Date:	Fri, 17 Jul 2015 16:42:42 -0700
From:	Dmitry Torokhov <dmitry.torokhov@...il.com>
To:	Sanchayan Maity <maitysanchayan@...il.com>
Cc:	linux-input@...r.kernel.org, devicetree@...r.kernel.org,
	mark.rutland@....com, pawel.moll@....com,
	ijc+devicetree@...lion.org.uk, linux-kernel@...r.kernel.org,
	stefan@...er.ch, robh+dt@...nel.org, kernel@...gutronix.de,
	galak@...eaurora.org, shawn.guo@...aro.org,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2 3/4] touchscreen: colibri-vf50-ts: Add touchscreen
 support for Colibri VF50

Hi Sanchayan,


On Thu, Jul 16, 2015 at 08:43:21PM +0530, Sanchayan Maity wrote:
> The Colibri Vybrid VF50 module supports 4-wire touchscreens using
> FETs and ADC inputs. This driver uses the IIO consumer interface
> and relies on the vf610_adc driver based on the IIO framework.

This looks pretty good, thank you. Just a few comments below.

> 
> Signed-off-by: Sanchayan Maity <maitysanchayan@...il.com>
> ---
>  drivers/input/touchscreen/Kconfig           |  12 +
>  drivers/input/touchscreen/Makefile          |   1 +
>  drivers/input/touchscreen/colibri-vf50-ts.c | 451 ++++++++++++++++++++++++++++
>  3 files changed, 464 insertions(+)
>  create mode 100644 drivers/input/touchscreen/colibri-vf50-ts.c
> 
> diff --git a/drivers/input/touchscreen/Kconfig b/drivers/input/touchscreen/Kconfig
> index 80f6386..28948ca 100644
> --- a/drivers/input/touchscreen/Kconfig
> +++ b/drivers/input/touchscreen/Kconfig
> @@ -1027,4 +1027,16 @@ config TOUCHSCREEN_ZFORCE
>  	  To compile this driver as a module, choose M here: the
>  	  module will be called zforce_ts.
>  
> +config TOUCHSCREEN_COLIBRI_VF50
> +	tristate "Toradex Colibri on board touchscreen driver"
> +	depends on GPIOLIB && IIO && VF610_ADC
> +	help
> +	  Say Y here if you have a Colibri VF50 and plan to use
> +	  the on-board provided 4-wire touchscreen driver.
> +
> +	  If unsure, say N.
> +
> +	  To compile this driver as a module, choose M here: the
> +	  module will be called colibri_vf50_ts.
> +
>  endif
> diff --git a/drivers/input/touchscreen/Makefile b/drivers/input/touchscreen/Makefile
> index 44deea7..93746a0 100644
> --- a/drivers/input/touchscreen/Makefile
> +++ b/drivers/input/touchscreen/Makefile
> @@ -84,3 +84,4 @@ obj-$(CONFIG_TOUCHSCREEN_W90X900)	+= w90p910_ts.o
>  obj-$(CONFIG_TOUCHSCREEN_SX8654)	+= sx8654.o
>  obj-$(CONFIG_TOUCHSCREEN_TPS6507X)	+= tps6507x-ts.o
>  obj-$(CONFIG_TOUCHSCREEN_ZFORCE)	+= zforce_ts.o
> +obj-$(CONFIG_TOUCHSCREEN_COLIBRI_VF50)	+= colibri-vf50-ts.o
> diff --git a/drivers/input/touchscreen/colibri-vf50-ts.c b/drivers/input/touchscreen/colibri-vf50-ts.c
> new file mode 100644
> index 0000000..eb16bdc
> --- /dev/null
> +++ b/drivers/input/touchscreen/colibri-vf50-ts.c
> @@ -0,0 +1,451 @@
> +/* Copyright 2015 Toradex AG
> + *
> + * Toradex Colibri VF50 Touchscreen driver
> + *
> + * Originally authored by Stefan Agner for 3.0 kernel
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License as published by
> + * the Free Software Foundation; either version 2 of the License, or
> + * (at your option) any later version.
> + */
> +
> +#include <dt-bindings/gpio/gpio.h>

Why?

> +#include <linux/delay.h>
> +#include <linux/err.h>
> +#include <linux/gpio.h>
> +#include <linux/iio/consumer.h>
> +#include <linux/iio/types.h>
> +#include <linux/input.h>
> +#include <linux/interrupt.h>
> +#include <linux/kernel.h>
> +#include <linux/module.h>
> +#include <linux/of_gpio.h>

Is not used as far as I can see.

