[PATCH 4/4] tty/slaves: add a driver to power on/off UART attached devices.

[NeilBrown]

If a platform has a particular device permanently attached to a UART,
there may be out-of-band signaling necessary to power the device
on and off.

This driver controls that signalling for a number of different devices.
It can
 - enable/disable a regulator
 - toggle a GPIO
 - register an 'rfkill' which can force the device to be off.

When the rfkill is absent or unblocked, the device will be on when the
associated tty device is open, and closed otherwise.

Signed-off-by: NeilBrown <neil@xxxxxxxxxx>
---
 .../bindings/uart_slave/wi2wi,w2cbw003.txt         |   19 +
 .../bindings/uart_slave/wi2wi,w2sg0004.txt         |   37 +
 .../devicetree/bindings/vendor-prefixes.txt        |    1 
 drivers/tty/serial/slave/Kconfig                   |   15 +
 drivers/tty/serial/slave/Makefile                  |    1 
 drivers/tty/serial/slave/serial-power-manager.c    |  510 ++++++++++++++++++++
 6 files changed, 583 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/uart_slave/wi2wi,w2cbw003.txt
 create mode 100644 Documentation/devicetree/bindings/uart_slave/wi2wi,w2sg0004.txt
 create mode 100644 drivers/tty/serial/slave/serial-power-manager.c

diff --git a/Documentation/devicetree/bindings/uart_slave/wi2wi,w2cbw003.txt b/Documentation/devicetree/bindings/uart_slave/wi2wi,w2cbw003.txt
new file mode 100644
index 000000000000..cfe6ee5e01e9
--- /dev/null
+++ b/Documentation/devicetree/bindings/uart_slave/wi2wi,w2cbw003.txt
@@ -0,0 +1,19 @@
+wi2wi bluetooth module
+
+This is accessed via a serial port and is largely controlled via that
+link.  Extra configuration is needed to enable power on/off
+
+Required properties:
+- compatible: "wi2wi,w2cbw003"
+- vdd-supply: regulator used to power the device.
+
+The node for this device must be the child of a UART.
+
+Example:
+
+&uart1 {
+       bluetooth {
+               compatible = "wi2wi,w2cbw003";
+               vdd-supply = <&vaux4>;
+       };
+};
diff --git a/Documentation/devicetree/bindings/uart_slave/wi2wi,w2sg0004.txt b/Documentation/devicetree/bindings/uart_slave/wi2wi,w2sg0004.txt
new file mode 100644
index 000000000000..6bcf3006c1a4
--- /dev/null
+++ b/Documentation/devicetree/bindings/uart_slave/wi2wi,w2sg0004.txt
@@ -0,0 +1,37 @@
+wi2wi GPS device
+
+This is accessed via a serial port and is largely controlled via that
+link.  Extra configuration is needed to enable power on/off
+
+Required properties:
+- compatible: "wi2wi,w2sg0004"
+- gpios: gpio used to toggle 'on/off' pin
+- interrupts: interrupt generated by RX pin when device
+      should be off
+
+Optional properties:
+- vdd-supply: regulator used to power antenna
+- pinctrl: "default", "off"
+      if "off" setting is provided it is imposed when device should
+      be off.  This can route the RX pin to a GPIO interrupt.
+
+The w2sg0004 uses a pin-toggle both to power-on and to
+power-off, so the driver needs to detect what state it is in.
+It does this by detecting characters on the RX line.
+When it should be off, these can optionally be detected by a GPIO.
+
+The node for this device must be the child of a UART.
