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Date:   Mon, 23 Apr 2018 16:22:51 -0700
From:   Dmitry Torokhov <dmitry.torokhov@gmail.com>
To:     Eugen Hristev <eugen.hristev@microchip.com>
Cc:     jic23@kernel.org, ludovic.desroches@microchip.com,
        alexandre.belloni@bootlin.com,
        linux-arm-kernel@lists.infradead.org, devicetree@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-iio@vger.kernel.org,
        linux-input@vger.kernel.org, nicolas.ferre@microchip.com,
        robh@kernel.org
Subject: Re: [PATCH v3 08/11] input: touchscreen: resistive-adc-touch: add
 generic resistive ADC touchscreen
Message-ID: <20180423232251.GF66646@dtor-ws>
References: <1523350677-27106-1-git-send-email-eugen.hristev@microchip.com>
 <1523350677-27106-9-git-send-email-eugen.hristev@microchip.com>
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Hi Eugen,

On Tue, Apr 10, 2018 at 11:57:54AM +0300, Eugen Hristev wrote:
> This adds a generic resistive touchscreen (GRTS) driver, which is based
> on an IIO device (an ADC). It must be connected to the channels of an ADC
> to receive touch data. Then it will feed the data into the input subsystem
> where it registers an input device.
> It uses an IIO callback buffer to register to the IIO device
> 
> Some parts of this patch are based on initial original work by
> Mohamed Jamsheeth Hajanajubudeen and Bandaru Venkateswara Swamy
> 
> Signed-off-by: Eugen Hristev <eugen.hristev@microchip.com>
> ---
> Changes in v3:
>  - pressure now reported naturally growing down-up
>  - using helpers from touchscreen.h to parse DT properties
>  - added devm_add_action_or_reset to handle callback buffer clean on exit
>  - changed compatible and threshold property to adapt to changed bindings
> 
> Changes in v2:
>  - this is now a generic resistive adc touchscreen driver
> 
>  drivers/input/touchscreen/Kconfig               |  13 ++
>  drivers/input/touchscreen/Makefile              |   1 +
>  drivers/input/touchscreen/resistive-adc-touch.c | 200 ++++++++++++++++++++++++
>  3 files changed, 214 insertions(+)
>  create mode 100644 drivers/input/touchscreen/resistive-adc-touch.c
> 
> diff --git a/drivers/input/touchscreen/Kconfig b/drivers/input/touchscreen/Kconfig
> index 4f15496..8f85d3a 100644
> --- a/drivers/input/touchscreen/Kconfig
> +++ b/drivers/input/touchscreen/Kconfig
> @@ -92,6 +92,19 @@ config TOUCHSCREEN_AD7879_SPI
>  	  To compile this driver as a module, choose M here: the
>  	  module will be called ad7879-spi.
>  
> +config TOUCHSCREEN_ADC
> +	tristate "Generic ADC based resistive touchscreen"
> +	depends on IIO
> +	select IIO_BUFFER_CB
> +	help
> +	  Say Y here if you want to use the generic ADC
> +	  resistive touchscreen driver.
> +
> +	  If unsure, say N (but it's safe to say "Y").
> +
> +	  To compile this driver as a module, choose M here: the
> +	  module will be called resistive-adc-touch.ko.
> +
>  config TOUCHSCREEN_AR1021_I2C
>  	tristate "Microchip AR1020/1021 i2c touchscreen"
>  	depends on I2C && OF
> diff --git a/drivers/input/touchscreen/Makefile b/drivers/input/touchscreen/Makefile
> index dddae79..843c7f9 100644
> --- a/drivers/input/touchscreen/Makefile
> +++ b/drivers/input/touchscreen/Makefile
> @@ -13,6 +13,7 @@ obj-$(CONFIG_TOUCHSCREEN_AD7877)	+= ad7877.o
>  obj-$(CONFIG_TOUCHSCREEN_AD7879)	+= ad7879.o
>  obj-$(CONFIG_TOUCHSCREEN_AD7879_I2C)	+= ad7879-i2c.o
>  obj-$(CONFIG_TOUCHSCREEN_AD7879_SPI)	+= ad7879-spi.o
> +obj-$(CONFIG_TOUCHSCREEN_ADC)		+= resistive-adc-touch.o
>  obj-$(CONFIG_TOUCHSCREEN_ADS7846)	+= ads7846.o
>  obj-$(CONFIG_TOUCHSCREEN_AR1021_I2C)	+= ar1021_i2c.o
>  obj-$(CONFIG_TOUCHSCREEN_ATMEL_MXT)	+= atmel_mxt_ts.o
> diff --git a/drivers/input/touchscreen/resistive-adc-touch.c b/drivers/input/touchscreen/resistive-adc-touch.c
> new file mode 100644
> index 0000000..7e201ee
> --- /dev/null
> +++ b/drivers/input/touchscreen/resistive-adc-touch.c
> @@ -0,0 +1,200 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * ADC generic resistive touchscreen (GRTS)
> + *
> + * Copyright (C) 2017,2018 Microchip Technology,
> + * Author: Eugen Hristev <eugen.hristev@microchip.com>
> + *
> + */
> +#include <linux/input.h>
> +#include <linux/input/touchscreen.h>
> +#include <linux/iio/consumer.h>
> +#include <linux/iio/iio.h>
> +#include <linux/module.h>
> +#include <linux/of.h>
> +#include <linux/of_device.h>
> +#include <linux/platform_device.h>
> +
> +#define DRIVER_NAME					"resistive-adc-touch"
> +#define GRTS_DEFAULT_PRESSURE_THRESHOLD			50000
> +#define MAX_POS_MASK					GENMASK(11, 0)
> +
> +/**
> + * grts_state - generic resistive touch screen information struct
> + * @pressure_threshold:	number representing the threshold for the pressure
> + * @pressure:		are we getting pressure info or not
> + * @iio_chans:		list of channels acquired
> + * @iio_cb:		iio_callback buffer for the data
> + * @input:		the input device structure that we register
> + * @prop:		touchscreen properties struct
> + */
> +struct grts_state {
> +	u32				pressure_threshold;
> +	bool				pressure;
> +	struct iio_channel		*iio_chans;
> +	struct iio_cb_buffer		*iio_cb;
> +	struct input_dev		*input;
> +	struct touchscreen_properties	prop;
> +};
> +
> +static int grts_cb(const void *data, void *private)
> +{
> +	const u16 *touch_info = data;
> +	struct grts_state *st = private;
> +

