Date:	Sat, 18 Jul 2015 18:07:33 +0530
From:	maitysanchayan@...il.com
To:	Dmitry Torokhov <dmitry.torokhov@...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

Hello Dmitry,

On 15-07-17 16:42:42, Dmitry Torokhov wrote:
> 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?

Remnant of old usage. Will fix.

> 
> > +#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.

Right. Crept in from old usage of extracting gpio information from DT. Should
have removed when I switched to using gpiod_* and removal of legacy gpio API.
Will fix.

> 
> > +#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.

I must accept I have never used threaded IRQ's. Will take a look and respin
the patch accordingly.

> 
> > +
> > +	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...

Correct. Will remove.

> 
> > +
> > +	/* 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.

Ok.

> 
> > +
> > +	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.

Ok.

> 
> > +
> > +	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.

Not required. Will fix.

> 
> > +	}
> > +
> > +	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.

Ok.

> 
> > +
> > +	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.

Ok.

> 
> > +
> > +	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?

Crept in from the old implementation. Will purge.

> 
> > +	.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.

Ok.

> 
> > +};
> > +
> > +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.

Will rethink this.

Thanks for the feedback Dmitry. Will take care of all comments in the next
version.

- Sanchayan.
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