+
+Example:
+&uart2 {
+       gps {
+               compatible = "wi2iw,w2sg0004";
+               vdd-supply = <&vsim>;
+               gpios = <&gpio5 17 0>; /* GPIO_145 */
+               interrupts-extended = <&gpio5 19 0>; /* GPIO_147 */
+               /* When off, switch RX to be an interrupt */
+               pinctrl-names = "default", "off";
+               pinctrl-0 = <&uart2_pins>;
+               pinctrl-1 = <&uart2_pins_rx_gpio>;
+       };
+};
diff --git a/Documentation/devicetree/bindings/vendor-prefixes.txt b/Documentation/devicetree/bindings/vendor-prefixes.txt
index 80339192c93e..45c703a3b29d 100644
--- a/Documentation/devicetree/bindings/vendor-prefixes.txt
+++ b/Documentation/devicetree/bindings/vendor-prefixes.txt
@@ -202,6 +202,7 @@ variscite	Variscite Ltd.
 via	VIA Technologies, Inc.
 virtio	Virtual I/O Device Specification, developed by the OASIS consortium
 voipac	Voipac Technologies s.r.o.
+wi2wi	wi2wi Inc.  http://www.wi2wi.com/
 winbond Winbond Electronics corp.
 wlf	Wolfson Microelectronics
 wm	Wondermedia Technologies, Inc.
diff --git a/drivers/tty/serial/slave/Kconfig b/drivers/tty/serial/slave/Kconfig
index 6620e78b763e..46285d8895b7 100644
--- a/drivers/tty/serial/slave/Kconfig
+++ b/drivers/tty/serial/slave/Kconfig
@@ -4,3 +4,18 @@ menuconfig UART_SLAVE
 	help
 	 Devices which attach via a uart, but need extra
 	 driver support for power management etc.
+
+if UART_SLAVE
+
+config SERIAL_POWER_MANAGER
+	tristate "Power Management controller for serial-attached devices"
+	default n
+	help
+	 Some devices permanently attached via a UART can benefit from
+	 being power-managed when the tty device is opened or closed.
+	 This driver can support several such devices with simple
+	 power requirements such as enabling a regulator.
+
+	 If in doubt, say 'N'
+
+endif
diff --git a/drivers/tty/serial/slave/Makefile b/drivers/tty/serial/slave/Makefile
index aac8697fa406..5d9b3d373138 100644
--- a/drivers/tty/serial/slave/Makefile
+++ b/drivers/tty/serial/slave/Makefile
@@ -1,2 +1,3 @@
 
 obj-$(CONFIG_UART_SLAVE) += uart_slave_core.o
+obj-$(CONFIG_SERIAL_POWER_MANAGER) += serial-power-manager.o
diff --git a/drivers/tty/serial/slave/serial-power-manager.c b/drivers/tty/serial/slave/serial-power-manager.c
new file mode 100644
index 000000000000..81b8f909fd3a
--- /dev/null
+++ b/drivers/tty/serial/slave/serial-power-manager.c
@@ -0,0 +1,510 @@
+/*
+ * Serial-power-manager
+ * uart-slave device that intercepts open/close events on the tty,
+ * and turns power on/off for the device which is connected.
+ *
+ * Currently supported devices:
+ *  wi2wi,w2sg0004 - GPS with on/off toggle on a GPIO
+ *  wi2wi,w2cbw003 - bluetooth port; powered by regulator.
+ *
+ * When appropriate, an RFKILL will be registered which
+ * can power-down the device even when it is open.
+ *
+ * Device can be turned on either by
+ *  - enabling a regulator.  Disable to turn off
+ *  - toggling a GPIO.  Toggle again to turn off.  This requires
+ *     that we know the current state.  It is assumed to be 'off'
+ *     at boot, however if an interrupt can be generated when on,
+ *     such as by connecting RX to a GPIO, that can be used to detect
+ *     if the device is on when it should be off.