Extra blank line.

> +	unsigned int x, y, press = 0xFFFF;

Why to you need to initialize "press"?

> +
> +	/* channel data coming in buffer in the order below */
> +	x = touch_info[0];
> +	y = touch_info[1];
> +	if (st->pressure)
> +		press = touch_info[2];
> +
> +	if ((!x && !y) || (st->pressure && (press < st->pressure_threshold))) {
> +		/* report end of touch */

Hm, so this makes "press" not pressure but resistance...

> +		input_report_key(st->input, BTN_TOUCH, 0);
> +		input_sync(st->input);
> +		return 0;
> +	}
> +
> +	/* report proper touch to subsystem*/
> +	touchscreen_report_pos(st->input, &st->prop, x, y, false);
> +	if (st->pressure)
> +		input_report_abs(st->input, ABS_PRESSURE, press);

and if this is resistance, then you want to have:

		input_report_abs(st->input, ABS_PRESSURE,
				 st->resistance_threshold - resistance);

> +	input_report_key(st->input, BTN_TOUCH, 1);
> +	input_sync(st->input);
> +
> +	return 0;
> +}
> +
> +static int grts_open(struct input_dev *dev)
> +{
> +	int error;
> +	struct grts_state *st = input_get_drvdata(dev);
> +
> +	error = iio_channel_start_all_cb(st->iio_cb);
> +	if (error) {
> +		dev_err(dev->dev.parent, "failed to start callback buffer.\n");
> +		return error;
> +	}
> +	return 0;
> +}
> +
> +static void grts_close(struct input_dev *dev)
> +{
> +	struct grts_state *st = input_get_drvdata(dev);
> +
> +	iio_channel_stop_all_cb(st->iio_cb);
> +}
> +
> +static void grts_disable(void *data)
> +{
> +	iio_channel_release_all_cb(data);
> +}
> +
> +static int grts_probe(struct platform_device *pdev)
> +{
> +	struct grts_state *st;
> +	struct input_dev *input;
> +	struct device *dev = &pdev->dev;
> +	struct device_node *node = dev->of_node;
> +	struct iio_channel *chan;
> +	int ret = 0;

Let's call this variable "error". There is also no need to initialize it
to 0.

