[PATCH v5 3/5] misc serdev: Add w2sg0004 (gps receiver) power control driver

[H. Nikolaus Schaller]

Add driver for Wi2Wi W2SG0004/84 GPS module connected to some SoC UART.

It uses serdev API hooks to monitor and forward the UART traffic to /dev/ttyGPSn
and turn on/off the module. It also detects if the module is turned on (sends data)
but should be off, e.g. if it was already turned on during boot or power-on-reset.

Additionally, rfkill block/unblock can be used to control an external LNA
(and power down the module if not needed).

The driver concept is based on code developed by Neil Brown <neilb@xxxxxxx>
but simplified and adapted to use the new serdev API introduced in v4.11.

Signed-off-by: H. Nikolaus Schaller <hns@xxxxxxxxxxxxx>
---
 drivers/misc/Kconfig    |  10 +
 drivers/misc/Makefile   |   1 +
 drivers/misc/w2sg0004.c | 553 ++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 564 insertions(+)
 create mode 100644 drivers/misc/w2sg0004.c

diff --git a/drivers/misc/Kconfig b/drivers/misc/Kconfig
index f1a5c2357b14..a3b11016ed2b 100644
--- a/drivers/misc/Kconfig
+++ b/drivers/misc/Kconfig
@@ -508,4 +508,14 @@ source "drivers/misc/mic/Kconfig"
 source "drivers/misc/genwqe/Kconfig"
 source "drivers/misc/echo/Kconfig"
 source "drivers/misc/cxl/Kconfig"
+
+config W2SG0004
+	tristate "W2SG00x4 on/off control"
+	depends on GPIOLIB && SERIAL_DEV_BUS
+	help
+          Enable on/off control of W2SG00x4 GPS moduled connected
+	  to some SoC UART to allow powering up/down if the /dev/ttyGPSn
+	  is opened/closed.
+	  It also provides a rfkill gps name to control the LNA power.
+
 endmenu
diff --git a/drivers/misc/Makefile b/drivers/misc/Makefile
index 5ca5f64df478..d9d824b3d20a 100644
--- a/drivers/misc/Makefile
+++ b/drivers/misc/Makefile
@@ -50,6 +50,7 @@ obj-$(CONFIG_SRAM_EXEC)		+= sram-exec.o
 obj-y				+= mic/
 obj-$(CONFIG_GENWQE)		+= genwqe/
 obj-$(CONFIG_ECHO)		+= echo/
+obj-$(CONFIG_W2SG0004)		+= w2sg0004.o
 obj-$(CONFIG_VEXPRESS_SYSCFG)	+= vexpress-syscfg.o
 obj-$(CONFIG_CXL_BASE)		+= cxl/
 obj-$(CONFIG_ASPEED_LPC_CTRL)	+= aspeed-lpc-ctrl.o
diff --git a/drivers/misc/w2sg0004.c b/drivers/misc/w2sg0004.c
new file mode 100644
index 000000000000..6bfd12eb8e02
--- /dev/null
+++ b/drivers/misc/w2sg0004.c
@@ -0,0 +1,553 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Driver for power controlling the w2sg0004/w2sg0084 GPS receiver.
+ *
+ * Copyright (C) 2013 Neil Brown <neilb@xxxxxxx>
+ * Copyright (C) 2015-2017 H. Nikolaus Schaller <hns@xxxxxxxxxxxxx>,
+ *						Golden Delicious Computers
+ *
+ * This receiver has an ON/OFF pin which must be toggled to
+ * turn the device 'on' of 'off'.  A high->low->high toggle
+ * will switch the device on if it is off, and off if it is on.
+ *
+ * To enable receiving on/off requests we register with the
+ * UART power management notifications.
+ *
+ * It is not possible to directly detect the state of the device.
+ * However when it is on it will send characters on a UART line
+ * regularly.
+ *
+ * To detect that the power state is out of sync (e.g. if GPS
+ * was enabled before a reboot), we register for UART data received
+ * notifications.
+ *
+ * In addition we register as a rfkill client so that we can
+ * control the LNA power.