+ */
+
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/err.h>
+#include <linux/regulator/consumer.h>
+#include <linux/platform_device.h>
+#include <linux/of_device.h>
+#include <linux/tty.h>
+#include <linux/gpio.h>
+#include <linux/of_gpio.h>
+#include <linux/of_irq.h>
+#include <linux/interrupt.h>
+#include <linux/delay.h>
+#include <linux/rfkill.h>
+
+#include <linux/uart_slave.h>
+
+/* This is used for testing. Setting this module parameter
+ * will simulate booting with the device "on"
+ */
+static bool toggle_on_probe = false;
+module_param(toggle_on_probe, bool, 0);
+MODULE_PARM_DESC(toggle_on_probe, "simulate power-on with devices active");
+
+struct spm_config {
+	int	rfkill_type;		/* type of rfkill to register */
+	int	toggle_time;		/* msec to pulse GPIO for on/off */
+	int	toggle_gap;		/* minimum msecs between toggles */
+	bool	off_in_suspend;
+}
+	simple_config = {
+		.off_in_suspend = true,
+	},
+	w2sg_config = {
+		.rfkill_type = RFKILL_TYPE_GPS,
+		.toggle_time = 10,
+		.toggle_gap = 500,
+		.off_in_suspend = true,
+	};
+
+const static struct of_device_id spm_dt_ids[] = {
+       { .compatible = "wi2wi,w2sg0004", .data = &w2sg_config},
+       { .compatible = "wi2wi,w2cbw003", .data = &simple_config},
+       {}
+};
+
+struct spm_data {
+	const struct spm_config *config;
+	struct gpio_desc *gpiod;
+	int		irq;	/* irq line from RX pin when pinctrl
+				 * set to 'idle' */
+	struct regulator *reg;
+
+	unsigned long	toggle_time;
+	unsigned long	toggle_gap;
+	unsigned long	last_toggle;	/* jiffies when last toggle completed. */
+	unsigned long	backoff;	/* jiffies since last_toggle when
+					 * we try again
+					 */
+	enum {Idle, Down, Up} state;	/* state-machine state. */
+
+	int		open_cnt;
+	bool		requested, is_on;
+	bool		suspended;
+	bool		reg_enabled;
+
+	struct pinctrl	*pins;
+	struct pinctrl_state *pins_off;
+
+	struct delayed_work work;
+	spinlock_t	lock;
+	struct device	*dev;
+
+	struct rfkill	*rfkill;
+
+	int (*old_open)(struct tty_struct * tty, struct file * filp);
+	void (*old_close)(struct tty_struct * tty, struct file * filp);
+
+};
+
+/* When a device is powered on/off by toggling a GPIO we perform
+ * all the toggling via a workqueue to ensure only one toggle happens
+ * at a time and to allow easy timing.
+ * This is managed as a state machine which transitions
+ *  Idle -> Down -> Up -> Idle
+ * The GPIO is held down for toggle_time and then up for toggle_time,
+ * and then we assume the device has changed state.
+ * We never toggle until at least toggle_gap has passed since the
+ * last toggle.
+ */
+static void toggle_work(struct work_struct *work)
+{
+	struct spm_data *data = container_of(
+		work, struct spm_data, work.work);
+
+	if (data->gpiod == NULL)
+		return;
+
+	spin_lock_irq(&data->lock);
+	switch (data->state) {
+	case Up:
+		data->state = Idle;
+		if (data->requested == data->is_on)
+			break;
+		if (!data->requested)
+			/* Assume it is off unless activity is detected */
+			break;
+		/* Try again in a while unless we get some activity */
+		dev_dbg(data->dev, "Wait %dusec until retry\n",
+			jiffies_to_msecs(data->backoff));
+		schedule_delayed_work(&data->work, data->backoff);
+		break;
+	case Idle:
+		if (data->requested == data->is_on)
+			break;
+
+		/* Time to toggle */
+		dev_dbg(data->dev, "Starting toggle to turn %s\n",
+			data->requested ? "on" : "off");
+		data->state = Down;