> +#include <linux/pinctrl/consumer.h>
> +#include <linux/platform_device.h>
> +#include <linux/slab.h>
> +#include <linux/types.h>
> +
> +#define DRIVER_NAME "colibri-vf50-ts"
> +#define DRV_VERSION "1.0"
> +
> +#define VF_ADC_MAX ((1 << 12) - 1)
> +
> +#define COLI_TOUCH_MIN_DELAY_US 1000
> +#define COLI_TOUCH_MAX_DELAY_US 2000
> +
> +static int min_pressure = 200;
> +
> +struct vf50_touch_device {
> +	struct platform_device	*pdev;
> +	struct input_dev	*ts_input;
> +	struct workqueue_struct *ts_workqueue;
> +	struct work_struct	ts_work;
> +	struct iio_channel	*channels;
> +	struct gpio_desc *gpio_xp;
> +	struct gpio_desc *gpio_xm;
> +	struct gpio_desc *gpio_yp;
> +	struct gpio_desc *gpio_ym;
> +	struct gpio_desc *gpio_pen_detect;
> +	struct gpio_desc *gpio_pen_detect_pullup;
> +	int pen_irq;
> +	bool stop_touchscreen;
> +};
> +
> +/*
> + * Enables given plates and measures touch parameters using ADC
> + */
> +static int adc_ts_measure(struct iio_channel *channel,
> +		  struct gpio_desc *plate_p, struct gpio_desc *plate_m)
> +{
> +	int i, value = 0, val = 0;
> +	int ret;
> +
> +	gpiod_set_value(plate_p, 1);
> +	gpiod_set_value(plate_m, 1);
> +
> +	usleep_range(COLI_TOUCH_MIN_DELAY_US, COLI_TOUCH_MAX_DELAY_US);
> +
> +	for (i = 0; i < 5; i++) {
> +		ret = iio_read_channel_raw(channel, &val);
> +		if (ret < 0)
> +			return -EINVAL;
> +
> +		value += val;
> +	}
> +
> +	value /= 5;
> +
> +	gpiod_set_value(plate_p, 0);
> +	gpiod_set_value(plate_m, 0);
> +
> +	return value;
> +}
> +
> +/*
> + * Enable touch detection using falling edge detection on XM
> + */
> +static void vf50_ts_enable_touch_detection(struct vf50_touch_device *vf50_ts)
> +{
> +	/* Enable plate YM (needs to be strong GND, high active) */
> +	gpiod_set_value(vf50_ts->gpio_ym, 1);
> +
> +	/*
> +	 * Let the platform mux to idle state in order to enable
> +	 * Pull-Up on GPIO
> +	 */
> +	pinctrl_pm_select_idle_state(&vf50_ts->pdev->dev);
> +}
> +
> +/*
> + * ADC touch screen sampling worker function
> + */
> +static void vf50_ts_work(struct work_struct *ts_work)
> +{
> +	struct vf50_touch_device *vf50_ts = container_of(ts_work,
> +				struct vf50_touch_device, ts_work);
> +	struct device *dev = &vf50_ts->pdev->dev;
> +	int val_x, val_y, val_z1, val_z2, val_p = 0;
> +	bool discard_val_on_start = true;
> +
> +	while (!vf50_ts->stop_touchscreen) {
> +		/* X-Direction */
> +		val_x = adc_ts_measure(&vf50_ts->channels[0],
> +				vf50_ts->gpio_xp, vf50_ts->gpio_xm);
> +		if (val_x < 0)
> +			continue;
> +
> +		/* Y-Direction */
> +		val_y = adc_ts_measure(&vf50_ts->channels[1],
> +				vf50_ts->gpio_yp, vf50_ts->gpio_ym);
> +		if (val_y < 0)
> +			continue;
> +
> +		/*
> +		 * Touch pressure
> +		 * Measure on XP/YM
> +		 */
> +		val_z1 = adc_ts_measure(&vf50_ts->channels[2],