+ *
+ */
+
+#include <linux/delay.h>
+#include <linux/err.h>
+#include <linux/interrupt.h>
+#include <linux/irq.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/of_irq.h>
+#include <linux/of_gpio.h>
+#include <linux/platform_device.h>
+#include <linux/regulator/consumer.h>
+#include <linux/rfkill.h>
+#include <linux/serdev.h>
+#include <linux/sched.h>
+#include <linux/slab.h>
+#include <linux/tty.h>
+#include <linux/tty_flip.h>
+#include <linux/workqueue.h>
+
+/*
+ * There seems to be restrictions on how quickly we can toggle the
+ * on/off line.  data sheets says "two rtc ticks", whatever that means.
+ * If we do it too soon it doesn't work.
+ * So we have a state machine which uses the common work queue to ensure
+ * clean transitions.
+ * When a change is requested we record that request and only act on it
+ * once the previous change has completed.
+ * A change involves a 10ms low pulse, and a 990ms raised level, so only
+ * one change per second.
+ */
+
+enum w2sg_state {
+	W2SG_IDLE,	/* is not changing state */
+	W2SG_PULSE,	/* activate on/off impulse */
+	W2SG_NOPULSE	/* deactivate on/off impulse */
+};
+
+struct w2sg_data {
+	struct		rfkill *rf_kill;
+	struct		regulator *lna_regulator;
+	int		lna_blocked;	/* rfkill block gps active */
+	int		lna_is_off;	/* LNA is currently off */
+	int		is_on;		/* current state (0/1) */
+	unsigned long	last_toggle;
+	unsigned long	backoff;	/* time to wait since last_toggle */
+	int		on_off_gpio;	/* the on-off gpio number */
+	struct		serdev_device *uart;	/* uart connected to the chip */
+	struct		tty_driver *tty_drv;	/* this is the user space tty */
+	struct		device *dev;	/* from tty_port_register_device() */
+	struct		tty_port port;
+	int		open_count;	/* how often we were opened */
+	enum		w2sg_state state;
+	int		requested;	/* requested state (0/1) */
+	int		suspended;
+	struct delayed_work work;
+	int		discard_count;
+};
+
+/* should become w2sg_by_minor[n] if we want to support multiple devices */
+static struct w2sg_data *w2sg_by_minor;
+
+static int w2sg_set_lna_power(struct w2sg_data *data)
+{
+	int ret = 0;
+	int off = data->suspended || !data->requested || data->lna_blocked;
+
+	pr_debug("%s: %s\n", __func__, off ? "off" : "on");
+
+	if (off != data->lna_is_off) {
+		data->lna_is_off = off;
+		if (!IS_ERR_OR_NULL(data->lna_regulator)) {
+			if (off)
+				regulator_disable(data->lna_regulator);
+			else
+				ret = regulator_enable(data->lna_regulator);
+		}
+	}
+
+	return ret;
+}
+
+static void w2sg_set_power(void *pdata, int val)
+{
+	struct w2sg_data *data = (struct w2sg_data *) pdata;
+
+	pr_debug("%s to state=%d (requested=%d)\n", __func__, val,
+		 data->requested);
+
+	if (val && !data->requested) {
+		data->requested = true;
+	} else if (!val && data->requested) {
+		data->backoff = HZ;
+		data->requested = false;
+	} else
+		return;
+
+	if (!data->suspended)
+		schedule_delayed_work(&data->work, 0);
+}
+
+/* called each time data is received by the UART (i.e. sent by the w2sg0004) */
+static int w2sg_uart_receive_buf(struct serdev_device *serdev,
+				const unsigned char *rxdata,
+				size_t count)
+{
+	struct w2sg_data *data =
+		(struct w2sg_data *) serdev_device_get_drvdata(serdev);
+
+	if (!data->requested && !data->is_on) {
+		/*
+		 * we have received characters while the w2sg
+		 * should have been be turned off
+		 */
+		data->discard_count += count;
+		if ((data->state == W2SG_IDLE) &&
+		    time_after(jiffies,
+		    data->last_toggle + data->backoff)) {
+			/* Should be off by now, time to toggle again */
+			pr_debug("w2sg00x4 has sent %d characters data although it should be off!\n",
+				data->discard_count);
+
+			data->discard_count = 0;
+
+			data->is_on = true;
+			data->backoff *= 2;
+			if (!data->suspended)
+				schedule_delayed_work(&data->work, 0);
+		}
+	} else if (data->open_count > 0) {
+		int n;
+
+		pr_debug("w2sg00x4: push %lu chars to tty port\n",
+			(unsigned long) count);
+
+		/* pass to user-space */