+		spin_unlock_irq(&data->lock);
+		gpiod_set_value_cansleep(data->gpiod, 1);
+		schedule_delayed_work(&data->work, data->toggle_time);
+
+		return;
+
+	case Down:
+		data->state = Up;
+		data->last_toggle = jiffies;
+		dev_dbg(data->dev, "Toggle completed, should be %s now.\n",
+			data->is_on ? "off" : "on");
+		data->is_on = ! data->is_on;
+		spin_unlock_irq(&data->lock);
+
+		gpiod_set_value_cansleep(data->gpiod, 0);
+		schedule_delayed_work(&data->work, data->toggle_time);
+
+		return;
+	}
+	spin_unlock_irq(&data->lock);
+}
+
+static irqreturn_t spm_isr(int irq, void *dev_id)
+{
+	struct spm_data *data = dev_id;
+	unsigned long flags;
+
+	spin_lock_irqsave(&data->lock, flags);
+	if (!data->requested && !data->is_on && data->state == Idle &&
+	    time_after(jiffies, data->last_toggle + data->backoff)) {
+		data->is_on = 1;
+		data->backoff *= 2;
+		dev_dbg(data->dev, "Received data, must be on. Try to turn off\n");
+		if (!data->suspended)
+			schedule_delayed_work(&data->work, 0);
+	}
+	spin_unlock_irqrestore(&data->lock, flags);
+	return IRQ_HANDLED;
+}
+
+static void spm_on(struct spm_data *data)
+{
+	if (!data->rfkill || !rfkill_blocked(data->rfkill)) {
+		unsigned long flags;
+
+		if (!data->reg_enabled &&
+		    data->reg &&
+		    regulator_enable(data->reg) == 0)
+			data->reg_enabled = true;
+
+		spin_lock_irqsave(&data->lock, flags);
+		if (!data->requested) {
+			dev_dbg(data->dev, "TTY open - turn device on\n");
+			data->requested = true;
+			data->backoff = data->toggle_gap;
+			if (data->irq > 0) {
+				disable_irq(data->irq);
+				pinctrl_pm_select_default_state(data->dev);
+			}
+			if (!data->suspended && data->state == Idle)
+				schedule_delayed_work(&data->work, 0);
+		}
+		spin_unlock_irqrestore(&data->lock, flags);
+	}
+}
+
+static int spm_open(struct tty_struct *tty, struct file *filp)
+{
+	struct spm_data *data = dev_get_drvdata(tty->dev->parent);
+
+	data->open_cnt++;
+	spm_on(data);
+	if (data->old_open)
+		return data->old_open(tty, filp);
+	return -ENODEV;
+}
+
+static void spm_off(struct spm_data *data)
+{
+	unsigned long flags;
+
+	if (data->reg && data->reg_enabled)
+		if (regulator_disable(data->reg) == 0)
+			data->reg_enabled = false;
+
+	spin_lock_irqsave(&data->lock, flags);
+	if (data->requested) {
+		data->requested = false;
+		data->backoff = data->toggle_gap;
+		if (data->pins_off) {
+			pinctrl_select_state(data->pins,
+					     data->pins_off);
+			enable_irq(data->irq);
+		}
+		if (!data->suspended && data->state == Idle)
+			schedule_delayed_work(&data->work, 0);
+	}
+	spin_unlock_irqrestore(&data->lock, flags);
+}
+
+static void spm_close(struct tty_struct *tty, struct file *filp)
+{
+	struct spm_data *data = dev_get_drvdata(tty->dev->parent);
+
+	data->open_cnt--;
+	if (!data->open_cnt) {
+		dev_dbg(data->dev, "TTY closed - turn device off\n");
+		spm_off(data);
+	}
+
+	if (data->old_close)
+		data->old_close(tty, filp);
+}
+
+static int spm_rfkill_set_block(void *vdata, bool blocked)
+{
+	struct spm_data *data = vdata;
+
+	dev_dbg(data->dev, "rfkill_set_blocked %d\n", blocked);
+	if (blocked)
+		spm_off(data);
+
+	if (!blocked &&
+	    data->open_cnt)
+		spm_on(data);
+
+	return 0;
+}
+
+static struct rfkill_ops spm_rfkill_ops = {
+	.set_block = spm_rfkill_set_block,
+};
+
+static int spm_suspend(struct device *dev)
+{
+	/* Ignore incoming data and just turn device off.