> +				vf50_ts->gpio_yp, vf50_ts->gpio_xm);
> +		if (val_z1 < 0)
> +			continue;
> +		val_z2 = adc_ts_measure(&vf50_ts->channels[3],
> +				vf50_ts->gpio_yp, vf50_ts->gpio_xm);
> +		if (val_z2 < 0)
> +			continue;
> +
> +		/* Validate signal (avoid calculation using noise) */
> +		if (val_z1 > 64 && val_x > 64) {
> +			/*
> +			 * Calculate resistance between the plates
> +			 * lower resistance means higher pressure
> +			 */
> +			int r_x = (1000 * val_x) / VF_ADC_MAX;
> +
> +			val_p = (r_x * val_z2) / val_z1 - r_x;
> +
> +		} else {
> +			val_p = 2000;
> +		}
> +
> +		val_p = 2000 - val_p;
> +		dev_dbg(dev, "Measured values: x: %d, y: %d, z1: %d, z2: %d, "
> +			"p: %d\n", val_x, val_y, val_z1, val_z2, val_p);
> +
> +		/*
> +		 * If touch pressure is too low, stop measuring and reenable
> +		 * touch detection
> +		 */
> +		if (val_p < min_pressure || val_p > 2000)
> +			break;
> +
> +		/*
> +		 * The pressure may not be enough for the first x and the
> +		 * second y measurement, but, the pressure is ok when the
> +		 * driver is doing the third and fourth measurement. To
> +		 * take care of this, we drop the first measurement always.
> +		 */
> +		if (discard_val_on_start) {
> +			discard_val_on_start = false;
> +		} else {
> +			/*
> +			 * Report touch position and sleep for
> +			 * next measurement
> +			 */
> +			input_report_abs(vf50_ts->ts_input,
> +					ABS_X, VF_ADC_MAX - val_x);
> +			input_report_abs(vf50_ts->ts_input,
> +					ABS_Y, VF_ADC_MAX - val_y);
> +			input_report_abs(vf50_ts->ts_input,
> +					ABS_PRESSURE, val_p);
> +			input_report_key(vf50_ts->ts_input, BTN_TOUCH, 1);
> +			input_sync(vf50_ts->ts_input);
> +		}
> +
> +		msleep(10);
> +	}
> +
> +	/* Report no more touch, reenable touch detection */
> +	input_report_abs(vf50_ts->ts_input, ABS_PRESSURE, 0);
> +	input_report_key(vf50_ts->ts_input, BTN_TOUCH, 0);
> +	input_sync(vf50_ts->ts_input);
> +
> +	vf50_ts_enable_touch_detection(vf50_ts);
> +
> +	/* Wait for the pull-up to be stable on high */
> +	msleep(10);
> +
> +	/* Reenable IRQ to detect touch */
> +	enable_irq(vf50_ts->pen_irq);
> +
> +	dev_dbg(dev, "Reenabled touch detection interrupt\n");
> +}
> +
> +static irqreturn_t vf50_ts_touched(int irq, void *dev_id)
> +{
> +	struct vf50_touch_device *vf50_ts = (struct vf50_touch_device *)dev_id;
> +	struct device *dev = &vf50_ts->pdev->dev;
> +
> +	dev_dbg(dev, "Touch detected, start worker thread\n");
> +
> +	disable_irq_nosync(irq);
> +
> +	/* Disable the touch detection plates */
> +	gpiod_set_value(vf50_ts->gpio_ym, 0);
> +
> +	/* Let the platform mux to default state in order to mux as ADC */
> +	pinctrl_pm_select_default_state(dev);
> +
> +	queue_work(vf50_ts->ts_workqueue, &vf50_ts->ts_work);