+		n = tty_insert_flip_string(&data->port, rxdata, count);
+		if (n != count)
+			pr_err("w2sg00x4: did loose %lu characters\n",
+				(unsigned long) (count - n));
+		tty_flip_buffer_push(&data->port);
+		return n;
+	}
+
+	/* assume we have processed everything */
+	return count;
+}
+
+/* try to toggle the power state by sending a pulse to the on-off GPIO */
+static void toggle_work(struct work_struct *work)
+{
+	struct w2sg_data *data = container_of(work, struct w2sg_data,
+					      work.work);
+
+	switch (data->state) {
+	case W2SG_IDLE:
+		if (data->requested == data->is_on)
+			return;
+
+		w2sg_set_lna_power(data);	/* update LNA power state */
+		gpio_set_value_cansleep(data->on_off_gpio, 0);
+		data->state = W2SG_PULSE;
+
+		pr_debug("w2sg: power gpio ON\n");
+
+		schedule_delayed_work(&data->work,
+				      msecs_to_jiffies(10));
+		break;
+
+	case W2SG_PULSE:
+		gpio_set_value_cansleep(data->on_off_gpio, 1);
+		data->last_toggle = jiffies;
+		data->state = W2SG_NOPULSE;
+		data->is_on = !data->is_on;
+
+		pr_debug("w2sg: power gpio OFF\n");
+
+		schedule_delayed_work(&data->work,
+				      msecs_to_jiffies(10));
+		break;
+
+	case W2SG_NOPULSE:
+		data->state = W2SG_IDLE;
+
+		pr_debug("w2sg: idle\n");
+
+		break;
+
+	}
+}
+
+static int w2sg_rfkill_set_block(void *pdata, bool blocked)
+{
+	struct w2sg_data *data = pdata;
+
+	pr_debug("%s: blocked: %d\n", __func__, blocked);
+
+	data->lna_blocked = blocked;
+
+	return w2sg_set_lna_power(data);
+}
+
+static struct rfkill_ops w2sg0004_rfkill_ops = {
+	.set_block = w2sg_rfkill_set_block,
+};
+
+static struct serdev_device_ops serdev_ops = {
+	.receive_buf = w2sg_uart_receive_buf,
+};
+
+/*
+ * we are a man-in the middle between the user-space visible tty port
+ * and the serdev tty where the chip is connected.
+ * This allows us to recognise when the device should be powered on
+ * or off and handle the "false" state that data arrives while no
+ * users-space tty client exists.
+ */
+
+static struct w2sg_data *w2sg_get_by_minor(unsigned int minor)
+{
+	BUG_ON(minor >= 1);
+	return w2sg_by_minor;
+}
+
+static int w2sg_tty_install(struct tty_driver *driver, struct tty_struct *tty)
+{
+	struct w2sg_data *data;
+	int retval;
+
+	pr_debug("%s() tty = %p\n", __func__, tty);
+
+	data = w2sg_get_by_minor(tty->index);
+
+	if (!data)
+		return -ENODEV;
+
+	retval = tty_standard_install(driver, tty);
+	if (retval)
+		goto error_init_termios;
+
+	tty->driver_data = data;
+
+	return 0;
+
+error_init_termios:
+	tty_port_put(&data->port);
+	return retval;
+}
+
+static int w2sg_tty_open(struct tty_struct *tty, struct file *file)
+{
+	struct w2sg_data *data = tty->driver_data;
+
+	pr_debug("%s() data = %p open_count = ++%d\n", __func__,
+		 data, data->open_count);
+
+	w2sg_set_power(data, ++data->open_count > 0);
+
+	return tty_port_open(&data->port, tty, file);
+}
+
+static void w2sg_tty_close(struct tty_struct *tty, struct file *file)
+{
+	struct w2sg_data *data = tty->driver_data;
+
+	pr_debug("%s()\n", __func__);
+
+	w2sg_set_power(data, --data->open_count > 0);
+
+	tty_port_close(&data->port, tty, file);
+}
+
+static int w2sg_tty_write(struct tty_struct *tty,
+		const unsigned char *buffer, int count)
+{
+	struct w2sg_data *data = tty->driver_data;
+
+	/* simply pass down to UART */
+	return serdev_device_write_buf(data->uart, buffer, count);
+}
+
+static const struct tty_operations w2sg_serial_ops = {
+	.install = w2sg_tty_install,
+	.open = w2sg_tty_open,
+	.close = w2sg_tty_close,
+	.write = w2sg_tty_write,
+};
+
+static const struct tty_port_operations w2sg_port_ops = {
+	/* none defined, but we need the struct */
+};
+
+static int w2sg_probe(struct serdev_device *serdev)
+{
+	struct w2sg_data *data;
+	struct rfkill *rf_kill;
+	int err;
+	int minor;
+	enum of_gpio_flags flags;
+
+	pr_debug("%s()\n", __func__);
+
+	/*
+	 * For future consideration:
+	 * for multiple such GPS receivers in one system
+	 * we need a mechanism to define distinct minor values
+	 * and search for an unused one.
