = pwrseq_get(dev, NULL, "dummy");
+	} else {
+		return ERR_PTR(-ENODEV);
+	}
+
+	if (!IS_ERR(ps))
+		dev_dbg(dev, "%s: Bound method=%s\n", __func__, ps->method);
+
+	return ps;
+}
+
+struct pwrseq *devm_pwrseq_get_optional(struct device *dev)
+{
+	return _devm_pwrseq_get(dev, true);
+}
+EXPORT_SYMBOL_GPL(devm_pwrseq_get_optional);
+
+struct pwrseq *devm_pwrseq_get(struct device *dev)
+{
+	return _devm_pwrseq_get(dev, false);
+}
+EXPORT_SYMBOL_GPL(devm_pwrseq_get);
+
+static int devm_pwrseq_match(struct device *dev, void *res, void *data)
+{
+	struct pwrseq **ps = res;
+
+	return *ps == data;
+}
+
+void devm_pwrseq_put(struct pwrseq *ps)
+{
+	devres_release(ps->dev, devm_pwrseq_release, devm_pwrseq_match, ps);
+}
+EXPORT_SYMBOL_GPL(devm_pwrseq_put);
+
+int pwrseq_select_state(struct pwrseq *ps, enum pwrseq_state ps_state)
+{
+	int ret = 0;
+
+	if (ps->current_state != ps_state)
+		ret = ps->ps_ops->select_state(ps, ps_state);
+
+	if (!ret)
+		ps->current_state = ps_state;
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(pwrseq_select_state);
+
+unsigned int pwrseq_supported_states(struct pwrseq *ps)
+{
+	return ps->supported_states;
+}
+EXPORT_SYMBOL_GPL(pwrseq_supported_states);
diff --git a/drivers/pwrseq/core.h b/drivers/pwrseq/core.h
new file mode 100644
index 0000000..84a6449
--- /dev/null
+++ b/drivers/pwrseq/core.h
@@ -0,0 +1,37 @@
+/*
+ * Core private header for the power sequence subsystem
+ *
+ * Copyright (C) 2014 Linaro Ltd
+ *
+ * Author: Ulf Hansson <ulf.hansson@xxxxxxxxxx>
+ *
+ * License terms: GNU General Public License (GPL) version 2
+ */
+
+#ifndef __PWRSEQ_PWRSEQ_H
+#define __PWRSEQ_PWRSEQ_H
+
+#include <linux/pwrseq.h>
+
+struct pwrseq_ops {
+	int (*select_state)(struct pwrseq *, enum pwrseq_state);
+	void (*release)(struct pwrseq *);
+};
+
+struct pwrseq {
+	struct device *dev;
+	struct device_node *np_child;
+	const char *method;
+	enum pwrseq_state supported_states;
+	enum pwrseq_state current_state;
+	struct pwrseq_ops *ps_ops;
+	void *data;
+};
+
+struct pwrseq_method {
+	int (*bind_method)(struct pwrseq *);
+	const char *method;
+};
+
+extern struct pwrseq_method pwrseq_methods[];
+#endif
diff --git a/drivers/pwrseq/method.c b/drivers/pwrseq/method.c
new file mode 100644
index 0000000..fe16579
--- /dev/null
+++ b/drivers/pwrseq/method.c
@@ -0,0 +1,38 @@
+/*
+ * Implements a dummy power method for power sequence subsystem
+ *
+ * Copyright (C) 2014 Linaro Ltd
+ *
+ * Author: Ulf Hansson <ulf.hansson@xxxxxxxxxx>
+ *
+ * License terms: GNU General Public License (GPL) version 2
+ */
+
+#include <linux/kernel.h>
+
+#include <linux/pwrseq.h>
+#include "core.h"
+
+static int pwrseq_dummy_select_state(struct pwrseq *ps, enum pwrseq_state s)
+{
+	return 0;
+}
+
+static void pwrseq_dummy_release(struct pwrseq *ps) { }
+
+static struct pwrseq_ops pwrseq_dummy_ops = {
+	.select_state = pwrseq_dummy_select_state,
+	.release = pwrseq_dummy_release,
+};
+
+static int pwrseq_dummy_bind(struct pwrseq *ps)
+{
+	ps->ps_ops = &pwrseq_dummy_ops;
+	return 0;
+}
+
+/* The extern list of supported power sequence_methods */
+struct pwrseq_method pwrseq_methods[] = {
+	{ pwrseq_dummy_bind, "dummy" },
+	{ NULL, NULL },
+};
diff --git a/include/linux/pwrseq.h b/include/linux/pwrseq.h
new file mode 100644
index 0000000..528b544
--- /dev/null
+++ b/include/linux/pwrseq.h
@@ -0,0 +1,50 @@
+/*
+ * Interface for the power sequence subsystem
+ *
+ * Copyright (C) 2014 Linaro Ltd
+ *
+ * Author: Ulf Hansson <ulf.hansson@xxxxxxxxxx>
+ *
+ * License terms: GNU General Public License (GPL) version 2
+ */
+#ifndef __LINUX_PWRSEQ_PWRSEQ_H
+#define __LINUX_PWRSEQ_PWRSEQ_H
+
+#include <linux/bitops.h>
+
+struct device;
+struct pwrseq;
+
+enum pwrseq_state {
+	PWRSEQ_POWER_OFF = BIT(0),
+	PWRSEQ_POWER_ON = BIT(1),
+};
+
+#ifdef CONFIG_OF
+extern struct pwrseq *devm_pwrseq_get(struct device *dev);
+extern struct pwrseq *devm_pwrseq_get_optional(struct device *dev);
+extern void devm_pwrseq_put(struct pwrseq *ps);
+extern int pwrseq_select_state(struct pwrseq *ps, unsigned int ps_state);
+extern unsigned int pwrseq_supported_states(struct pwrseq *ps);
+#else
+static inline struct pwrseq *devm_pwrseq_get(struct device *dev)
+{
+	return ERR_PTR(-ENODEV);
+}
+static inline struct pwrseq *devm_pwrseq_get_optional(struct device *dev)
+{
+	return ERR_PTR(-ENODEV);
+}
+static inline void devm_pwrseq_put(struct pwrseq *ps) {}
+static inline int pwrseq_select_state(struct pwrseq *ps,
+				enum pwrseq_state ps_state)
+{
+	return 0;
+}
+static inline unsigned int pwrseq_supported_states(struct pwrseq *ps)
+{
+	return 0;
+}
+#endif
+
+#endif /* __LINUX_PWRSEQ_PWRSEQ_H */
-- 
1.7.9.5

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