If you convert this to a threaded interrupt you won't need to
disable/reenable interrupt or queue work. You should also be able to use
gpiod_set_value_cansleep() extending the range of ways the controller
could be connected to systems.

> +
> +	return IRQ_HANDLED;
> +}
> +
> +static int vf50_ts_open(struct input_dev *dev_input)
> +{
> +	int ret;
> +	struct vf50_touch_device *touchdev = input_get_drvdata(dev_input);
> +	struct device *dev = &touchdev->pdev->dev;
> +
> +	dev_dbg(dev, "Input device %s opened, starting touch detection\n",
> +			dev_input->name);
> +
> +	touchdev->stop_touchscreen = false;
> +
> +	ret = gpiod_direction_output(touchdev->gpio_xp, 0);
> +	if (ret) {
> +		dev_err(dev, "Could not set gpio xp as output %d\n", ret);
> +		return ret;
> +	}
> +
> +	ret = gpiod_direction_output(touchdev->gpio_xm, 0);
> +	if (ret) {
> +		dev_err(dev, "Could not set gpio xm as output %d\n", ret);
> +		return ret;
> +	}
> +
> +	ret = gpiod_direction_output(touchdev->gpio_yp, 0);
> +	if (ret) {
> +		dev_err(dev, "Could not set gpio yp as output %d\n", ret);
> +		return ret;
> +	}
> +
> +	ret = gpiod_direction_output(touchdev->gpio_ym, 0);
> +	if (ret) {
> +		dev_err(dev, "Could not set gpio ym as output %d\n", ret);
> +		return ret;
> +	}
> +
> +	ret = gpiod_direction_input(touchdev->gpio_pen_detect);
> +	if (ret) {
> +		dev_err(dev,
> +			"Could not set gpio pen detect as input %d\n", ret);
> +		return ret;
> +	}
> +
> +	ret = gpiod_direction_input(touchdev->gpio_pen_detect_pullup);
> +	if (ret) {
> +		dev_err(dev,
> +			"Could not set pen detect pullup as input %d\n", ret);
> +		return ret;
> +	}

I do not see this GPIO being actually used...

> +
> +	/* Mux detection before request IRQ, wait for pull-up to settle */
> +	vf50_ts_enable_touch_detection(touchdev);
> +	msleep(10);
> +
> +	touchdev->pen_irq = gpiod_to_irq(touchdev->gpio_pen_detect);
> +	if (touchdev->pen_irq < 0) {
> +		dev_err(dev, "Unable to get IRQ for GPIO\n");
> +		return touchdev->pen_irq;
> +	}
> +
> +	ret = request_irq(touchdev->pen_irq, vf50_ts_touched,
> +			IRQF_TRIGGER_FALLING, "touch detected", touchdev);
> +	if (ret < 0) {
> +		dev_err(dev, "Unable to request IRQ %d\n", touchdev->pen_irq);
> +		return ret;
> +	}

I'd rather we did most initialization in probe() so that -EPROBE_DEFER
would get handled properly.

> +
> +	return 0;
> +}
> +
> +static void vf50_ts_close(struct input_dev *dev_input)
> +{
> +	struct vf50_touch_device *touchdev = input_get_drvdata(dev_input);
> +	struct device *dev = &touchdev->pdev->dev;
> +
> +	free_irq(touchdev->pen_irq, touchdev);
> +
> +	touchdev->stop_touchscreen = true;
> +
> +	/* Wait until touchscreen thread finishes any possible remnants. */
> +	cancel_work_sync(&touchdev->ts_work);
> +
> +	dev_dbg(dev, "Input device %s closed, disable touch detection\n",
> +		dev_input->name);
> +}
> +
> +static inline int vf50_ts_get_gpiod(struct device *dev,
> +			struct gpio_desc **gpio_d, const char *con_id)
> +{
> +	int ret;
> +
> +	*gpio_d = devm_gpiod_get(dev, con_id);
> +	if (IS_ERR(*gpio_d)) {
> +		ret = PTR_ERR(*gpio_d);
> +		dev_err(dev, "Could not get gpio_%s %d\n", con_id, ret);
> +		return ret;
> +	}
> +
> +	return 0;
> +}
> +
> +static int vf50_ts_probe(struct platform_device *pdev)
> +{
> +	struct device *dev = &pdev->dev;
> +	struct device_node *node = dev->of_node;
> +	struct vf50_touch_device *touchdev;
> +	struct input_dev *input;
> +	int ret = 0;

Personal preference: can we call this "error"? Also no need to
gratuitously initialize it to 0.

> +
> +	if (!node) {
> +		dev_err(dev, "Device does not have associated DT data\n");
> +		return -EINVAL;

So what? I do not see you using of_node anywhere.