+	 */
+	minor = 0;
+	if (w2sg_get_by_minor(minor)) {
+		pr_err("w2sg minor is already in use!\n");
+		return -ENODEV;
+	}
+
+	data = devm_kzalloc(&serdev->dev, sizeof(*data), GFP_KERNEL);
+	if (data == NULL)
+		return -ENOMEM;
+
+	serdev_device_set_drvdata(serdev, data);
+
+	data->on_off_gpio = of_get_named_gpio_flags(serdev->dev.of_node,
+						     "enable-gpios", 0,
+						     &flags);
+	/* defer until we have all gpios */
+	if (data->on_off_gpio == -EPROBE_DEFER)
+		return -EPROBE_DEFER;
+
+	data->lna_regulator = devm_regulator_get_optional(&serdev->dev,
+							"lna");
+	if (IS_ERR(data->lna_regulator)) {
+		/* defer until we can get the regulator */
+		if (PTR_ERR(data->lna_regulator) == -EPROBE_DEFER)
+			return -EPROBE_DEFER;
+
+		data->lna_regulator = NULL;
+	}
+	pr_debug("%s() lna_regulator = %p\n", __func__, data->lna_regulator);
+
+	data->lna_blocked = true;
+	data->lna_is_off = true;
+
+	data->is_on = false;
+	data->requested = false;
+	data->state = W2SG_IDLE;
+	data->last_toggle = jiffies;
+	data->backoff = HZ;
+
+	data->uart = serdev;
+
+	INIT_DELAYED_WORK(&data->work, toggle_work);
+
+	err = devm_gpio_request(&serdev->dev, data->on_off_gpio,
+				"w2sg0004-on-off");
+	if (err < 0)
+		goto out;
+
+	gpio_direction_output(data->on_off_gpio, false);
+
+	serdev_device_set_client_ops(data->uart, &serdev_ops);
+	serdev_device_open(data->uart);
+
+	serdev_device_set_baudrate(data->uart, 9600);
+	serdev_device_set_flow_control(data->uart, false);
+
+	rf_kill = rfkill_alloc("GPS", &serdev->dev, RFKILL_TYPE_GPS,
+				&w2sg0004_rfkill_ops, data);
+	if (rf_kill == NULL) {
+		err = -ENOMEM;
+		goto err_rfkill;
+	}
+
+	err = rfkill_register(rf_kill);
+	if (err) {
+		dev_err(&serdev->dev, "Cannot register rfkill device\n");
+		goto err_rfkill;
+	}
+
+	data->rf_kill = rf_kill;
+
+	/* allocate the tty driver */
+	data->tty_drv = alloc_tty_driver(1);
+	if (!data->tty_drv)
+		return -ENOMEM;
+
+	/* initialize the tty driver */
+	data->tty_drv->owner = THIS_MODULE;
+	data->tty_drv->driver_name = "w2sg0004";
+	data->tty_drv->name = "ttyGPS";
+	data->tty_drv->major = 0;
+	data->tty_drv->minor_start = 0;
+	data->tty_drv->type = TTY_DRIVER_TYPE_SERIAL;
+	data->tty_drv->subtype = SERIAL_TYPE_NORMAL;
+	data->tty_drv->flags = TTY_DRIVER_REAL_RAW | TTY_DRIVER_DYNAMIC_DEV;
+	data->tty_drv->init_termios = tty_std_termios;
+	data->tty_drv->init_termios.c_cflag = B9600 | CS8 | CREAD |
+					      HUPCL | CLOCAL;
+	/*
+	 * optional:
+	 * tty_termios_encode_baud_rate(&data->tty_drv->init_termios,
+					115200, 115200);
+	 * w2sg_tty_termios(&data->tty_drv->init_termios);
+	 */
+	tty_set_operations(data->tty_drv, &w2sg_serial_ops);
+
+	/* register the tty driver */
+	err = tty_register_driver(data->tty_drv);
+	if (err) {
+		pr_err("%s - tty_register_driver failed(%d)\n",