> +
> +	st = devm_kzalloc(dev, sizeof(struct grts_state), GFP_KERNEL);
> +	if (!st)
> +		return -ENOMEM;
> +
> +	ret = of_property_read_u32(node, "touchscreen-threshold-pressure",
> +				   &st->pressure_threshold);

Let's use generic device property API (device_property_read_u32).


> +	if (ret < 0) {

I do not think of_ or device_ property API returns positive on success.
So simply

	if (error) {
		...
	}

> +		dev_dbg(dev, "can't get touchscreen pressure threshold property.\n");
> +		st->pressure_threshold = GRTS_DEFAULT_PRESSURE_THRESHOLD;
> +	}
> +
> +	/* get the channels from IIO device */
> +	st->iio_chans = devm_iio_channel_get_all(dev);
> +

Extra blank line.

> +	if (IS_ERR(st->iio_chans)) {
> +		if (PTR_ERR(st->iio_chans) != -EPROBE_DEFER)
> +			dev_err(dev, "can't get iio channels.\n");
> +		return PTR_ERR(st->iio_chans);
> +	}
> +
> +	chan = &st->iio_chans[0];
> +	st->pressure = false;
> +	while (chan && chan->indio_dev) {
> +		if (!strcmp(chan->channel->datasheet_name, "pressure"))
> +			st->pressure = true;
> +		chan++;
> +	}
> +
> +	input = devm_input_allocate_device(dev);
> +	if (!input) {
> +		dev_err(dev, "failed to allocate input device.\n");
> +		return -ENOMEM;
> +	}
> +
> +	input->name = DRIVER_NAME;
> +	input->id.bustype = BUS_HOST;
> +	input->open = grts_open;
> +	input->close = grts_close;
> +
> +	input_set_abs_params(input, ABS_X, 0, MAX_POS_MASK - 1, 0, 0);
> +	input_set_abs_params(input, ABS_Y, 0, MAX_POS_MASK - 1, 0, 0);
> +	if (st->pressure)
> +		input_set_abs_params(input, ABS_PRESSURE, 0, 0xffffff, 0, 0);

I am sure we can figure the range given the resistance threshold.

> +
> +	input->evbit[0] = BIT_MASK(EV_KEY) | BIT_MASK(EV_ABS);
> +	input->keybit[BIT_WORD(BTN_TOUCH)] = BIT_MASK(BTN_TOUCH);

Replace this 2 with

	input_set_capability(input, EV_KEY, BTN_TOUCH);

> +
> +	/* parse optional device tree properties */
> +	touchscreen_parse_properties(input, false, &st->prop);
> +
> +	st->input = input;
> +	input_set_drvdata(input, st);
> +
> +	ret = input_register_device(input);
> +	if (ret) {
> +		dev_err(dev, "failed to register input device.");
> +		return ret;
> +	}
> +
> +	st->iio_cb = iio_channel_get_all_cb(dev, grts_cb, st);
> +
> +	if (IS_ERR(st->iio_cb)) {
> +		dev_err(dev, "failed to allocate callback buffer.\n");
> +		ret =  PTR_ERR(st->iio_cb);
> +		return ret;
> +	}
> +
> +	ret = devm_add_action_or_reset(dev, grts_disable, st->iio_cb);

	if (error)
		return error;

> +
> +	platform_set_drvdata(pdev, st);

I do not think you are using platform device driver data anywhere.

> +
> +	return ret;

Prefer explicit success returns, so

	return 0;

> +}
> +
> +static const struct of_device_id grts_of_match[] = {
> +	{
> +		.compatible = "resistive-adc-touch",
> +	}, {
> +		/* sentinel */
> +	},
> +};
> +
> +MODULE_DEVICE_TABLE(of, grts_of_match);
> +
> +static struct platform_driver grts_driver = {
> +	.probe = grts_probe,
> +	.driver = {
> +		   .name = DRIVER_NAME,

Keep indenting with tabs please.

> +		   .of_match_table = of_match_ptr(grts_of_match),
> +	},
> +};
> +
> +module_platform_driver(grts_driver);
> +
> +MODULE_AUTHOR("Eugen Hristev <eugen.hristev@microchip.com>");
> +MODULE_DESCRIPTION("Generic ADC Resistive Touch Driver");
> +MODULE_LICENSE("GPL v2");
> -- 
> 2.7.4
> 

-- 
Dmitry