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Date:   Thu, 23 Nov 2017 10:06:11 -0600
From:   "Andrew F. Davis" <afd@...com>
To:     "H. Nikolaus Schaller" <hns@...delico.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Benoît Cousson <bcousson@...libre.com>,
        Tony Lindgren <tony@...mide.com>,
        Russell King <linux@...linux.org.uk>,
        Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Kevin Hilman <khilman@...libre.com>,
        Andreas Färber <afaerber@...e.de>,
        Thierry Reding <treding@...dia.com>,
        Jonathan Cameron <jic23@...nel.org>
CC:     <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-omap@...r.kernel.org>, <letux-kernel@...nphoenux.org>,
        <kernel@...a-handheld.com>, <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v4 3/5] misc serdev: Add w2sg0004 (gps receiver) power
 control driver

On 11/15/2017 03:37 PM, H. Nikolaus Schaller wrote:
> Add driver for Wi2Wi W2SG0004/84 GPS module connected through uart.
> 
> Use 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 NeilBrown <neilb@...e.de>
> but simplified and adapted to use the new serdev API introduced in 4.11.
> 
> Signed-off-by: H. Nikolaus Schaller <hns@...delico.com>
> ---
>  drivers/misc/Kconfig    |  10 +
>  drivers/misc/Makefile   |   1 +
>  drivers/misc/w2sg0004.c | 545 ++++++++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 556 insertions(+)
>  create mode 100644 drivers/misc/w2sg0004.c
> 
> diff --git a/drivers/misc/Kconfig b/drivers/misc/Kconfig
> index 8136dc7e863d..09d171d68408 100644
> --- a/drivers/misc/Kconfig
> +++ b/drivers/misc/Kconfig
> @@ -518,4 +518,14 @@ 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 ad0e64fdba34..abcb667e0ff0 100644
> --- a/drivers/misc/Makefile
> +++ b/drivers/misc/Makefile
> @@ -51,6 +51,7 @@ 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..12e14b5e0a99
> --- /dev/null
> +++ b/drivers/misc/w2sg0004.c
> @@ -0,0 +1,545 @@
> +// SPDX-License-Identifier: GPL-2.0

Damn this looks ugly, oh well :/

> +/*
> + * Driver for power controlling the w2sg0004/w2sg0084 GPS receiver.
> + *


Think you still need copyright tag here somewhere.

> + * 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;
> +};
> +

Kernel doc style.

> +static struct w2sg_data *w2sg_by_minor[1];
> +

If you can only have one right now then just drop the array.

> +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;
> +
> +	pr_debug("w2sg00x4 scheduled for %d\n", data->requested);
> +
> +	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 */
> +

drop extra line, same everywhere

> +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)
> +{
> +	return w2sg_by_minor[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 = {
> +};

drop the brackets? or use NULL below, not sure if this needs memory.

> +
> +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__);
> +
> +	minor = 0;
> +	if (w2sg_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;
> +
> +	w2sg_by_minor[minor] = data;
> +
> +	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;
> +	}
> +
> +	tty_port_init(&data->port);
> +	data->port.ops = &w2sg_port_ops;
> +
> +	pr_debug("w2sg call tty_port_register_device\n");
> +
> +	data->dev = tty_port_register_device(&data->port,
> +			data->tty_drv, minor, &serdev->dev);
> +
> +	pr_debug("w2sg probed\n");
> +
> +	/* 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);
> +
> +	minor = 0;
> +	tty_unregister_device(data->tty_drv, minor);
> +
> +	tty_unregister_driver(data->tty_drv);
> +}
> +
> +static int w2sg_suspend(struct device *dev)

__maybe_unused, or if PM is disabled you will get a warning.

> +{
> +	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 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_ALIAS("w2sg0004");

Is this needed?

> +
> +MODULE_AUTHOR("NeilBrown <neilb@...e.de>");

Who really wrote this?

> +MODULE_DESCRIPTION("w2sg0004 GPS power management driver");
> +MODULE_LICENSE("GPL v2");
> 

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