+			__func__, err);
+		put_tty_driver(data->tty_drv);
+		goto err_rfkill;
+	}
+
+	/* minor (0) is now in use */
+	w2sg_by_minor = data;
+
+	tty_port_init(&data->port);
+	data->port.ops = &w2sg_port_ops;
+
+	data->dev = tty_port_register_device(&data->port,
+			data->tty_drv, minor, &serdev->dev);
+
+	/* keep off until user space requests the device */
+	w2sg_set_power(data, false);
+
+	return 0;
+
+err_rfkill:
+	rfkill_destroy(rf_kill);
+	serdev_device_close(data->uart);
+out:
+	return err;
+}
+
+static void w2sg_remove(struct serdev_device *serdev)
+{
+	struct w2sg_data *data = serdev_device_get_drvdata(serdev);
+	int minor;
+
+	cancel_delayed_work_sync(&data->work);
+
+	/* what is the right sequence to avoid problems? */
+	serdev_device_close(data->uart);
+
+	/* we should lookup in w2sg_by_minor */
+	minor = 0;
+	tty_unregister_device(data->tty_drv, minor);
+
+	tty_unregister_driver(data->tty_drv);
+}
+
+static int __maybe_unused w2sg_suspend(struct device *dev)
+{
+	struct w2sg_data *data = dev_get_drvdata(dev);
+
+	data->suspended = true;
+
+	cancel_delayed_work_sync(&data->work);
+
+	w2sg_set_lna_power(data);	/* shuts down if needed */
+
+	if (data->state == W2SG_PULSE) {
+		msleep(10);
+		gpio_set_value_cansleep(data->on_off_gpio, 1);
+		data->last_toggle = jiffies;
+		data->is_on = !data->is_on;
+		data->state = W2SG_NOPULSE;
+	}
+
+	if (data->state == W2SG_NOPULSE) {
+		msleep(10);
+		data->state = W2SG_IDLE;
+	}
+
+	if (data->is_on) {
+		pr_info("GPS off for suspend %d %d %d\n", data->requested,
+			data->is_on, data->lna_is_off);
+
+		gpio_set_value_cansleep(data->on_off_gpio, 0);
+		msleep(10);
+		gpio_set_value_cansleep(data->on_off_gpio, 1);
+		data->is_on = 0;
+	}
+
+	return 0;
+}
+
+static int __maybe_unused w2sg_resume(struct device *dev)
+{
+	struct w2sg_data *data = dev_get_drvdata(dev);
+
+	data->suspended = false;
+
+	pr_info("GPS resuming %d %d %d\n", data->requested,
+		data->is_on, data->lna_is_off);
+
+	schedule_delayed_work(&data->work, 0);	/* enables LNA if needed */
+
+	return 0;
+}
+
+static const struct of_device_id w2sg0004_of_match[] = {
+	{ .compatible = "wi2wi,w2sg0004" },
+	{ .compatible = "wi2wi,w2sg0084" },
+	{},
+};
+MODULE_DEVICE_TABLE(of, w2sg0004_of_match);
+
+SIMPLE_DEV_PM_OPS(w2sg_pm_ops, w2sg_suspend, w2sg_resume);
+
+static struct serdev_device_driver w2sg_driver = {
+	.probe		= w2sg_probe,
+	.remove		= w2sg_remove,
+	.driver = {
+		.name	= "w2sg0004",
+		.owner	= THIS_MODULE,
+		.pm	= &w2sg_pm_ops,
+		.of_match_table = of_match_ptr(w2sg0004_of_match)
+	},
+};
+
+module_serdev_device_driver(w2sg_driver);
+
+MODULE_AUTHOR("NeilBrown <neilb@xxxxxxx>");
+MODULE_AUTHOR("H. Nikolaus Schaller <hns@xxxxxxxxxxxxx>");
+MODULE_DESCRIPTION("w2sg0004 GPS power management driver");
+MODULE_LICENSE("GPL v2");
-- 
2.12.2