+	 * we cannot really wait for a separate thread to
+	 * do things, so we disable that and do it all
+	 * here
+	 */
+	struct spm_data *data = dev_get_drvdata(dev);
+
+	spin_lock_irq(&data->lock);
+	data->suspended = true;
+	spin_unlock_irq(&data->lock);
+	if (!data->config->off_in_suspend)
+		return 0;
+
+	if (data->gpiod) {
+
+		cancel_delayed_work_sync(&data->work);
+		if (data->state == Down) {
+			dev_dbg(data->dev, "Suspending while GPIO down - raising\n");
+			msleep(data->config->toggle_time);
+			gpiod_set_value_cansleep(data->gpiod, 0);
+			data->last_toggle = jiffies;
+			data->is_on = !data->is_on;
+			data->state = Up;
+		}
+		if (data->state == Up) {
+			msleep(data->config->toggle_time);
+			data->state = Idle;
+		}
+		if (data->is_on) {
+			dev_dbg(data->dev, "Suspending while device on: toggling\n");
+			gpiod_set_value_cansleep(data->gpiod, 1);
+			msleep(data->config->toggle_time);
+			gpiod_set_value_cansleep(data->gpiod, 0);
+			data->is_on = 0;
+		}
+	}
+
+	if (data->reg && data->reg_enabled)
+		if (regulator_disable(data->reg) == 0)
+			data->reg_enabled = false;
+
+	return 0;
+}
+
+static int spm_resume(struct device *dev)
+{
+	struct spm_data *data = dev_get_drvdata(dev);
+
+	spin_lock_irq(&data->lock);
+	data->suspended = false;
+	spin_unlock_irq(&data->lock);
+	schedule_delayed_work(&data->work, 0);
+
+	if (data->open_cnt &&
+	    (!data->rfkill || !rfkill_blocked(data->rfkill))) {
+		if (!data->reg_enabled &&
+		    data->reg &&
+		    regulator_enable(data->reg) == 0)
+			data->reg_enabled = true;
+	}
+	return 0;
+}
+
+static const struct dev_pm_ops spm_pm_ops = {
+	SET_SYSTEM_SLEEP_PM_OPS(spm_suspend, spm_resume)
+};
+
+static int spm_probe(struct device *dev)
+{
+	struct uart_slave *slave = container_of(dev, struct uart_slave, dev);
+	struct spm_data *data;
+	struct regulator *reg;
+	int err;
+	const struct of_device_id *id;
+	const char *name;
+
+	if (dev->parent == NULL)
+		return -ENODEV;
+
+	id = of_match_device(spm_dt_ids, dev);
+	if (!id)
+		return -ENODEV;
+
+	if (dev->of_node && dev->of_node->name)
+		name = dev->of_node->name;
+	else
+		name = "serial-power-manager";
+
+	data = devm_kzalloc(dev, sizeof(*data), GFP_KERNEL);
+	if (!data)
+		return -ENOMEM;
+
+	data->config = id->data;
+	data->toggle_time = msecs_to_jiffies(data->config->toggle_time) + 1;
+	data->toggle_gap = msecs_to_jiffies(data->config->toggle_gap) + 1;
+	data->last_toggle = jiffies;
+	data->backoff = data->toggle_gap;
+	data->state = Idle;
+	spin_lock_init(&data->lock);
+	INIT_DELAYED_WORK(&data->work, toggle_work);
+
+	/* If a regulator is provided, it is enabled on 'open'
+	 * and disabled on 'release'
+	 */
+	reg = devm_regulator_get(dev, "vdd");
+	if (IS_ERR(reg)) {
+		err = PTR_ERR(reg);
+		if (err != -ENODEV)
+			goto out;
+	} else
+		data->reg = reg;
+
+	/* If an irq is provided, any transitions are taken as
+	 * indication that the device is currently "on"
+	 */
+	data->irq = of_irq_get(dev->of_node, 0);
+	if (data->irq < 0) {
+		err = data->irq;
+		if (err != -EINVAL)
+			goto out;
+	} else {
+		dev_dbg(dev, "IRQ configured: %d\n", data->irq);
+
+		irq_set_status_flags(data->irq, IRQ_NOAUTOEN);
+		err = devm_request_irq(dev, data->irq, spm_isr,
+				       IRQF_TRIGGER_FALLING,
+				       name, data);
+
+		if (err)
+			goto out;
+
+	}
+
+	/* If a gpio is provided, then it is used to turn the device
+	 * on/off.