> +	}
> +
> +	touchdev = devm_kzalloc(dev, sizeof(*touchdev), GFP_KERNEL);
> +	if (touchdev == NULL)
> +		return -ENOMEM;
> +
> +	input = devm_input_allocate_device(dev);
> +	if (!input) {
> +		dev_err(dev, "Failed to allocate TS input device\n");
> +		ret = -ENOMEM;
> +		return ret;
> +	}
> +
> +	platform_set_drvdata(pdev, touchdev);
> +
> +	touchdev->pdev = pdev;
> +
> +	input->name = DRIVER_NAME;
> +	input->id.bustype = BUS_HOST;
> +	input->dev.parent = dev;
> +	input->open = vf50_ts_open;
> +	input->close = vf50_ts_close;
> +
> +	_set_bit(EV_ABS, input->evbit);
> +	_set_bit(EV_KEY, input->evbit);
> +	_set_bit(BTN_TOUCH, input->keybit);
> +	input_set_abs_params(input, ABS_X, 0, VF_ADC_MAX, 0, 0);
> +	input_set_abs_params(input, ABS_Y, 0, VF_ADC_MAX, 0, 0);
> +	input_set_abs_params(input, ABS_PRESSURE, 0, VF_ADC_MAX, 0, 0);
> +
> +	touchdev->ts_input = input;
> +	input_set_drvdata(input, touchdev);
> +	ret = input_register_device(input);
> +	if (ret) {
> +		dev_err(dev, "Failed to register input device\n");
> +		return ret;
> +	}
> +
> +	ret = vf50_ts_get_gpiod(dev, &touchdev->gpio_xp, "xp");
> +	if (ret)
> +		return ret;
> +
> +	ret = vf50_ts_get_gpiod(dev, &touchdev->gpio_xm, "xm");
> +	if (ret)
> +		return ret;
> +
> +	ret = vf50_ts_get_gpiod(dev, &touchdev->gpio_yp, "yp");
> +	if (ret)
> +		return ret;
> +
> +	ret = vf50_ts_get_gpiod(dev, &touchdev->gpio_ym, "ym");
> +	if (ret)
> +		return ret;
> +
> +	ret = vf50_ts_get_gpiod(dev, &touchdev->gpio_pen_detect,
> +				"pen-detect");
> +	if (ret)
> +		return ret;
> +
> +	ret = vf50_ts_get_gpiod(dev, &touchdev->gpio_pen_detect_pullup,
> +				"pen-pullup");
> +	if (ret)
> +		return ret;
> +
> +	INIT_WORK(&touchdev->ts_work, vf50_ts_work);
> +	touchdev->ts_workqueue = create_singlethread_workqueue("vf50-ts-touch");
> +
> +	if (!touchdev->ts_workqueue) {
> +		ret = PTR_ERR(touchdev->ts_workqueue);
> +		dev_err(dev,
> +			"Failed creating vf50-ts-touch workqueue %d\n", ret);
> +		return ret;
> +	}

This should go away with the threaded IRQ.

> +
> +	touchdev->channels = iio_channel_get_all(dev);
> +	if (IS_ERR(touchdev->channels))
> +		return PTR_ERR(touchdev->channels);
> +
> +	dev_info(dev, "Attached colibri-vf50-ts driver successfully\n");

Please drop, you should see message from input core about the new device
already.

> +
> +	return 0;
> +}
> +
> +static int vf50_ts_remove(struct platform_device *pdev)
> +{
> +	struct vf50_touch_device *touchdev = platform_get_drvdata(pdev);
> +
> +	destroy_workqueue(touchdev->ts_workqueue);
> +	iio_channel_release_all(touchdev->channels);
> +
> +	return 0;
> +}
> +
> +static const struct of_device_id vf50_touch_of_match[] = {
> +	{ .compatible = "toradex,vf50-touchctrl", },
> +	{ }
> +};
> +MODULE_DEVICE_TABLE(of, vf50_touch_of_match);
> +
> +static struct platform_driver __refdata vf50_touch_driver = {

Why do you need __refdata?

> +	.driver = {
> +		.name = "toradex,vf50_touchctrl",
> +		.of_match_table = vf50_touch_of_match,
> +	},
> +	.probe = vf50_ts_probe,
> +	.remove = vf50_ts_remove,
> +	.prevent_deferred_probe = false,

Deferrals are enabled by default.

> +};
> +
> +module_platform_driver(vf50_touch_driver);
> +
> +module_param(min_pressure, int, 0600);
> +MODULE_PARM_DESC(min_pressure, "Minimum pressure for touch detection");

I'd rather let userspace figure out what it recognizes as valid touch.

> +MODULE_AUTHOR("Sanchayan Maity");
> +MODULE_DESCRIPTION("Colibri VF50 Touchscreen driver");
> +MODULE_LICENSE("GPL v2");
> +MODULE_VERSION(DRV_VERSION);

Thanks.

-- 
Dmitry
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