+	 * The GPIO is toggled to change the state of the device.
+	 * A "toggle" involves holding the GPIO active for toggle_time.
+	 */
+	data->gpiod = devm_gpiod_get(dev, NULL, GPIOD_OUT_LOW);
+	if (IS_ERR(data->gpiod)) {
+		err = PTR_ERR(data->gpiod);
+		if (err != -ENOENT)
+			goto out;
+		data->gpiod = NULL;
+	} else
+		dev_dbg(dev, "GPIO configured: %d\n",
+			desc_to_gpio(data->gpiod));
+
+	/* If an 'off' pinctrl state is defined, we apply that
+	 * when the device is assumed to be off.  This is expected to
+	 * route the 'rx' line to the 'irq' interrupt.
+	 */
+	data->pins = devm_pinctrl_get(dev);
+	if (data->pins && data->irq > 0) {
+		data->pins_off = pinctrl_lookup_state(data->pins, "off");
+		if (IS_ERR(data->pins_off))
+			data->pins_off = NULL;
+	}
+
+	if (data->config->rfkill_type) {
+		data->rfkill = rfkill_alloc(name, dev,
+					    data->config->rfkill_type,
+					    &spm_rfkill_ops, data);
+		if (!data->rfkill) {
+			err = -ENOMEM;
+			goto out;
+		}
+		err = rfkill_register(data->rfkill);
+		if (err) {
+			dev_err(dev, "Cannot register rfkill device");
+			rfkill_destroy(data->rfkill);
+			goto out;
+		}
+	}
+	dev_set_drvdata(dev, data);
+	data->dev = dev;
+	data->old_open = slave->ops.open;
+	data->old_close = slave->ops.close;
+	slave->ops.open = spm_open;
+	slave->ops.close = spm_close;
+	uart_slave_add_tty(slave);
+
+	if (data->pins_off)
+		pinctrl_select_state(data->pins, data->pins_off);
+	if (data->irq > 0)
+		enable_irq(data->irq);
+
+	if (toggle_on_probe && data->gpiod) {
+		dev_dbg(data->dev, "Performing initial toggle\n");
+		gpiod_set_value_cansleep(data->gpiod, 1);
+		msleep(data->config->toggle_time);
+		gpiod_set_value_cansleep(data->gpiod, 0);
+		msleep(data->config->toggle_time);
+	}
+	err = 0;
+out:
+	dev_dbg(data->dev, "Probed: err=%d\n", err);
+	return err;
+}
+
+static int spm_remove(struct device *dev)
+{
+       struct spm_data *data = dev_get_drvdata(dev);
+
+       if (data->rfkill) {
+               rfkill_unregister(data->rfkill);
+               rfkill_destroy(data->rfkill);
+       }
+       return 0;
+}
+
+static struct device_driver spm_driver = {
+	.name		= "serial-power-manager",
+	.owner		= THIS_MODULE,
+	.of_match_table	= spm_dt_ids,
+	.probe		= spm_probe,
+	.remove		= spm_remove,
+};
+
+static int __init spm_init(void)
+{
+       return uart_slave_driver_register(&spm_driver);
+}
+module_init(spm_init);
+
+static void __exit spm_exit(void)
+{
+	driver_unregister(&spm_driver);
+}
+module_exit(spm_exit);
+
+MODULE_AUTHOR("NeilBrown <neil@xxxxxxxxxx>");
+MODULE_DEVICE_TABLE(of, spm_dt_ids);
+MODULE_DESCRIPTION("Power management for Serial-attached device.");
+MODULE_LICENSE("GPL v2");


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